1. Oogenesis
Melissa Nishihama

2. What is Oogenesis? Production of female gametes -Haploid egg cells (n)
Process beings during fetal period (intrauterine)
- starts developing primordial follicles between 4-8 weeks.
Females already born with ~1 mill primordial follicles
- ~1/2 are absorbed during childhood (leaving ~300,000 to develop)
- most actually die off, about will mature to secondary oocytes

3. 1.
MITOSIS 2. 3.
Meiosis I
Meiosis II

4. Mitosis vs Meiosis Review:
Sexual reproduction
Asexual reproduction
Produces genetically different daughter cells
-chromosomes reduced(n)
Produces genetically identical daughter cells (2n)
1 division -> 2 diploid
2 division-> 4 haploid
(for spermatogenesis)
2 divisions-> 1 haploid
3 polar bodies
(For oogenesis)

5. Already born with ~1million primordial follicles1.
prophase of meiosis I
Multiplication & growth
Each month from puberty to menopause 1. 2. 3.
Already born with ~1million primordial follicles
However most die off, so only about will actually mature into secondary oocytes
During childhood, most are absorbed
By the time they reach puberty ~300,000 follicles remain
Don’t make any more new primary oocytes after birth

6. Each month 15-20 primary oocytes mature in ovaries..
BUT only one is selected to undergo MEIOSIS I --> secondary oocyte and ovulated. (rest are reabsorbed)
If secondary oocyte not fertilized, flushed out with menstruation
Into fallopian tube
ovulation
1 oocyte > 2 oocyte > Ovum (fertilized)
MEIOSIS I
MEIOSIS II
~14 days

7. Secondary oocyte released
Follicular Development: 2n
Polar body
Primary oocyte n
Meiosis I
Secondary oocyte
ovum
Meiosis II
fertilization n n
Fallopian tube
Secondary oocyte released

8. Oogenesis vs Spermatogenesis
Begins 4- 8 weeks intrauterine, ends at menopause
Begins at puberty, ends at death
One oogonium produces only one ovum
One spermatogonium produces four sperm cells
- Unequal meiotic division lead to unequal cytoplasmic divisions (polar bodies)
Millions produced at a time
Only one ovum produced monthly

9. References