Reproduction and Meiosis

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Reproduction and Meiosis
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Reproduction

• Reproductionthe process of producing offspring
• Asexualone parent, offspring are genetically
  identical to parent
• Budding, fission, fragmentation, parthenogenesis
• Sexualtwo parents, offspring genetically
  different from parents
• Parents produce gametes
• Femalesegg
• Malessperm
• Two gametes combinefertilization produces first
  cell called the zygote
• Offspring will have traits of both parents

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Homologous Chromosomes

• Each species has a characteristic number of
  chromosomes
• Humans46 dogs78 fruit flies8
• Chromosomes come in pairshomologous chromosomes
• Chromosomes with the same size, shape, and carry
  the codes for the same genes
• Each chromosome in a homologous pair comes from
  one of the parents
• In humans, 23 chromosomes come from mom and 23
  from dad

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Meiosis

• Form of cell division that produces 4 daughter
  cells with half the number of chromosomes as the
  parent cell
• 2 distinct stages
• Meiosis I
• Prophase I, Metaphase I, Anaphase I,
• Telophase I
• Meiosis II
• Prophase II, Metaphase II, Anaphase II,
• Telophase II

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Meiosis I

• Prophase I
• Chromosomes condense
• Homologous chromosomes pair up
• Crossing over
• Chromatids exchange genetic material
• Increases genetic variability

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Meiosis I

• Metaphase I
• Homologous chromosomes line up along equator of
  cell
• Anaphase I
• Homologous chromosomes move apart, pulled by
  spindle fibers
• Telophase I
• Cytoplasm divides, resulting in two cells with
  the same number of chromosomes as parent

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Meiosis II
Prophase II
Metaphase II
Telophase II
4 different haploid cells
Anaphase II
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Results of Meiosis
Gametes (egg sperm) form Four haploid
cells with one copy of each chromosome One
allele of each gene Different combinations of
alleles for different genes along the chromosome
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Mitosis vs Meiosis
Mitosis Meiosis
Number of divisions 1 2
Number of daughter cells 2 4
Genetically identical? Yes No
Chromosome Same as parent Half of parent
Where Body cells Sex cells
When Throughout life At sexual maturity
Role Growth and Repair Sexual Reproduction
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Gamete Production

• Gametes have half the number of chromosomes of
  the organism
• Sperm (23 chromosomes) Egg (23 chromosomes)
  Human (46 chromosomes)
• Diploid (2n)
• A cell with two of each chromosome, which are in
  pairs FULL set
• Haploid (n)
• A cell with only one of each chromosome half set

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Gamete Production Sperm

• Occurs in the testes
• Two divisions produce 4 spermatids
• Spermatids mature into sperm
• Men produce about 250,000,000 sperm per day

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Gamete Production Egg

• Occurs in the ovaries
• Two divisions produce 3 polar bodies that die and
  1 egg
• Polar bodies die because of unequal division of
  cytoplasm
• Immature egg called oocyte
• Starting at puberty, one oocyte matures into an
  ovum (egg) every 28 days