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MEIOSIS

MEIOSIS. Sperm & Eggs & Variation!. Sexual Reproduction requires Cells Made by Meiosis. Genome. Genes. Heredity. Sexual reproduction. Chromosomes. Karyotype. In humans. e.g. 23 chromosomes in haploid 2n = 46; n = 23 2 n = 2 23 = ~ 8 million possible combinations!. Karyotyping.

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MEIOSIS

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  1. MEIOSIS Sperm & Eggs & Variation!

  2. Sexual Reproduction requires Cells Made by Meiosis

  3. Genome

  4. Genes

  5. Heredity

  6. Sexual reproduction

  7. Chromosomes • Karyotype

  8. In humans e.g. 23 chromosomes in haploid 2n = 46; n = 23 2n = 223 = ~ 8 million possible combinations!

  9. Karyotyping

  10. HomologOUs CHROMOSOMES

  11. HomologOUs CHROMOSOMES

  12. In humans …

  13. Chromosome numbers All are even numbers – diploid (2n) sets of homologous chromosomes.

  14. Meiosis – key differences from mitosis

  15. Crossing over Chiasmata Synapsis Recombinantchromosomes.

  16. Animation

  17. Meiosis I • Prophase 1 • Metaphase 1

  18. Meiosis I • Anaphase 1 • Telophase 1

  19. Meiosis II Second division of meiosis: Gamete formation • Prophase 2 • Metaphase 2

  20. MEIOSIS II • Anaphase 2 • Telophase 2

  21. Mitosis vs. meiosis

  22. Meiosis creates genetic variation • Mitosisproduces daughter cells identical to parent cell (2n to 2n) • Meiosis results in genetic variation • Shuffling • Crossing over

  23. Independent assortment

  24. Independent assortment Number of combinations: 2n e.g. 2 chromosomes in haploid 2n = 4; n = 2 2n = 22 = 4 possible combinations

  25. Crossing over Chiasmata Synapsis. Recombinantchromosomes.

  26. HOW SEX IS DETERMINED IN HUMANS • Females don’t have a Y chromosome • Y chromosome is not necessary.

  27. SEX DETERMINATION IN OTHER SPECIES

  28. Random fertilization At least 8 million combinations from Mom, and another 8 million from Dad … >64 trillion combinations for a diploid zygote!!!

  29. Meiosis & sexual life cycles • Life cycle • Somaticcells • Gametes

  30. Meiosis & sexual life cycles Generalized animal life cycle

  31. principles of Hereditysummary of Mendel’s Principles • The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.

  32. Summary of Mendel’s Principles • The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. • In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others recessive.

  33. Summary of Mendel’s Principles 3. In most sexually reproducing organisms, each adult have two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed.

  34. Summary of Mendel’s Principles 3. In most sexually reproducing organisms, each adult have two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed. 4. The alleles for different genes usually segregate independently

  35. Sex is costly! • Large amounts of energy required to find a mate • Infection • Genetic costs: • Males contribute little to rearing offspring.

  36. genetic diversity: • Linked Genes:

  37. NONDISJUNCTION

  38. Down's Syndrome

  39. TOO MANY OR TOO FEW CHROMOSOMES

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