Oogenesis Melissa Nishihama

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 300-500 will mature to secondary oocytes

1. MITOSIS 2. 3. Meiosis I Meiosis II

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)

Already born with ~1million primordial follicles 1. Stopped @ 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 300-500 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

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

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

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

References http://campus.udayton.edu/~INSS/Dillon230/LECTHELP-2/2spermatogenesis_vs.htm https://www.premedhq.com/mitosis-vs-meiosis http://womenshealth.about.com/cs/ovarianconditions/a/yrovrisovuovads_2.htm http://molehr.oxfordjournals.org/content/17/5/273.full