Creating+variation

**Creating Variation**

**by Liza Evans, Isabelle Levenson, and Varuna Nangia**

=MEIOSIS = __Background:__ ====Meiosis is a process which converts diploid cells to haploid gametes and which causes a change in the genetic information of those cells to create diversity in the offspring. ====

(3)
A haploid cell has only one set of chromosomes whereas a diploid cell has two sets. Most cells are diploid, while gametes are haploid. This allows them to combine and form a diploid **zygote**, which would have two sets of chromosomes, one set from each haploid gamete. (3)

(2) **Asexual reproduction** lacks the mechanism of meiosis, and there is therefore no genetic diversity created in that process. The oversimplified diagram above details the fact that all that can be created in the process of asexual replication are copies of the original cell, which lack any sort of combination of chromosomes or variation that is inherent in sexual reproduction. (3)

Phases:

(4) Break it down now! Below is Liza and Izzy's favorite song about the process. Starts at 4:42. Not that detailed, but so catchy.

media type="youtube" key="2AM-1Epzm_I" height="222" width="389" align="center" (24)

 __//Interphase//__: During interphase, which precedes meiosis I, each of the chromosomes replicates in a similar process to the replication in mitosis. The results of this phase are two genetically identical **sister chromatids** attached at their centromeres, as well as replicated centrosomes.

 __//Prophase I//__: In prophase I, the **chromosomes** begin to condense, and **homologues**, which consist of two sister chromatids, pair up. What follows is a process called **synapsis** in which a protein structure, called the **synaptonemal complex**, attaches the homologous chromosones tightly together along their lengths. In late prophase when the synaptonemal complex disappears, each chromosome pair is visible as a **tetrad** or cluster of four chromatids. The chromatids of homologous chromosomes are crisscrossed at **chiasmata**, which hold the homologous pairs together until anaphase I. At these chiasmata, segments of the chromatids are traded in a process called "**crossing over**". Also in prophase I, as in the prophase of mitosis, cellular components prepare for the division of the nucleus. The centrosomes move farther away from each other while spindle microtubules form between them. Meanwhile, the nuclear envelope and nucleoli disperse and spindle microtubules capture the kinetochores that form on the chromosomes. The chromosomes then begin to move to the metaphase plate. In comparison to the prophase of mitosis, the prophase I of meiosis I is much more complex. This phase, prophase I, lasts for days and occupies more than 90% of the time required for meiosis.

 //__Metaphase I__:// In this phase, chromosomes are arranged on the metaphase plate in homologous pairs. Attached to one chromosome of each pair are kinetochore microtubules from one pole of the cell. Microtubules from the opposite pole attach to the homologue.

 __//Anaphase I//__: The spindle apparatus guides the movement of the chromosomes to the poles. The sister chromatids remain attached at their centromeres through this process and move together towards the same pole, though the homologous chromosome moves toward the opposite pole. This differs from mitosis in that in mitosis the chromosomes are individuals on the metaphase plate rather than as pairs, and the sister chromatids separate.

 __//Telophase I and Cytokinesis//__: The members of each pair of homologous chromosomes continue to move apart until they finally reach the poles of the cell. At this point, each pole has a haploid chromosome set, but each chromosome still has two sister chromatids. Cytokinesis, the division of the cytoplasm, occurs at the same time as telophase I. Cleavage furrows in animal cells and cell plates in plant cells create the division. There is no further replication of the genetic material prior to the second division of meiosis, although in some species the chromosomes decondense and the nuclear membranes and nucleoli form again.

 __//Prophase II://__ In this phase, as in the prophase of mitosis, a spindle apparatus forms and the chromosomes progress toward the metaphase II plate.

<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;"> __//Metaphase II://__ As in mitosis and metaphase I, in metaphase II the chromosomes are positioned on the metaphase plate with the kinetochores of sister chromatids from each chromosome pointing towards opposite poles.

<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;"> __//Anaphase II://__ The centromeres of the sister chromatids finally separate in this phase. The sister chromatids of each pair, which are now individual chromosomes, move to the opposite poles of the cell.

