GAMETOGENESIS

Conversion of germ cells into male and female gametes

Gametogenesis

• Female: Oogenesis– Primordial germ cells:1700 germ cellmigrate

to ovariumoogonia– Mitosis– About 7 million cells– Prophase miosis I– Most oogonis fail to matureprimary oosit– About 2 million oosit remain– 99% fail to maturedegenerate

• At puberty:300.000

• At menopause: a few are present

• Prophase of meiotic I:40-50 yrs– Damage– High incidence of genetic abnormality:

nondisjunction

Oogenesis

• Primordial germ cell

• Oogonia: mitosis

• Primary oosit– Meiosis I begin– DNA replication– Pairing of homolog chromosom– Cross over between chromated– Arrested in prophase I: for futher development

Sexual maturity

• Egg maturation• Cytoplasm devide asymetrically

– Oosit II + polar body

• Meiosis II– Chromosom haploid– Ovum– Polar body– Completed after fertilization

In oogenesis

• Oocyt produced in early embryogenesis

• Primary oosit produce only one mature egg ( the other: polarbodydegenerated )

• Cytokinesis are completed

In spermatogenesis

• Germ cell enter meiosis continually from the time of sex maturation

Crossover

• Meiosis

• Interchange of chromatid segments

• Chiasma

• Result:– Genetic variability, random distribution of

homologous chromosomes to daugter cells