Meiosis and Gamete Formation

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Meiosis and Gamete Formation
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3 Types of Cell Division

• 1. Binary fission-cell division in prokaryotes
• 2. Cell Cycle (with Mitosis)-cell division in
  eukaryotes to form new somatic cells
• 3. Meiosiscell division in eukaryotes to form
  gametes (egg and sperm)

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How are reproductive cells formed? MEIOSIS

• Meiosis--cell division that produces reproductive
  cells called gametes (egg and sperm)
• 1 REPLICATION AND 2 DIVISIONS
• 46 chromosomes -------------? 23 chromosomes
• diploid (pairs) MEIOSIS haploid (no
  pairs)
• 1 somatic (body) cell 4 gametes
  (sex cells)
• START END
• Only one set of chromosomes in gametesno longer
  in pairs

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Body Cells vs. Reproductive Cells

• SOMATIC CELLS ----? GAMETES
• DIPLOID MEIOSIS HAPLOID

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Think About it!!!!

• With meiosis to go from 46 ? 23 chromosomes
• you end up with
• your moms egg (23 chromosomes)
• your dads sperm (23 chromosome)
• you (46 chromosomes)
• WITHOUT MEIOSIS to go from 46 ? 23 chromosomes
  then it would be
• your moms egg (46 chromosomes)
• your dads sperm (46 chromosomes)
• 92 AND NO YOU!!!!!!!!!!

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Think About it!!!!

• With meiosis to go from 46 ? 23 chromosomes
• you end up with
• your moms egg (23 chromosomes)
• your dads sperm (23 chromosome)
• you (46 chromosomes)
• WITHOUT MEIOSIS to go from 46 ? 23 chromosomes
  then it would be
• your moms egg (46 chromosomes)
• your dads sperm (46 chromosomes)
• 92 AND NO YOU!!!!!!!!!!

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HAPLOID GAMETE (EGG) 23 CHROMOSOMES
FIRST DIPLOID CELL OF BABY 46 CHROMOSOMES IN
PAIRS!!!!
HAPLOID GAMETE
(SPERM) 23 CHROMOSOMES
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What are reproductive cells?

• EGGS--In females, body cells in the ovaries
  called oogonium undergo meiosis to form eggs.
• SPERM--In males, body cells in the testicles
  called spermatogonium undergo meiosis to form
  sperm.

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Spermatogenesis (Meiosis in Males)
Spermatogonium
46
23
23
23
23
SPERM
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Oogenesis (Meiosis in Females)
Oogonium
46
Egg
Polar Bodies (not functional)
23
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Crossing-Over

• Crossing-over during meiosis results in pieces of
  chromosomes being exchanged.
• This leads to great genetic diversity of the egg
  and sperm that are produced.

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