<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">__// Telophase II and Cytokinesis //__ __//II://__ At the opposite poles of the cell, nuclei form as cytokinesis occurs. Once cytokinesis is finished, there are four daughter cells that each have a haploid number of unreplicated chromosomes. (25)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">And now, an animation to put together all the steps of meiosis into a fluid process.

media type="youtube" key="D1_-mQS_FZ0" height="315" width="420" align="center" (23)

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Prophase I: [|0:00]-[|0:43] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Metaphase I: [|0:43]-[|0:50] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Anaphase I: [|0:50]-[|1:00] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Telophase I and Cytokinesis: [|1:00]-[|1:12] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Prophase II: [|1:12]-[|1:20] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Metaphase II: [|1:20]-[|1:28] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Anaphase II: [|1:28]-[|1:33] =====

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<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 80%;">Telophase II: [|1:33]-[|1:49] =====

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">Gametes are produced by meiosis in the gonads (ovaries for females and testes in males). After meiosis occurs in the gonads, gametes are left with haploid sets of 23 chromosomes. Therefore, when a sperm (male gamete) and ova (female gamete) fuse together in fertilization, the resulting cell will have to diploid number of 46 chromosomes. The process to make sperm is called spermatogenesis while the process to make an ovum is called Oogenesis (25). = = <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 150%;">**Spermatogenesis**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">**Spermatogenesis** is the production of mature sperm cells. The basic function of spermatogenesis is to turn each diploid spermatogonium into four haploid sperm cells (25). Spermatogenesis takes place in the male reproductive organ, the testes. The testes are made up of thin, tightly composed tubules known as the **seminiferous tubules**. Sperm, which are male gametes, are produced within the walls of these tubules; as they develop and mature, the sperm make their way toward the center of the seminiferous tubules, called the **lumen** (5,7). Throughout the seminiferous tubule are **Sertoli cells**, which act like the nurse of sperm cells. Sertoli cells are extremely important in protecting germ cells, concentrating androgens near the developing germ cells, feeding the growing cells, and cleaning up/eating up the excess of the developing sperm (7).

= =



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">Spermatogenesis takes about 64 days to complete and can be divided into 5 different stages: spermatocytogenesis (mitosis), spermatidogenesis (meiosis I), spermatidogenesis (meiosis II), spermiogenesis, and spermiation (7)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">Spermatogenesis starts out with a diploid, primordial germ cell. A germ cell is any biological cell that forms gametes for sexually reproducing organisms. The primordial germ cell then differentiates to become a diploid spermatogonium. The spermatogonium enter the first stage of spermatogenesis: **spermatocytogenesis** (mitosis). In this stage **spermatogonium** are essentially stem cells that divide through **mitosis** to produce large numbers of themselves and large numbers of cells that will become mature sperm by then end of spermatogenesis. There are 3 different types of spermatogonium cells: type Ad, type Ap, and type B. **Type Ad** spermatogonium are the cells that replicate to make sure that there is a constant supply of spermatogonium. **Type Ap** are the cells that go through mitosis to produce type B spermatogonium. Type B spermatogonium are the cells that become primary spermatocytes. **Type B** spermatogonium become **primary spermatocytes** through differentiation and the onset of meiosis I (7).



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">The next stage of spermatogenesis is **spermatidogenesis (meiosis I)**. In this stage, the primary spermatocytes complete meiosis I to form two haploid cells with duplicated chromosomes called **secondary spermatocytes**. The next stage in spermatogenesis is **spermatidogenesis (meiosis II)**. In this stage, meiosis II occurs and the two haploid cells divide to form four haploid cells, each with 23 single chromosomes, called **early spermatids**. Meiosis is now complete in the spermatogenesis process (5, 7,8,25). However, at this time, the early spermatids are just a bunch of round haploid cells, sharing cytoplasm with other nuclei. The maturation and differentiation of these early spermatids into spermatozoan (sperm cells) is called **spermiogenesis**. In this stage, excess cytoplasm and materials in the cells are "eaten up" by Sertoli cells, tails begin to develop, and the DNA is repackaged. In the cytoplasmic space not taken up by the Sertoli cells, **mitochondria** (used to provide energy for the sperm cells that must swim long distances to get to the female ovum) and an **acrosome cap** (an organelle with digestive enzymes) develop. When the cell has undergone these developments, spermiogenesis is complete and the cells are now **spermatozoan (sperm cells)**. Spermatozoan are now mature enough to be released into the lumen of the seminiferous tubule (5,6).



