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Spermatogenesis & Oogenesis
Pg
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Spermatogenesis Occurs in the seminiferous tubules of the testes
the formation of sperm Takes 65 to 70 days
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Spermatogenesis Overview
Begins with one cell Which becomes two Finally four
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Primary Spermatocytes
These are the basic cells, where process begins Diploid Produced continuously by mitosis
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Sperm cells Also haploid, are produced when secondary spermatocytes divide
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Question: T/F: A woman is born with all the eggs she will ever have
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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
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7th Inning Stretch Launch
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Oogenesis Occurs in the ovaries Formation of oocytes, eggs
Begins prior to birth! Spans all of pre-reproductive & reproductive life
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Oogenesis Overview Begins with one cell Which becomes two
Then finally, four
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Primary Oocyte These are present at birth
Stay dormant until sometime after puberty..things get kinky Diploid (2n) 46 chromosomes
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First Polar Body Results from meiosis I Smaller (has less cytoplasm)
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Secondary Oocyte Released by ovulation Happens roughly every 28 days
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Fertilization Sperm penetrates secondary oocyte Triggers meiosis II
Oocyte’s nucleus divides One nucleus stays, combines with sperm’s nucleus Other nucleus leaves
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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?
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Question What cell division process is used in spermatogenesis?
In oogenesis? How do they differ?
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Answer Both spermatogenesis and oogenesis use meiosis
Spermatogenesis needs many, many parent cells—provided by mitosis
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