Meiosis and Sexual Reproduction

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Meiosis and Sexual Reproduction

• 10.1 Overview

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What are homologous chromosomes?

• Found in diploid cells only
• Identical order of genes
• Alleles (versions of genes) may vary

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What is meiosis?

• Chromosomal reductionproduction of gametes
• Two stages
• Meiosis I
• Meiosis II
• Produces 4 daughter cells
• daughter cells are NOT identicalsee why on the
  next slide
• haploid cells
• Compare to mitosis

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Why are daughter cells not identical?

• Meiosis increases genetic variation
• Two ways
• Crossing over
• Synapse
• Bivalent
• During prophase I
• Independent assortment
• During metaphase I

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Why is there sexual reproduction?

• Genetic variation
• Disease resistance
• Why create gametes?
• Diploid number would double every generation
  otherwise
• Haploid gametes maintain diploid number

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What else increases genetic variation?

• Fertilization
• Haploid gamete haploid gamete diploid zygote

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Meiosis and Sexual Reproduction

• 10.2 Meiosis I

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What happens in Meiosis I?

• Reduction of chromosomal number
• 2n (1 cell) ? 1n (2 cells)
• Crossing over
• Independent assortment
• Same stages as mitosis
• Key point separation of HOMOLOGOUS CHROMOSOMES,
  not sister chromatids

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Note At Anaphase I, the cells are now HAPLOID
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Meiosis and Sexual Reproduction

• 10.3 Meiosis II

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What happens in Meiosis II?

• Just before interkinesis (like interphase)
• Separation of sister chromatids
• Basically the same as mitosis except cells are
  haploid, not diploid

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What happens in Meiosis II?
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Meiosis and Sexual Reproduction

• 10.4 Comparisons and gamete production

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How do mitosis and meiosis compare?
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What is spermatogenesis?

• Production of spermatids
• Spermiogenesis is conversion to sperm cells

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What is oogenesis?

• Manufacture of egg cells
• Polar bodies
• Meiosis II delayed until fertilization