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;"> However, although mature, the spermatozoa (sperm cells) are still not functional in the testes; in order to become fully mobile, the sperm must go through one last process: **spermiation**. In spermiation, the sperm cells move from the testes to the **epididymis**, where they acquire motility. But how do the sperm get to the epididymis if they cannot move? The sperm are moved through tubules to the epididymis by peristaltic contractions of a smooth muscle layer that lies just outside the Sertoli cells. By the time the sperm reach the epididymis, they are fully developed and completely mobile (6).



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">Here is a very clear and concise animation on Spermatogenesis. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">[] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 14px; line-height: 21px;">(21).

<span style="background-color: #ffffff; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 150%;">**Oogenesis**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">** Oogenesis ** is the production of mature **ova**, which are unfertilized egg cells. Oogenesis takes place in the female reproductive organ, the ovary. Oogenesis can be divided into 2 main stages: oocytogenesis and ootidogenesis (9). <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;"> Oogenesis starts with a primordial germ cell which differentiates into Oogonium. **Oogonium** are stem cells that proliferate through **mitosis** so that by the seventh month of gestation, about 7 million oogonium have formed. Most oogonium die, however, so that the remaining number decreases to 1-2 million by birth. The **oocytogenesis** stage of oogenesis is when oogonium differentiate to form **primary oocytes**. Like the oogonium, the primary oocyte is a diploid cell, containing two complete sets of chromosomes (9,10). The next stage of Oogenesis is **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">Ootidogenesis **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">. Ootidogenesis, is the process in which a primary oocyte develops into an ovum, the haploid result. Ootidogenesis encompasses both **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">meiosis I, and meiosis II **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">. Primary oocytes go through meiosis I, but become arrested in the prophase stage ( **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">diplotene stage **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">) in small follicles until puberty. The cells are reactivated to grow and induce the primary oocyte when stimulated by the hormone **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">FSH **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;"> (follicle-stimulating hormone)(9, 25). When this happens, the primary oocyte completes meiosis I, forming two haploid cells, through unequal **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">cytokinesis **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">. Because of unequal cytokinesis, one of the two cells contains hardly any cytoplasm, whereas the other cell has nearly the entire volume of cellular components. The smaller cell is called the **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">first polar body **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">, and the larger cell is referred to as the **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">secondary oocyte **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">. While the polar body may or may not divide again, the secondary oocyte does complete meiosis II. However, at the metaphase stage, the cell arrests until a sperm enters it. The entry of a sperm results in the completion of meiosis II where unequal cytokinesis occurs once again forming two or four (if the first polar body divides) haploid cells. The results of meiosis II on the secondary oocyte result in a **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">second polar body **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;"> and an **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">ovum **<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">, a female gamete. Unlike spermatogenesis where four haploid sperm cells are created, in Oogenesis, only one mature ovum develops, while the other three polar bodies disintegrate (9,10,25).



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 110%;">However, in order to fully understand oogenesis, it is also important to understand the ovarian cycle. The ovarian cycle can be split up into 3 distinct phases: the follicular phase, ovulation, and the luteal phase. The **follicular stage,** which begins due to the release of the hormone **FSH,** begins during ootidogenesis(meiosis I )when oogonium turn into primary oocytes. However, the primary oocytes become restructured so that each one enveloped by a single layer of follicular epithelial cells called an **ovarian follicle**. During the follicular phase, the developing egg in each of these follicles enlarges and the coat thickens. However, from all the follicles that started out developing, only one ovarian follicle continues to grow and develop while the rest break down. The ovarian follicle that continues to mature develops an internal fluid-filled cavity and gets very big. The **ovulation** phase begins when the follicle and adjacent wall rupture, releasing the secondary oocyte into the fallopian tubes where it is available to be fertilized. The follicular tissue that remains in the ovary after ovulation turns into the **corpus luteum**. During the luteum stage, endocrine cells in the corpus luteum secrete female hormones that help a new ovarian cycle to begin(25).



