Prefertilization Events

Question 1

Sexual reproduction

Answer 1

• female + male gametes unite at fertilization
  A. Gametes
• descendants of primordial germ cells, observed in wall of yolk sac ⇒ migrate into gonads
• produced by gametogenesis
  B. Gametogenesis
• process of cell division- meiosis

Question 2

Chromosomes

Answer 2

A. Structure
- 2 arms + centromere
- after meiosis 1 ⇒ chromatids attached to centromere
B. Ploydi and N number
- ploidy= number of chromosomes in cell
- N number= amount of DNA in cell
- normal cell 46 chromosomes, 2N
- 23 homologus pairs⇒ 1-22 autosomal, 23 sex chromosome
- gametes: 23 chromosomes, 1N

Question 3

X chromosome

Answer 3

• normal female have 2 X chromosomes

- 1 X chromsome inactivated ⇒ random selection, called Barr body

Question 4

Y chromsome

Answer 4

• male sexual differentiation

- nomral male XY

Question 5

Meiosis

Answer 5

• cell division in production of gametes

- 2 divisions ⇒ 4 gamete cells, each have 23 chromosomes, 1 N

Question 6

Meiosis 1

Answer 6

1. DNA replication⇒ primary gametocyte
2. Synapsis⇒ pairing 46 chromosomes
3. Crossover ⇒ chromatid segments exchanged
4. Alignment ⇒ align at metaphase plate
5. Disjunction ⇒ chomosomes separate from each others, centromeres do not split
6. Cell division ⇒ 2 secondary gametocytes

Question 7

Meiosis 2

Answer 7

1. Alignment ⇒ 23 chromosomes align in metaphase plate
2. Disjunction ⇒ separation, controllers split
3. Cell division ⇒ 4 gametes

Question 8

Oogenesis

Answer 8

1. Primordial germ cells ⇒ ovary ⇒ differentiate to oogonia by mitosis
2. Oogonia ⇒ primary oocyte ⇒ enter meiosis 1 by undergoing DNA replication
3. All primary oocytes formed by 5 month of fetal life
4. Primary oocytes remain in prophase in meiosis 1 until puberty
5. After puberty primary oocyte completes meiosis 1 ⇒ secondary oocyte + polar body
6. Secondary oocyte enters meiosis 2 ⇒ ovulation ⇒ stays in meiosis 2 until fertilization

Question 9

Spermatogenesis

Answer 9

1. Primordial germ cells ⇒ gonads ⇒ remain dormant until puberty
2. At puberty primary germ cell ⇒ mitosis to spermatogonia
3. Spermatiogonia ⇒ primary spermatocytes enter meios 1 by DNA replication
4. Primary spermatocyte ⇒ secondary spermatocyte by meiosis 1
5. Secondary spermatocytes ⇒ spermatids by meiosis 2

Question 10

Spermiogenesis

Answer 10

• maturation of spermatids ⇒ spermatozoa
• inclute formation of acrosome, condensation of nucleus + formation of head, neck and tail
• total time of sperm formation: 64 days

Question 11

Capacitation of Sperm

Answer 11

• reversible process where mature sperm develop capacity to fertilize secondary oocyte
• occurs in female reproductive tract- takes 7 h
  1. unmasking of glycosyltransferases on sperm cell membrane
  2. removal of surface-coating proteins from seminal fluid