Oogenesis and spermatogenesis

Question 1

What must happen for pregnancy to occur

Answer 1

there must be the fusion of an egg and sperm in the female reproductive tract.

Question 2

What must the male and female sex cells go through before fertilisation can occur?

Answer 2

They must go through gametogenesis to form mature gametes.

Question 3

How many chromosomes do gametes have?

Answer 3

23

Question 4

What type of egg cells do fetus’ contain?

Answer 4

Germinal oogonia which are diploid

Question 5

How many chromosomes does a diploid cell contain?

Answer 5

46

Question 6

What are germinal oogonia?

Answer 6

Germinal means the earliest stage of development.

Oogonia means diploid ovarian stem cells.

Question 7

What happens to the germinal oogonia?

Answer 7

First there is rapid mitotic proliferation. 1 germ cells form 2 genetically equal cells. The number of germ cells continues to increase to millions. This occurs in the embryonic ovary around the 2nd to 5th month of pregnancy. The number of germ cells can increase up to 7 million and then decreases during the female lifespan. The germinal oocyte must decrease its chromosome number down to 23.

Question 8

In what process does a germinal oocyte decrease its chromosomes?

Answer 8

Meiosis

Question 9

What is rapid mitotic proliferation?

Answer 9

Rapid cell reproduction.

Question 10

What are germ cells?

Answer 10

Reproductive cells in the body.

Question 11

What is an oocyte?

Answer 11

An immature egg.

Question 12

What do germinal oocytes change into and what is the steps for this?

Answer 12

They change into primary oocytes.
In the first meiotic division they change into secondary oocytes with 23 chromosomes, but before this, they are in an arrest period until puberty, so this process to form the secondary oocytes does not happen until then.
Once puberty has occurred, there is the completion of the first meiotic division and this forms 2 unequal cells:
- secondary oocyte
- 1st polar body
This polar body is ejected.

Question 13

What happens after the secondary oocyte is formed?

Answer 13

The secondary oocytes go through a 2nd meiotic division, but this is arrested at metaphase and then released and completed by fertilisation.
In the second meiosis stage another 2 cells are formed:
- ovum (which is now haploid)
- 2nd polar body

Question 14

What does spermatogenesis result in?

Answer 14

It results in 150-275 million spermatozoa being produced per day.

Question 15

When does spermatogenesis begin?

Answer 15

This process begins after puberty in the semiferoustubules of the testes.

Question 16

What is the process after puberty has occurred?

Answer 16

First of all there is mitotic proliferation of the spermatogonia, and this is a continuous process. Spermatogonia have 46 chromosomes and they remain in the mitotic cycle for most of a males reproductive lifetime. Only some enter the meiotic cycle as primary spermatocytes.

Question 17

What happens once the spermatocytes enter the meiotic cycle?

Answer 17

The first meiotic division takes several weeks before 2 secondary spermatocytes are formed. Both of these are the same size and contain 23 chromosomes. Immediately after this has happened, they enter the 2nd meiotic division and 8 hours later 4 haploid spermatids are formed.

Question 18

How long does spermatogenesis generally take?

Answer 18

74 days

Question 19

Compare 8 differences between spermatogenesis and oogenesis:

Answer 19

Spermatogenesis

• occurs entirely in the testes
• equal division of cells
• is involved in gamete production
• 4 produced
• sperm are smaller than the spermatocytes
• Begins at puberty
• Continuously released
• Lifelong but decreases with age.

Oogenesis

• Occurs mostly in the ovaries
• Unequal division of the cytoplasm
• Is not involved in gamete production
• 1 is produced but 2 or 3 polar bodies
• Ova larger than oocytes
• Begins in the foetus (pre-natal)
• Released monthly from puberty
• Terminates with menopause