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Although this a short video, it combines Oogenesis and the ovarian cycle pretty well. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">[](22)

=<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">FERTILIZATION = <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">information from our textbook, source 25

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**Fertilization**, or **syngamy**, is the union of gametes. The main purposes of fertilization are to combine the haploid sets of chromosomes of a father and mother to create a single diploid cell and to activate the egg. Fertilization occurs when the haploid gamete of the father or sperm cell reaches and fuses with the haploid gamete of the mother or ovum. The result of this union is a fertilized egg, called a **zygote. (25)**

__<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Fertilization in sea urchins (similar to vertebrate fertilization): __

(26)

> t eggs will be fertilized by only sperm from the same species.
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">//Contact:// The gametes are released into the water, and a sperm cell is exposed to the molecules from the dissolving jelly coat surrounding the sea urchin egg.
 * 2) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">//Acrosomal reaction:// A vesicle at the tip of the sperm called the acrosome discharges its contents via exocytosis. The resulting **acrosomal reaction** releases hydrolytic enzymes which enable a structure called the **acrosomal process** to penetrate the jelly coat.
 * 3) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">//Growth of acrosomal process:// The tip of this acrosomal process is coated with a protein which adheres to receptor molecules that are located on the vitelline layer under the jelly coat. A recognition mechanism ensures tha
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">//Fusion of the plasma membranes//: The fusion of the sperm and egg plasma membranes follows the acrosomal reaction. This fusion causes ion channels to open in the egg's plasma membrane, therefore allowing sodium ions to flow into the egg cell and change the membrane potential, which signals a membrane depolarization. Since this membrane depolarization prevents more than one sperm cell from fusing with the egg, it is often called the **fast block to polyspermy**.
 * 2) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">//Cortical reaction:// The **cortical reaction** is a series of changes in the cortex of the egg cytoplasm. The fusion of the sperm and the egg triggers a signal-transduction pathway that causes the endoplasmic reticulum of the egg to release calcium into the cytosol, resulting in the production of the "second messengers" like DAG and IG3, which opens ligand-gated calcium channels in the ER membrane. With more Ca^2+ released, the opening of other channels is triggered. The high concentration of calcium causes a change in the vesicles that lie just under the egg's plasma membrane, which are called **cortical granules**. The cortical granules fuse with the plasma membrane and release their contents into the perivitelline space between the plasma membrance and the vitelline layer. At this point, enzymes from the granules separate the vitelline layer from the plasma membrane and mucopolysaccharides produce an osmotic gradient which pulls water into the perivitelline space and causes it to swell. This swelling pushes the vitelline layer away from the plasma membrane. Other enzymes harden it. The vitelline layer then therefore becomes the **fertilization envelope**, which blocks the entry of additional sperm. A this time, the voltage across the plasma membrane has returned to normal, so the fast block to polyspermy no longer functions, but the fertilization envelope functions as a **slow block to polyspermy**. (25)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">This video shows the process of fertilization in a sea urchin:

media type="youtube" key="jp-RgIRgcYE" height="315" width="420" align="center" (28)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">__Activation of the egg:__ <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The rise in the Ca^2+ concentration of in the egg's cytosol also incites metabolic changes with the egg cell, which unfertilized has a very slow metabolism. After fertilization, the rates of cellular respiration and protein synthesis increase within minutes, so therefore the cell is said to have been "activated". In sea urchins and some other species, the DAG that was produced during the cortical reaction activates a membrane protein which transports H+ out of the egg. This makes the egg slightly alkaline; this change in pH is said to indirectly responsible for the metabolic responses of the egg to fertilization. Sperm cells do not contribute any materials required for activation. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">While the egg increases its metabolic activity, the sperm cell's nucleus that is within the egg starts to swell. It then merges with the egg nucleus to create the diploid nucleus of the zygote. Now, DNA synthesis begins and cell divisions start. (25)

