Ch 2 - Reproduction

Question 1

Prototherians(monotremes):

Answer 1

Include platypus and echidna incase embryos within eggs – referred to as oviparity

Question 2

Metatherians (marsupials):

Answer 2

include koalas and kangaroos. Fetus undergoes development in the uterus and then climbs out of the birth canal into the marsupium or pouch.

Question 3

In animals, autosomal cells are __, while germ cells are __

Answer 3

diploid(2n), haploid(n)

Question 4

4 stages of cell cycle

Answer 4

G1, S, G2, M. The first 3 are known as interphase, the longest part of the cycle. Cells that do no divide spend all their time in G0 phase. In G0, cells simply live without preparing for division.
During interphase, chromosomes are in a less condensed form known as chromatin. This is because the DNA must be available for RNA polymerase to transcribe the genes. During mitosis it is preferable to condense the DNA into tightly coiled chromosomes to avoid losing genetic material during cell division

Question 5

During G1:

Answer 5

cells create organelles for energy and protein production while also increasing in size. Passage into S phase is governed by a restriction point which checks for criteria such as proper complement of DNA.

Question 6

During S:

Answer 6

cell replicates its genetic material so each daughter will have identical copies. Each chromosome now consists of 2 identical chromatids known as sister chromatids that are bound together at the centromere. Ploidy doesn’t change. Humans still have 46 chromosomes, but 92 chromatids compared to 46 chromatids before. Cells entering G2 have 2x the DNA as cells in G1. Chromatid is composed of complete DNA molecule. Chromosome may be used to refer to a single chromatid before S phases, or a pair of chromatids after S phase

Question 7

During G2:

Answer 7

cell passes through another checkpoint. Checks there are enough organelles and cytoplasm for the 2 daughter cells and that DNA replication proceeded correctly.

Question 8

During M:

Answer 8

mitosis and cytokinesis.
Mitosis consists of: prophase, metaphase, anaphase, telophase.
Cytokinesis is the splitting of cytoplasm and organelles between daughter cells. In autosomal cells, division results in genetically identical daughter cells.

Question 9

Cell cycle checkpoints and cyclins

Answer 9

G1/S checkpoint determines if the DNA is good enough for synthesis, mainly controlled by p53.
G2/M checkpoint mainly focuses on if the cell has reached adequate size and organelles have been properly replicated. P53 plays a role.
Molecules responsible for the cell cycle are cyclins and cyclin dependent kinases (CDK). Cyclins binds to CDKs creating an active CDK-cyclin complex. Complex can then phosphorylate transcription factors. Transcription factors promote transcription of genes required for the next stage.

Question 10

Cell cycle of cancer

Answer 10

When cell cycle becomes deranged and damaged cells undergo mitosis, cancer may result. One of the most common mutations in cancer is TP53. If this gene is mutated, cell cycle does not stop to repair damaged DNA. Mutations accumulate, resulting in cancerous cells that divide continuously. Often, cancer cells undergo rapid division to create tumors. Eventually the damaged cells can reach other tissues by local invasion or through the bloodstream/lymphatic system. Latter results in metastasis.

Question 11

Prophase: - chromosomes condense, spindle forms.

Answer 11

1. Chromatins condense into chromosomes. Centriole pairs move towards opposite ends of the cell. Centrioles are located outside the nucleus at the centrosome and are responsible for correct division of DNA.
2. Centrioles form spindle fibers which are made of microtubules. This establishes the centrosome as one of the two microtubule organizing centers. Some microtubules form asters that anchor centriole to the plasma membrane.
3. Nuclear membrane dissolves, spindle fibers contact chromosomes at the centromere. Kinetochores appear at the centrosome and serve as attachment points for specific fibers of the spindle apparatus known as kinetochore fibers.

Question 12

Metaphase – Chromosomes align

Answer 12

1. Kinetochore fibers interact with the fibers of the spindle apparatus to align the chromosomes at the metaphase plate (equatorial plate).

Question 13

Anaphase – Sister chromatids separate

Answer 13

1. Centromeres split so each sister chromatid has its own centromere. Sister chromatids are pulled towards opposite poles by shortening of the kinetochore fibers

Question 14

Telophase – New nuclear membranes form

Answer 14

1. Reverse of prophase. Spindle apparatus disappears. Nuclear membrane reforms around set of new chromosomes. Chromosomes uncoil

Question 15

Cytokinesis:

Answer 15

Separation of the cytoplasm and organelles. Each cell undergoes a finite amount of divisions before programmed death. In human somatic cells – between 20 & 50.

