kuliah 6. gametogenesis
DESCRIPTION
FKTRANSCRIPT
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