__<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Fertilization in mammals: __

(27) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Many of the events are similar to those in sea urchins, although there are important differences.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Fertilization in terrestrial mammals is generally internal
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**Capacitation**: secretions in the female mammal reproductive tract alter molecules on the sperm cell surface and enhance sperm function
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The mammalian egg is cloaked by follicle cells released with the egg during ovulation. A capacitated sperm cell must go through this layer of follice cells before reaching the **zona pellucida** or extracellular matrix of the egg, which consists of three different glycoproteins that form filaments in a 3D network.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">One of the glycoproteins in the zona pellucida, ZP3, functions as a sperm receptor, and the binding of the sperm head to such receptors induces the acrosome to release its contents
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Acrosomal reaction enables the sperm to penetrate the zona pellucida and reach the plasma membrane of the egg and exposes a protein in the sperm membrane that fuses with the egg membrane
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The binding of the sperm and egg triggers the depolarization key to the fast block to polyspermy. A cortical reaction then occurs. Enzymes from the cortical granules catalyze changes in the zona pellucida, and these changes act as the slow block to polyspermy.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Extensions of the egg cell, microvilli, take the sperm cell into the egg. The basal body of the sperm's flagellum divides to form two centrosomes with centrioles in the zygote because unfertilized mammalian eggs do not have their own centrosomes.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The haploid nuclei of the sperm and egg do not fuse immediately. The sperm's and egg's nuclear envelopes disperse and the chromosomes from the two gametes share a common spindle apparatus. After the first mitotic division, as diploid nuclei form in the two daughter cells, the chromosomes from the parents finally join together in common nuclei to become the genome of the offspring. (25)

=<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">GENOMIC IMPRINTING =

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Epigenetics
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">In [|biology], and specifically [|genetics] , epigenetics is the study of heritable changes in [|gene expression] or cellular phenotype caused by mechanisms other than changes in the underlying [|DNA] sequence It refers to functionally relevant modifications to the genome that do not involve a change in the nucleotide sequence. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Examples of such changes are [|DNA methylation] and [|histone modification], both of which serve to regulate gene expression without altering the underlying DNA sequence.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Methylation
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Methyl groups (-CH3) attach to DNA bases after DNA is synthesized. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">In flowering plants and animals, cytosine is usually the methylated base. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Inactive DNA is usually highly methylated, leading to hypothesis that methylation turns off genes and demethylization can turn them back on. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Ex. Mammalian x chromosomes, tissues <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Some genes, de-methylating turns on <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">In both plants and animals, methyalation enzyme deficiency leads to abnormalities in embryonic development <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">During mitosis, methylation enzymes act on DNA sites of daughter strand after every round of DNA replication, therefore, patterns are passed on. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Tissue cells’ methylation patterns act as chemical record for what occurred during embryonic development.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Genomic Imprinting
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">[|An Animation on Genetic Imprinting] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">In Genomic Imprinting, the allele has a different effect depending on whether it was inherited from mother or father, but this is not sex linked inheritance, but something different. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">The gene on one chromosome is expressed while its allele on a homologous chromosome is turned off during spermatogenesis and oogenesis. This is one type of epigenetic silencing. In mammals, genes can have different effects depending on if they’re from the mother or father. Next generation, maternal and paternal imprints are “erased” and gamete re-imprinting occurs after fertilization with a certain gender in mind. After that, the genetic tags rarely change during the organism’s life and the epigenetic tags influence development. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Basically a genomic imprint is the pattern of methyl groups added to cystosine nucleotides of alleles. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Hypothesis: Methyalation silences gene, use non methylated allele <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Twenty genes on 9 chromosomes have yet been discovered in which genetic imprinting plays a role. There might be hundreds more to be discovered <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">With imprinted genes, we only receive one functional copy, either from the mother or the father. Genetic Imprinting is unique to flowering plants and mammals.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Case Study One: Prader Willi Syndrome and Angelman Syndrome
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Prader-Willi and Angelman syndrome are both caused by issues with the same area on chromosome 15. Those with Angelman Syndrome have learning problems, speech difficulties, seizures, jerky movement, and an unusually happy disposition. This is caused by missing a gene that is normally inherited from the mother or having two paternal copies. Prader-Willi Syndrome sufferers have learning problems, short stature, and eat compulsively. Those with this disease are missing a gene normally from the mother or have two paternal copies.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Case Study Two: The Igf2 Gene
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">The Igf2 gene codes for a hormone that causes fetal and embryonic growth. Usually, methyl tags silence the maternal Igf2 gene. When an epimutation leaved the maternal gene un-methylated, there are two copies of the gene so overgrowth occurs. This is called Beckwith-Wiederman Syndrome.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Genetic Imprinting and Cloning
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Epigenetic tags such as those involved in genetic imprinting have been one of the greatest obstacles to cloning. In cloning, the differentiated cell already has the epigenetic tags in place and the process for erasing epigenetic tags has a high error rate, so the methyalation process gets messed up.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Case Study Three: Ligers and Tigons
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Imprinted genes are under greater selective pressure, since only one copy is expressed at a time, so all variations will be expressed. Imprinting patterns evolve so rapidly that the imprinting patterns in closely related organisms are often drastically different. In Tigers, the gene for growth is imprinted on the female, whereas in lions, it is imprinted on the male. Therefore, in hybridization, a male tiger and a female lion produce a liger, which is the biggest of the big cats. However, a female tiger and a male lion produce a tion, which is smaller than either of its parents.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Many of such genes involve development of embryo as well as growth and metabolism.
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> But Why? It all has to do with promiscuous cats, Darwin and the genetic conflict hypothesis. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">You see, in cats and many other animals, more than one male can father offspring in one litter. For male cats, it is in their interest for their offspring to grow larger and outlive their twin siblings from a different father. That is why maternal growth genes are often imprinted while paternal genes are expressed. For mothers, it is in their interest for all the offspring to survive, on Darwin’s standards. She needs to divide her resources (warmth, nutrients, energy) among her kittens. Therefore, it makes sense that metabolic genes are often imprinted paternally and expressed maternally.



