STUDY GUIDE Ch13_Meiosis + sex determination 1. Define haploid and diploid. Which cells in the body are diploid and which ones are haploid? 2. Define homologous chromosomes 3. Mention the reasons why meiosis is necessary 4. Mention the different stages of meiosis 1 and 2, state the main things that happen on each one Use question 11 of the MITOSIS study guide to refresh your memory about some of the important events for both mitosis and meiosis. For each one of these events… explain if they happen in meiosis 1 or 2, or both. Now, specifically for meiosis: In what meiosis (1 or 2) and stages is genetic variability produced? In what meiosis (1 or 2) do cells become haploid (N)? During what meiosis (1 or 2) you will have homologous chromosomes present in the same cell? How will prophase 1 be different from prophase 2? How will metaphase 1 be different from metaphase 2? How will anaphase 1 be different from anaphase 2? What is meant by segregation? When does this happen? 5. Explain the sources of genetic variability that take place in meiosis: crossing over and independent assortment and the stages in which they occur. 6. What others sources of genetic variability exist NOT being part of meiosis? Explain 7. If an organism that reproduces sexually has a TOTAL OF EIGHT (8) chromosomes, and we know that organisms are mostly diploid (di = two) because of the presence of two sets of homologous chromosomes, then… How many sets of chromosomes will the cells have? ……… What is the number of chromosomes per set? ……… What is the haploid number (n)? ……. What is the diploid number (2n)?……… 8. Explain what No disjunction (no segregation) means. What happens normally to the cells where No disjunction occurs? 9. Some No disjunctions are, however, viable (the sex cells survive). Eventually, if by chance these abnormal sex cells participate in sexual reproduction, the future baby will end up with and abnormal number of chromosomes. In other words, one chromosome will be missed in the pair of homologous chromosomes, or there will be three chromosomes instead of two. What name do these abnormalities in the number of chromosomes receive? 10. Give an example of a viable (that can live) abnormal chromosome number in the cells 11. The study of abnormal males and females phenotypes in humans helped to understand that sex is, in mammals, determined by chromosomes. a) Give the name of the two abnormalities associated with sex chromosomes. b) How “abnormal” are these phenotypes compared to normal men and women? 12. Why is the frequency of No disjunction higher in men’s meiosis than in women? MCC Biological Principles Based on work by Dr. Jose Bava
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