Genetics Lesson 03

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Gamete Formation in Animals
Spermatogenesis
Oogenesis
• Both Spermatogenesis and Oogenesis involve
the process of meiosis, but they take place in
different ways
Spermatogenesis
• The process of creating sperm.
• Takes place in the Testes of most animals.
• The process begins with a diploid (2n) cell
called a Spermatogonium.
• At the beginning of puberty, the
Spermatogonia reproduce through Mitosis.
Spermatogenesis
Spermatogenesis
• These diploid cells then undergo Meiosis to
form 4 Haploid (n) cells.
• After Meiosis II, the new haploid cells undergo
a final set of developmental stages.
• Afterwards, the cells are mature Sperm.
Oogenesis
• The process of creating egg cells
• Takes place in the ovaries of most animals
• The process begins with a diploid (2n) cell
called an oogonium.
• Oogonia reproduce by mitosis before birth
and begin meiosis, but stop at Prophase I.
Oogenesis
• There is an uneven distribution of cytoplasm after
meiosis I.
• The cell with most of the cytoplasm continues
through meiosis I and II to form an egg.
• The other products are called polar bodies and
degenerate.
• Meiosis II is not completed unless the egg is
fertilized by a sperm cell.
Multiple Births
Errors During Meiosis
Cri du Chat
Klinefelters
Down’s Syndrome
Turner Syndrome

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