<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">**Sources:**

<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">**Meiosis info:** <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">1. http://lmg.letmeget.net/blog/haploid-and-diploid-cells-humans <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">Picture of Haploid and Diploid Chromosome <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">2. http://www.botany.hawaii.edu/faculty/wong/Bot201/Ascomycota/Fission.jpg

<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">Simplified Diagram of Asexual Reproductio <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">3. http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3.html <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Meiosis tutorial that was very straignt-forward and simple. Great for basic information. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">4. http://www.phschool.com/science/biology_place/labbench/lab3/concepts2.html <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">Very clear diagram for Meiosis I and II. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">5. [] <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">Probably the best website at explaining spermatogenesis in a clear and concise way. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">6. []Clears up any confusion and superfluous info other websites give on the maturation of a cell; very clear and easy to understand. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">7. []Extremely detailed. While used much during this project, it can be very confusing and overwhelming. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">8. []A very simplified version of spermatogenesis that helps if one just wants to know the basics. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">9. []This site gives extremely detailed info on Oogenesis. Can be overwhelming and confusing to a reader.. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">10. []Good website for getting basics of Oogenesis in a clear way. Extremely helpful!

<span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">//**Genetic Imprinting Info**// <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">11. [|A Great Source on Genetic Imprinting by University of Utah] <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">12. [|a simple definition of epigenetics to help gain understanding that might help understanding the context in this page] <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">13. []This is a picture of a mature, motile sperm. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">14. []This picture is clear at showing how the spermatagonium are stem cells. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">15. []This is a picture that gives a really clear and detailed overview of Spermatogenesis. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">16. []This is a picture that shows that spermatogenesis takes place in the seminiferous tubule. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">17. []This picture shows the maturation of sperm in all of its stages. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">18. []This s a picture of a mature ovum. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">19. []This is a picture that gives a basic overview of Oogenesis. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">20. []This is a picture that gives a detailed overview and shows the connection between Oogenesis and the ovarian cycle. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">21. []This animation gives an excellent overview of the basics of Spermatogenesis. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">22. []This youtube video, while bad at explaining Oogenesis, is great at showing interaction between Oogenesis and the ovarian cycle. <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">23. Meiosis animation, very detailed: http://www.youtube.com/watch?v=D1_-mQS_FZ0 <span style="display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">24. Our favorite meiosis song!: http://www.youtube.com/watch?v=2AM-1Epzm_I&feature=related <span style="background-color: white; display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">25. Biology by Cambell the sixth and eighth editionsOur bio textbook. <span style="background-color: white; display: block; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%; text-align: left;">26. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">@http://bio1152.nicerweb.com/Locked/media/ch47/acrosomal.html <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Photo for fertilization in sea urchins <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">27. http://en.wikipedia.org/wiki/Fertilisation <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Photo for fertilization in humans <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">28. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">http://www.youtube.com/watch?v=jp-RgIRgcYE <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Sea urchin fertilization breakdown video

