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Mutations

Mutations . Mutations get passed from one generation to the next when cells copy the mistakes in DNA. Copied mistakes go into daughter cells during cell division. To produce the next generation in sexually reproducing organisms cells experience:. Meiosis. Cell Division.

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Mutations

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  1. Mutations Mutations get passed from one generation to the next when cells copy the mistakes in DNA Copied mistakes go into daughter cells during cell division To produce the next generation in sexually reproducing organisms cells experience: Meiosis

  2. Cell Division Cell Division occurs in two ways: Mitosis produces genetically identical daughter cells Meiosis produces genetically different offspring

  3. Chromosome Changes Most normal cells start with “n” number of pairs of chromosomes n = number of kinds of chromosomes 2n = total number of chromosomes Examples:n2n Onion 4 8 Fly 8 16 Human 23 46 How Many Chromosomes Does It Have? Fathers donate sex cell with half a set of chromosomes = 23 Mothers donate sex cell with half a set of chromosomes = 23 Offspring receives full set of chromosomes = 46/23 pairs Diploid cells – 2n chromosomes Haploid cells – n chromosomes, ½ set

  4. Meiosis Only used to create sex cellscells have n number of chromosomes Human = 23 Onion = 4 Sperm Ovum/Egg

  5. Stages of Meiosis Meiosis occurs over two separate sets of stages, Meiosis 1 and Meiosis 2. Let’s examine how this works with a cell that has 6 chromosomes

  6. Prophase I Homologous chromosomes form, find each other and become tetrads Spindle forms Nucleus breaks up

  7. Metaphase I Tetrads line up in the middle of the cell Spindle fibers attach to centromeres

  8. Anaphase I Tetrads split Homologous chromosomes move to opposite ends of the cell Cell begins cytokinesis

  9. Telophase I Two haploid daughter cells are created Meiosis 2 may begin immediately

  10. Prophase II Spindle fibers form Nucleus breaks apart

  11. Metaphase II Individual Chromosomes line up in the center of the cell Spindle fibers attach to centromeres

  12. Anaphase II Sister chromatids separate Chromatids move to opposite ends of the cell Spindles shorten Cytokinesis begins

  13. Telophase II Cytokinesis ends Four haploid cells are left In most males, all four will become gametes In females, only one will

  14. Gametogenesis Gametogenesis = formation of gametes Gametes: haploid sex cells, contain n number of chromosomes Occurs slightly differently in males and females Spermatogenesis = sperm Oogenesis = egg

  15. Gametogenesis Spermatogenesis Oogenesis X X x x X X x x X x X x X x X x I I I I I I Gametes I I I I I I I I I I 3 nonfunctional polar bodies I I I I I I I I Sperm Egg or Ovum I I I I Fertilization: sperm DNA enters egg, completing the set of chromosomes

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