Question 16

Meiosis occurs in

Answer 16

germ cells or gametophytes, results in 4 nonidentical sex cells or gametes.

Question 17

Meiosis and Mitosis compare and contrast.

Answer 17

Similarities: genetic material is duplicated, chromatin condenses to form chromosomes, microtubules emanating from the centrioles involved in diving genetic material
Differences: Meiosis has 1 round of replication followed by 2 rounds of division.

Question 18

Meiosis I and II

Answer 18

Meiosis I results in homologous chromosomes being separated resulting in haploid daughter cells, known as reductional division.
Meiosis II results in separation of sister chromatids without a change in ploidy, known as equational division.

Question 19

Human genome composed of 23 pairs of homologous chromosomes. Each contain 1 chromosome inherited from each parent. Homologous pairs are considered separate chromosomes; sister chromatids are identical strands of DNA connected at the centromere. After S phase, 92 chromatids organized into 46 chromosomes organized into 23 pairs.

Question 20

Prophase I:

Answer 20

Chromatin condenses into chromosomes, spindle apparatus forms, nuclear member disappears. Homologous chromosomes come together and intertwine in a process called synapsis. Each synaptic pair contains 4 chromatids known as a tetrad. Homologous chromosomes are held together by a group of proteins called the synaptonemal complex. Chromatids of homologous chromosomes may break at the point of contact, called the chiasma, and exchange equivalent pieces of DNA. This process is called crossing over and can include single or double crossovers. Such genetic recombination can unlink linked genes, increasing the variety of combinations produced via gametogenesis. Linkage is the tendency for genes to be inherited together; genes located father from each other physically are less likely to be inherited together, and more likely to undergo crossing over. Each daughter cell has a unique pool of alleles from maternal and paternal origin, which explain independent assortment (inheritance of one allele has no effect on the likelihood of inheritance of another allele; Mendels 2nd law.)

Question 21

Metaphase I

Answer 21

Tetrads align at the metaphase plate and each pair attaches to a separate spindle fiber by its kinetochore. Held together by only 1 spindle fiber (mitosis is 2)

Question 22

Anaphase I

Answer 22

Homologous pairs separate and are pulled to opposite poles of the cell, known as disjunction. Chromosome of paternal and maternal origin splits, and either chromosome can end up in either daughter cell. The distribution is random, and accounts for Mendels 1st law. Separation of 2 homologous chromosomes referred to as segregation.

Question 23

Telophase I

Answer 23

Nuclear membrane forms around each new nucleus. Each chromosome still consists of 2 sister chromatids joined at the centromere. Cells are haploid. Cell divides into 2 daughter cells by cytokinesis. Between cell divisions, there may be a short rest period or interkinesis.

Question 24

Meiosis II

Answer 24

Sister chromatids are separated.

Question 25

Prophase II

Answer 25

Nuclear envelope dissolves, centrioles migrate to opposite ends, spindle apparatus forms

Question 26

Metaphase II

Answer 26

Chromosomes line up at metaphase plate

Question 27

Anaphase II

Answer 27

Centromeres divide, separating chromosome into sister chromatids, which are pulled to opposite ends by spindle fibers

Question 28

Telophase II

Answer 28

Nuclear membrane forms around each new nucleus. Cytokinesis follows, and 2 daughter cells are formed. Up to 4 total haploid daughter cells per gametocyte.

Question 29

X linked disorder

Answer 29

X chromosome carries a sizeable amount of genetic information; mutations in these genes can cause sex-linked disorders. Males are termed hemizygous with respect to many of the genes on the X chromosome because they only have one copy. Therefore, a male with a disease-causing allele on the unpaired X chromosome will necessarily express that allele. Females may be homozygous or heterozygous for genes on the X chromosome. Most X-linked disorders are recessively inherited; therefore, females express sex-linked disorders less frequently than males. Females carrying diseased alleles on the X chromosome but not exhibiting the disease are known as carriers.

Question 30

Y chromosome contains very little genetic information. One notable gene is the SRY or sex-determining region Y, which codes for transcription factors that initiates testis differentiation and the formation of male gonads

Answer 30

Ova carries only X chromosome, while sperm carry X or Y.

Question 31

Male reproductive organs

Answer 31

Primitive gonads develop into testes. Gonads are reproductive organs. Testes have two functional components: seminiferous tubules and interstitial cells of Leydig. Sperm are produced in the highly coiled seminiferous tubules, where they are nourished by the Sertoli cells. The cells of Leydig secrete testosterone and other male sex hormones (androgens). Testes are located in the scrotum, an external pouch that hangs below the penis. Layer of muscle around the vas deferens to maintain proper temperature for sperm development.

