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Biology 102

Biology 102. Cellular reproduction (cont.2). Lecture outline. Sexual vs. asexual reproduction Advantages and Disadvantages Steps and details of meiosis Errors in meiosis (briefly). Sexual vs. asexual reproduction. Advantages of asexual reproduction: Can reproduce on own.

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Biology 102

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  1. Biology 102 Cellular reproduction (cont.2) Chapter 1

  2. Lecture outline • Sexual vs. asexual reproduction • Advantages and Disadvantages • Steps and details of meiosis • Errors in meiosis (briefly) Chapter 1

  3. Sexual vs. asexual reproduction • Advantages of asexual reproduction: • Can reproduce on own. • Why an advantage? • ALL of your genes carried on to offspring. • Allows for rapid production of offspring. • Relatively "cheap": each replication produces new individuals. • Disadvantages of asexual reproduction: • No genetic recombination • No chance to create offspring that might deal better with new situations • Genes dispersed in exactly same "package“ Chapter 1

  4. Sexual vs. asexual reproduction • Advantages of sexual reproduction • Genetic recombination • Potential for offspring to deal better with novel situations than parent type • Your siblings aren't clones of each other. One genetic combinations might do markedly better • Disadvantages of sexual reproduction • Must find compatible partner (difficult in some habitats) • Each offspring carries only 50% of your genes, not 100% • New combination could be less effective than what you have! • Must produce many gametes… Chapter 1

  5. Meiosis I Homologous chromosomes exchange DNA & align on equator Homologous chromosomes pair and cross over Prophase I Metaphase I Chapter 1

  6. Crossing Over • Review steps • What is accomplished? Chapter 1

  7. Meiosis I Homologous chromosomes exchange DNA & align on equator Homologous chromosomes move to opposite poles Homologous chromosomes pair and cross over Telophase I Prophase I Metaphase I Anaphase I Chapter 1

  8. Metaphase I Alignment Scenarios • Note side-by-side alignment • Note independent assortment of chromosomes Chapter 1

  9. Meiosis II Similar to Mitosis FourHaploidCells Prophase II Metaphase II Anaphase II Telophase II Chapter 1

  10. Errors in meiosis • Down Syndrome • Chromosome pair 21 doesn’t split up (Metaphase 1) • Egg has three homogous chromosomes • Why more prevalent in older women? • Meiosis stops in Prophase 1 until ovulation… • XXY or XYY • Similar mechanism, but with sex chromosomes • Effects Chapter 1

  11. Meiosis vs. Mitosis:Comparison of Stages Chapter 1

  12. Meiosis vs. Mitosis:Comparison of Spindles Meiosis: Duplicated chromosomes with one kinetochore; Paired homologues go to opposite poles. Mitosis: Duplicated chromosomes with two kinetochores; Unpaired homologs split between sister chromatids, which go to opposite poles. Chapter 1

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