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">**__Multiple Choice__**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">1.An imprinted gene

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> a. is methylated and therefore will be expressed <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> b. is methylated and therefore will not be expressed <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> c. is not methylated and therefore will be expressed <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> d. is not methylated and therefore won’t be expressed <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> e. gets passed on by one parent and selects gender

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">2. Epigenetics

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">a. were discovered by Darwin and involve selective pressures <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">b. Were discovered by Mendel and involve heritability <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. Were discovered by Lamarch and prove the heritability of changes over a lifetime <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. Are heritable changes in gene expression not caused by DNA <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. Are considered a type of pseudo-science

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">3. How does selective pressure work on imprinted genes?

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. selective pressures do not work on imprinted genes <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. selective pressure work on imprinted genes less than other genes <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. selective pressures work equally on imprinted and non imprinted genes <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. selective pressure work slightly more on imprinted genes than non imprinted genes <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. selective pressure work much more rapidly on imprinted genes than non imprinted

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">4. During spermiogenesis, which cells are the first to become haploid?

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. spermatids <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. spermatogonium <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. primary spermatocytes <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. secondary spermatocytes <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. sperm cells

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">5. The best answer for where spermatogenesis takes place is?

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. testis <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. seminiferous tubules <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. epididymis <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. urethra <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. prostate gland

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">6. A difference between spermatogenesis and oogenesis is ?

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. the mature ovum is diploid while the sperm is haploid <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. the mature ovum is haploid while the sperm is diploid <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. spermatogenesis involves both mitosis and meiosis while oogenesis only involves meiosis <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. only one mature ovum is produced in oogenesis while 4 mature sperm are produced in spermatogenesis <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. the production of ovum stops at puberty while the production of sperm is continuous

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">7. What is the purpose of polar bodies in oogenesis?

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. they are a result of unequal cytokinesis and serve no function <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. they can produce mature ovum <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. they produce sets of multiple births <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. they ensure the ovum will have most of the cytoplasm <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;"> e. they rid the body of defective chromosomes, leaving the good set within the ovum.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">8. Which of the following actions occur during prophase I of meiosis?

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">I. Chromosomes condense <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">II. Synapsis <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">III. Crossing over at the chiasmata <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">IV. Chromosomes begin moving towards the metaphase plate

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. I only <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. I and II <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. III only <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. I, III, and IV <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. I, II, III, and IV

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">9. Which of the following regarding the differences between meiosis I and meiosis II is FALSE?

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. Meiosis I is preceded by interphase, while meiosis II is not <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. Sister chromatids remain attached in meiosis I but separate in meiosis II <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. Crossing over occurs only in meiosis II, not in meiosis I <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. Chiasmata and tetrads exist only in meiosis I <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. All answers are true

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">10. Which of the following is an accurate summary of the fast block to polyspermy?

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. The cortical reaction causes swelling of the perivitelline space and results in the vitelline layer pushing away from the plasma membrane and hardening to become the fertilization envelope <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. The cortical reaction causes the vitelline layer to disintegrate and the plasma membrane to replace it as a more selective fertilization envelope <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. The fusion of the egg and sperm plasma membranes causes an influx of sodium ions, which signals a membrane depolarization <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. The fusion of the egg and sperm plasma membranes causes an influx of calcium ions, which work to stiffen the fertilization envelope <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. Hydrolytic enzymes released during the acrosomal reaction destroy any sperm cells that attempt to fuse with the egg

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">11. Which of the following is not a key difference between vertebrate and mammalian fertilization?

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">a. Capacitation <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">b. The zona pellucida <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">c. The absorption of the sperm <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">d. The slow fusion of the haploid nuclei <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">e. The cortical reaction

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> __**Essay**__

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">Write an essay about meiosis, making sure to cover the following topics:


 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">the stages of meiosis
 * 2) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">the differences between oogenesis and spermatogenesis
 * 3) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 90%;">how meiosis leads to variation