Spermatogenesis & Oogenesis Pg. 103-104

Spermatogenesis Occurs in the seminiferous tubules of the testes the formation of sperm Takes 65 to 70 days

Spermatogenesis Overview Begins with one cell Which becomes two Finally four

Primary Spermatocytes These are the basic cells, where process begins Diploid Produced continuously by mitosis

Sperm cells Also haploid, are produced when secondary spermatocytes divide

Question: T/F: A woman is born with all the eggs she will ever have

Answer: Technically not true! A woman is born with all the primary oocytes she will ever have They will become eggs later This probably is the reason why chances of Down’s syndrome increase with mother’s age

7th Inning Stretch Launch

Oogenesis Occurs in the ovaries Formation of oocytes, eggs Begins prior to birth! Spans all of pre-reproductive & reproductive life

Oogenesis Overview Begins with one cell Which becomes two Then finally, four

Primary Oocyte These are present at birth Stay dormant until sometime after puberty..things get kinky Diploid (2n) 46 chromosomes

First Polar Body Results from meiosis I Smaller (has less cytoplasm)

Secondary Oocyte Released by ovulation Happens roughly every 28 days

Fertilization Sperm penetrates secondary oocyte Triggers meiosis II Oocyte’s nucleus divides One nucleus stays, combines with sperm’s nucleus Other nucleus leaves

Down’s Syndrome Much more likely with older moms 3 copies of chromosome 21 Caused by non-disjunction of chromosomes Could this occur in meiosis II? Why are mistakes more likely with older oocytes?

Question What cell division process is used in spermatogenesis? In oogenesis? How do they differ?

Answer Both spermatogenesis and oogenesis use meiosis Spermatogenesis needs many, many parent cells—provided by mitosis