Sexual reproduction in mammals

Question 1

Germ cell

Answer 1

diploid cells which give rise to gametes through meiosis

Question 2

Polar body

Answer 2

a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have ability to be fertilised

Question 3

Germinal epithelium

Answer 3

a single layer of cells that undergoes regular mitosis, producing other cells

Question 4

Gametogenesis

Answer 4

process of gamete production
- the female and male gametes are produced in organs called gonads

Question 5

what is the female gonads called ?

Answer 5

ovaries - produces ova

Question 6

what is the male gonads called ?

Answer 6

testes - produces spermatozoa

Question 7

Spermatogenesis

Answer 7

1. germ cells divide several times by mitosis to form spermatogonia
2. spermatogonia grow without further division to form primary spermatocytes
3. primary spermatocytes undergo the first meiotic division to form secondary spermatocytes
4. secondary spermatocytes undergo the second meiotic division to form spermatids
5. spermatids differentiate and grow to form mature spermatozoa

Question 8

Oogenesis

Answer 8

1. germ cells divide several times by mitosis to form oogonia
2. only one oogonium continues to grow to form a primary oocyte
3. the first meiotic division forms one secondary oocyte and one polar body
4. the second meiotic division of the secondary oocyte forms one haploid ootid and one polar body - than forms two more polar bodies
5. degenerate and die as the ootid develops

Question 9

what does the ovum contain ?

Answer 9

• zona pellucida
• haploid nucleus
• cortical granules
• follicle cells

Question 10

Zona pellucida

Answer 10

protective coating that the sperm have to penetrate in order for fertilisation to occur
main purpose: to prevent polyspermy

Question 11

Haploid nucleus - ovum

Answer 11

full set of chromosomes is restored at fertilisation

Question 12

Cortical granules

Answer 12

release substances which cause the zona pellucida to harden, forming a tough fertilisation membrane

Question 13

Follicle cells

Answer 13

forms protective coating around the egg

Question 14

Spermatozoa - key features

Answer 14

• mitochondria
• acrosome
• haploid nucleus

Question 15

Mitochondria

Answer 15

provide energy for rotation of the flagellum which enables the cell to move

Question 16

Acrosomes

Answer 16

contain digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg

Question 17

Haploid nucleus - spermatozoa

Answer 17

allows the restoration of the full set of chromosomes at fertilisation

Question 18

Process of fertilisation

Answer 18

1. the sperm head contacts the zona pellucida and the acrosome reaction occurs
2. the sperm head fuses with the cell membrane of the egg cell, thus allowing the sperm nucleus to enter the egg cell
3. the cortical reaction occurs
4. nuclei fuse and a full set of chromosomes is restores, thus forming a diploid zygote

Question 19

Acrosome reaction

Answer 19

• acrosome swells and fuses with membrane of secondary oocyte
• releases hydrolytic enzymes which hydrolyse the zona pellucida

Question 20

Cortical reaction

Answer 20

• head of sperm is engulfed and this causes by microvilli to increase in calcium ions
• cortical granules fuse with the membrane
• hardens - prevents polyspermy

Question 21

Following fertilisation…

Answer 21

• the zygote is moved down the oviduct by ciliary action
• the zygote will undergo several mitotic divisions to transform a single zygote to form a solid ball of cells - cleavage
• At day 3, cleavage has transformed a single zygote to form a solid ball cells called morula
• At day 4, the solid ball of called morula have now transformed into a blastocyst

Question 22

Blastocyst

Answer 22

• inner cell mass called blastomeres
• surrounding outer layer called the trophoblast
• a fluid filled cavity called the blastocoele