Lecture 16: Gametogenesis

Question 1

When does oogenesis begin?

Answer 1

In fetal development

Question 2

What is used to perform mitosis in females?

Answer 2

oogonium

Question 3

In between Mitosis and Meiosis I, what do you call the gamete?

Answer 3

oocyte

Question 4

What is special about Meiosis in oogenesis?

Answer 4

It stops at Prophase I and only resumes during a monthly menstrual/ovulation cycle, and pauses at Metaphase II until fertilization. One of the cells from Meiosis I is a large cell, called a secondary oocyte, but the others are small, called polar bodies, and are destroyed.

Question 5

What are the groups that help and promote oogenesis called?

Answer 5

Follicles.

Question 6

Approximately how many primary oocytes are chosen each cycle to continue Meiosis?

Answer 6

Five

Question 7

Does a primary follicle stop developing and support the other follicle?

Answer 7

Yes

Question 8

How many cell layers form around the oocyte and what do they do?

Answer 8

-Two layers and they eventually guide the oocyte to the edge of the ovary, this process is called ovulation.

Question 9

What does the remaining cells of the oocyte become?

Answer 9

They become a hormone secreting structure that remain in the ovaries, which is called corpus luteum.

Question 10

What is the cervix?

Answer 10

An opening from the uterus that can stretch large to let a baby through.

Question 11

What is the size of a uterus and what is it composed of?

Answer 11

About the size of a fist, composed of a thick muscular wall that can stretch a lot.

Question 12

What is the thickening of the lining of the uterus called? and what causes it?

Answer 12

It is called the endometrium, and its caused by hormones.

Question 13

Where does the oocyte go after ovulation?

Answer 13

Moves along the fallopian tubes, waiting to be fertilized.

Question 14

What does the corpus luteum signal after ovulation?

Answer 14

It signals to the uterus to prepare and provide proper nutrients to prepare for a fertilized oocyte.

Question 15

How long does the corpus luteum last for?

Answer 15

A few weeks, after that, it stops supporting the uterine layers, and menstruation begins. Unless, a fertilized egg arrives to the uterus.

Question 16

How many phases are involved in the uterine cycle? name them.

Answer 16

• 4 phases

- Follicular phase, ovulation, luteal phase and menstruation.

Question 17

What happens in the follicular phase?

Answer 17

Follicles release estrogen, which causes the uterine wall to thicken.

Question 18

What happens in ovulation?

Answer 18

The follicle ruptures and develops into a corpus luteum, and progesterone is produced.

Question 19

What happens in the luteal phase?

Answer 19

Progesterone and estrogen are released from the corpus luteum which thickens the endometrium.

Question 20

What happens in menstruation?

Answer 20

Endometrium is sloughed away when the corpus luteum degenerates, and a new cycle begins.

Question 21

List the hormone regulation in a female?

Answer 21

• Hypothalamus -> GnRH -> pituitary gland -> FSH -> blood
• FSH -> ovary -> follicles develop
• Dominant follicle -> estrogen -> stimulate endometrium growth and inhibits the pituitary gland (stops FSH production.
• Estrogen -> pituitary gland -> LH -> ovulation (formation of corpus luteum
• Corpus luteum -> progesterone -> developed endometrium and inhibits pituitary gland

Question 22

Describe the pituitary hormone levels in all phases of the uterine cycle?

Answer 22

• Follicular phase: FSH levels are initially high before being inhibited by estrogen production.
• Ovulation: huge spike of LH levels triggers ovulation.
• Luteal phase: rising level of estrogen and progesterone inhibits FSH and LH
• Menstruation: When the corpus luteum degenerates, estrogen and progesterone levels fall and FSH levels rise.

Question 23

Describe the ovarian hormone levels in all phases of the uterine cycle?

Answer 23

• Follicular phase: Estrogen levels rise as estrogen is produces by developing follicles.
• Ovulation: Estrogen levels drops.
• Luteal phase: Progesterone levels rise with the development of the corpus luteum.
• Menstruation: corpus luteum degenerates, estrogen and progesterone levels fall.

Question 24

Describe the ovarian cycle.

Answer 24

• Follicular phase: FSH causes follicle to mature and produce estrogen.
• Ovulation: an LH surge causes ovulation
• Luteal phase: ruptured follicles form a corpus luteum and secrete progesterone (and some estrogen)
• Menstruation: Corpus luteum degenerates, new ovarian cycle begins.

Question 25

Can problems occur during Meiosis?

Answer 25

Yes, they are called non-disjunction.

Question 26

Describe problems associated with non-disjunction.

Answer 26

It is when chromosomes do not separate as they should.

-Either homologous chromosome in Meiosis I or sister chromatid in Meiosis II.

Question 27

What is the result of non-disjunction?

Answer 27

Egg or sperm with an incorrect number of chromosomes

Question 28

What causes the risk of non-disjunction to increase?

Answer 28

The age of the egg

Question 29

What is Aneuploidy?

Answer 29

When an organism has the incorrect number of chromosomes, happens 1/160 live births have such a defect.

Question 30

are most aneuploidy situations fatal during development?

Answer 30

Yes, this is why the rate of it occurring is so low.

Question 31

What are the most common aneuploidy situations with surviving fetuses?

Answer 31

Chromosomes 13, 18, 21, X and Ys

Question 32

What happens when non-disjunction happens with sex chromosomes?

Answer 32

• If there is a Y, there will be a normal male development. (XYY ends up being normal)
• Only one copy of X is generally used (XXX ends up being a normal female)

Question 33

What happens to a person that have XXY sex chromosomes?

Answer 33

A male, tall stature, slightly feminized physique. Poor beard growth, breast development, small testicles.

Question 34

What happens to a person that has only one X sex chromosome?

Answer 34

A female, short stature, characteristic facial features, constriction of the aorta, poor breast development, underdeveloped gonadal structure, no menstruation.