Question 32

Sperm passage

Answer 32

As sperm are formed, they are passed to the epididymis where the flagella gain motility and are stored until ejaculation. During ejaculation sperm travel through the vas deferens and enter the ejaculatory duct at the posterior edge of the prostate gland. The two ejaculatory ducts then fuse into the urethra, which carries sperm through the penis as they exit the body. In males, reproductive and urinary systems share a common pathway.
SEVE(N) UP

Question 33

Seminal fluid

Answer 33

As sperm pass through the reproductive tract, they are mixed with seminal fluid which is produced through a combined effort by the seminal vesicles, prostate gland, and bulbourethral gland. Seminal vesicles contribute fructose to nourish sperm, and both seminal vesicles and prostate gland give the fluid mildly alkaline properties so sperm can survive the acidity of female reproductive tract. The bulbourethral (Cowper’s) glands produce a clear viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal. The combination of sperm and seminal fluid is known as semen.

Question 34

Spermatogenesis

Answer 34

The formation of haploid sperm through meiosis, occurs in seminiferous tubules. In males diploid stem cells are spermatogonia. After replicating their genetic material (S phase) they develop into primary spermatocytes. The first meiotic division results in secondary spermatophytes, which then undergo Meiosis II to generate haploid spermatids. Finally, spermatids undergo maturation to become mature spermatozoa. Spermatogenesis results in 4 functional sperm for each spermatogonium.

Question 35

Mature sperm

Answer 35

Mature sperm contain a head(containing genetic material), a midpiece(which generates ATP from fructose), and a flagellum ( for motility). Midpiece is filled with mitochondria which generate energy for swimming through the female reproductive tract to reach the ovum in the fallopian tubes. Sperm head is covered by a cap known as an acrosome. This structure is derived from the Golgi apparatus and is necessary to penetrate the ovum

Question 36

Female reproductive organs

Answer 36

Primarily internal. Gonads known as ovaries produce estrogen and progesterone. Ovaries located in the pelvic cavity; each consist of thousands of follicles which are multilayered sacs that contain, nourish, and protect immature ova (eggs). Between puberty and menopause, one egg per month is ovulated into the peritoneal sac, which lines the abdominal cavity. Egg is then drawn into the fallopian tube or oviduct, which is lined with cilia to propel the egg forward. Fallopian tubes connected to the muscular uterus, the site of fetal development. Lower end of the uterus known as the cervix, which connects to the vaginal canal, where sperm are deposited. External parts of the female genital organs known collectively as vulva. Females have separate excretory and reproductive tracts.

Question 37

Oogenesis

Answer 37

Gametocytes undergo the same meiotic process in both females and males, but there are some differences. First, there is no unending supply of stem cells; all the oogonia a female will ever have are formed during fetal development. By birth, all oogonia have already undergone DNA replication and are considered primary oocytes. These cells are diploid and are remained paused in Prophase I. After menarche (1st menstrual cycle), one primary oocyte per month will complete meiosis I, producing a secondary oocyte and a polar body. At ovulation, the egg cell has completed meiosis I and is arrested in meiosis II as a secondary oocyte. Secondary oocyte remains paused in Metaphase II until fertilization occurs.

Question 38

Zone pellucida and the corona radiata.

Answer 38

2 layers that surround the oocyte. The zone pellucida surrounds the oocyte itself and is an acellular mixture of glyco-proteins that protects the oocyte and contains compounds necessary for sperm cell binding. Corona radiata lies outside the zona pellucida and is a layer of cells that adheres to the oocyte during ovulation. Meiosis II is triggered when a sperm cell penetrates these layers. Secondary oocyte then splits into a mature ovum and another polar body.

Question 39

Mature ovum

Answer 39

Mature ovum is very large and contribute nearly everything to the zygote - the cytoplasm, organelles, and RNA for early cellular process. Upon completion of Meiosis II, haploid pronuclei of the sperm and the ovum joint, creating a diploid zygote

Question 40

sexual development

Answer 40

Ability to reproduce is under hormonal control. Prior to puberty, the hypothalamus restricts production of gonadotropin-releasing hormone (GnRH). At the start of puberty, this restriction is lifted as the hypothalamus releases pulses of GnRH, which triggers the anterior pituitary gland to synthesize and release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones trigger the production of other sex hormones that develop and maintain the reproductive system.

