Gametogenesis

Question 1

What does meiosis accomplish?

Answer 1

1. 4 daughter haploid germ cells, recombination occurs (genetic variation),
2. Each cell has of 1 copy of each chromosome

Question 2

What are the differences between meiosis in sperm and eggs?

Answer 2

Sperm - symmetry of meiotic separations. Metaphase plate is always in the center of the cell.

Eggs - Asymmetric divisions. Creates 3 polar bodies and one egg. Metaphase plate is located on one side of the cell.

Question 3

What is a polar body?

Answer 3

Result of meiotic divisions, are barren cells that contain a haploid genome.

Question 4

What is the basic structure of the seminiferous tubule in mammals?

Answer 4

Spermatogonium are around the exterior of the tube. The developing spermatids align adjacent to sertoli cells and have their tails facing the lumen of the tubule.

Question 5

What is the function of the Sertoli cells?

Answer 5

Provide nutrients and “nurse” the sperm

Question 6

Why are Type A1 spermatogonia considered stem cells?

Answer 6

Type A1 spermatogonia are non-differentiated and are constantly producing new Type A1 cells which will be made to make more A1 cells. They are also used to make type A2 cells, which are then further differentiated.

Question 7

What specializations are present in sperm that relate to their function? (For example, what is the acrosome? How does the flagella work?)

Answer 7

1. Centriole organizes in center, which grows microtubules
2. Acrosome is made from GA and carries enzymes that degrade egg outer membrane
3. Flagella have abundant mitochondria and are made of microtubules that propel the cell forward by a spinning or undulating motion.

Question 8

What is the structure of the ovary?

Answer 8

The ovaries contain eggs used for reproduction. The eggs are maintained within follicles. The follicles grow and mature and become grafian follicles. This mature follicle eventually binds to the outer membrane and ruptures releasing the secondary oocyte. Old follicles mature into a corpus luteum, which produces fats and progesterone as it heals and then is eventually degenerated.

Question 9

What is the corpus luteum, and what is its function?

Answer 9

1. Develops from the follicular cells surrounding an ovarian follicle
2. The corpus luteum produces progesterone, which serves as a sort of master regulator of the pregnancy and serves to inhibit the release of hormones from the hypothalamus and AP gland and induce the Uterine Lining to prepare for implantation.

Question 10

GnRH

Answer 10

1. Gonadotropin releasing hormone
2. From Hypothalamus, to AP
3. Causes release of FSH & LH

Question 11

FSH & LH (Female)

Answer 11

released from AP & act on ovary to induce ovulation

Question 12

Estrogen

Answer 12

released from ovary, causes increase in GnRH from hypothalamus, and resulting LH and FSH release from AP. Positive feedback loop alone, negative with progesterone.

Question 13

Progesterone

Answer 13

Acts with estrogen to cause a negative feedback loop which slows the release of GnRH from HT, and FSH and LH release from AP, and prevents induction of ovulation from ovary.

Question 14

FSH (male)

Answer 14

causes spermatogenesis

Question 15

LH (male)

Answer 15

causes production of testosterone which serves as a negative feedback loop on GnRH release

Question 16

Testosterone

Answer 16

released from testes after LH stimulation and serves as a negative feedback loop on GnRH in the hypothalamus. Also has roles in primary and secondary sex characteristics

Question 17

What is the role of human chorionic gonadotropin in maintaining pregnancy?

Answer 17

hCG causes a positive feedback loop that helps maintain the pregnancy. It helps by increasing progesterone production of the corpus luteum and supports endometrium, inhibits contractions, and firms the cervix.

Question 18

What is the molecular mode of action of the standard birth control pill?

Answer 18

estrogen and progestin (synthetic progesterone) – works to prevent ovulation, increase cervical mucus to prevent sperm travel, and alters the uterine lining to prevent implantation

Question 19

Plan B

Answer 19

high levels of progestin (synthetic Progesterone) – causes same effects as standard birth control an induces menses

Question 20

RU486

Answer 20

Binds to progesterone receptor and has inhibitory action – induces menses, contractions and dilation of the cervix

Question 21

How do we trigger superovulation for in vitro fertilization?

Answer 21

By Increasing LH and FSH, we cause superovulation which causes multiple follicles to mature an increases the likelihood of pregnancy

Question 22

At what stage(s) of meiosis are mammalian oocytes/eggs arrested?

Answer 22

Second Metaphase

Question 23

How do cdks and cyclins regulate the cell cycle?

Answer 23

CDKs act to active Maturation Promoting Factor (MPF), which initiates 1st meiotic metaphase. CDK levels are constant, but the levels of active CDK vary with the amount of cyclins that are present. CDK activation causes cyclin degredation to prevent constant CDK activation.

Question 24

Describe the meiotic cycle of the egg with respect to the control of MPF.

Answer 24

MPF activation serves to activate the 1st meiotic metaphase to allow for egg maturation to occur. LH triggers MPF activation after puberty.