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DNA

DNA. Why do you look a little like your mother a little like your father? Why do you have traits that your grandparents had but your parents didn’t?. Meiosis. Sexual Reproduction. Purpose. To allow individuals to pass on half of their chromosomes to offspring

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DNA

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  1. DNA • Why do you look a little like your mother a little like your father? • Why do you have traits that your grandparents had but your parents didn’t?

  2. Meiosis Sexual Reproduction

  3. Purpose • To allow individuals to pass on half of their chromosomes to offspring • In vertebrate animals it produces the gametes (sperm and egg cells)

  4. Homologous Chromosomes • You have 2 versions of each chromosome • They contain slightly different versions of the same genes, called alleles • You inherit one from each parent

  5. Diploidy • For most genes you have 2 alleles (i.e. brown eye color proteins and green eye color proteins . • Sometimes you express only one of them and sometimes both • But you only pass one of them on to each sperm or egg cell. • Each sperm or egg randomly receives one allele or the other

  6. Meiosis • Produces cells that contain only 1 copy of each homologous chromosome • Also pass on one of the sex chromosomes • So each gamete contains 22 autosomal chromosomes and an X or Y chromosome

  7. Steps of Meiosis • Very similar to mitosis, except they happen twice

  8. Meiosis I • Instead of the replicated chromosomes being separated – the homologous chromosomes get pulled apart

  9. Meiosis II • Similar to mitosis, except the cell begins with only half the chromosomes

  10. Why Sexual Reproduction? • Because diversity is good! • Increases chances that our species will survive • Meiosis produces an incredible amount of diversity

  11. How? • You can get either 1 of your mother’s pair of chromosomes for all 23 • So you can get 1A2A3A…23A, 1B2A3A..23A, 1A2B3A…23A- basically a whole lot of combinations • You get genes from your mother and your father- new combinations can be beneficial

  12. Reproductive Strategies • Differ greatly between groups of species • Many asexual species or species whose sexual reproduction does not involve male/female roles

  13. In Humans • The ovaries/testes contain cells called germ cells which undergo meiosis • Produce sperm and egg (23 chromosomes) • Sperm and egg fuse in fertilization forming a zygote

  14. Bacteria • Simply divide asexually • No mixing of genes- offspring are identical

  15. Single Celled Eukaryotes • Often divide simply by mitosis • All offspring are identical

  16. Haplodiploidy • In bees, wasps and ants unfertilized eggs develop into males • Only half one set of chromosomes • Fertilized eggs develop into females • Have 2 sets of chromosomes

  17. Hermaphroditic Eukaryotes • No male/female division – individuals can make both sperm and egg • Most plants • Many snails and other solitary creatures • Still require other individuals to reproduce with (usually) http://www.youtube.com/watch?v=FhVi4Z6CjZk

  18. Sequential Hermaphroditism • In a group of clownfish only one individual is the female and one is the male • When the female dies, the male grows and turns into the female • Another fish can then assume the role of the male If Nemo is lucky he might one day become a man… then a woman.

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