Question 41

Male sexual development

Answer 41

During the fetal period, presence of the Y chromosome leads to production of androgens, resulting in male sexual differentiation. Testosterone, produced by the testes, increase dramatically during puberty and sperm production begins. FSH stimulates the Sertoli cells and triggers sperm maturation. LH causes the interstitial cells to produce testosterone, which develops and maintains the male reproductive system while resulting in the development of secondary sexual characteristics including facial and auxiliary hair, deepening of the voice, and increased muscle and bone mass. Testosterone exerts negative feedback on the hypothalamus and anterior pituitary gland, so production is kept in appropriate range.

Question 42

Female sexual development

Answer 42

The ovaries which are derived from the same embryonic structures as the testes, are also under the control of FSH and LH secreted by the anterior pituitary. Ovaries produce estrogen and progesterone.
Estrogens are secreted in response to the FSH and result in development and maintenance of female reproductive system and female secondary sexual characteristics including breast growth, widening of hips, changes in fat distribution. Estrogen leads to thickening of the uterus lining (endometrium) each month in preparation for implantation of the zygote. FSH stimulates development of ovarian follicles.

Progesterone is secreted by the corpus luteum – the remain of the ovarian follicle following ovulation – in responses to LH. LH causes ovulation. Progesterone involved in formation and maintenance of the endometrium – but not the initial thickening. By the end of the first trimester of a pregnancy, progesterone is supplied by the placenta while the corpus luteum atrophies. Estrogen establishes and progesterone protects the endometrium.

Question 43

Menstrual cycle

Answer 43

From menarche to menopause, estrogen and progestogen levels will rise and fall in cyclic pattern. In response, the endometrial lining will grow and be shed. This is known as the menstrual cycle, and is divided into 4 events: follicular phase, ovulation, luteal phase, menstruation.

1. Follicles mature during the follicular phase (FSH, LH)
2. LH surge at the midcycle triggers ovulation
3. Ruptured follicle becomes corpus luteum, which secretes estrogen and progesterone to build up uterine lining in preparation for implantation; FSH and LH are inhibited
4. If fertilization does not occur, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again.

Question 44

Follicular phase

Answer 44

Begins when the menstrual flow begins, which sheds the uterine lining of the previous cycles. GnRH secretion from the hypothalamus increases in response to the decreased concentrations of estrogen and progestogen, which fall off toward the end of each cycle. The higher concentration of GnRH cause increased secretions of both FSH and LH. These hormones work in in concert to develop ovarian follicles. Follicles produce estrogen, which has negative feedback and causes GnRH, LH, and FSH to decrease. Estrogen stimulates the regrowth of endometrial lining, stimulating vascularization and granularization of the decidua.

Question 45

Ovulation

Answer 45

the release of the ovum from the ovary into the abdominal (peritoneal) cavity. Estrogen can actually have negative and positive feedback on sex hormones. In the follicular phase, after the follicles secrete higher and higher concentrations of estrogen, it eventually reaches a threshold that results in positive feedback on GnRH, LH, and FSH. The surge in LH induces ovulation.

Question 46

Luteal Phase

Answer 46

After ovulation, LH causes the ruptured follicle to form the corpus luteum, which secretes progesterone. Progestogen levels rise, and estrogen remains high. The high levels of progestogen causes negative feedback on GnRH, LH, and FSH preventing ovulation of multiple eggs.

Question 47

Menstruation

Answer 47

Assuming no implantation, the corpus luteum loses its stimulation from LH, progesterone levels decline, and the uterine lining is sloughed off. The reduced levels of estrogen and progesterone removes the block on GnRH so the next cycle can begin.

Question 48

Pregnancy

Answer 48

If fertilization has occurred the resulting zygote will develop into a blastocyte that will implant in the uterine lining and secrete human chorionic gonadotropin (hCG), an analog of LH. This maintains the corpus luteum. hCG is critical because the high levels of estrogen and progesterone secreted by the corpus luteum keep the uterine lining in place. By the 3rd trimester, hCG levels decline as the placenta has grown to sufficient size to secrete enough estrogen and progesterone by itself. These high levels continue to serve as negative feedback on GnRH secretion.

Question 49

Menopause:

Answer 49

With aging, the ovaries become less sensitive to FSH and LH resulting in ovarian atrophy. As estrogen and progesterone levels drop, the endometrium atrophies and menstruation stops. Because the negative feedback on FSH and LH is removed, the blood levels of these hormones rise. Occurs around 45-55.