Oogenesis and spermatogenesis Flashcards
What must happen for pregnancy to occur
there must be the fusion of an egg and sperm in the female reproductive tract.
What must the male and female sex cells go through before fertilisation can occur?
They must go through gametogenesis to form mature gametes.
How many chromosomes do gametes have?
23
What type of egg cells do fetus’ contain?
Germinal oogonia which are diploid
How many chromosomes does a diploid cell contain?
46
What are germinal oogonia?
Germinal means the earliest stage of development.
Oogonia means diploid ovarian stem cells.
What happens to the germinal oogonia?
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.
In what process does a germinal oocyte decrease its chromosomes?
Meiosis
What is rapid mitotic proliferation?
Rapid cell reproduction.
What are germ cells?
Reproductive cells in the body.
What is an oocyte?
An immature egg.
What do germinal oocytes change into and what is the steps for this?
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.
What happens after the secondary oocyte is formed?
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
What does spermatogenesis result in?
It results in 150-275 million spermatozoa being produced per day.
When does spermatogenesis begin?
This process begins after puberty in the semiferoustubules of the testes.
What is the process after puberty has occurred?
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.
What happens once the spermatocytes enter the meiotic cycle?
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.
How long does spermatogenesis generally take?
74 days
Compare 8 differences between spermatogenesis and oogenesis:
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
