 |  Biology, 6/e Author Dr. George B. Johnson,
Washington University
Author Dr. Peter H. Raven,
Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer,
Carleton College
Contributor Dr. Jonathan Losos,
Washington University
Sexual Reproduction and Meiosis
Answers to Review Questions|
Chapter 12 (p. 238)
1. Meiosis produces haploid gametes (egg or sperm). Syngamy produces a diploid zygote.
2. Meiosis is characterized by synapsis between homologous chromosomes and two divisions, one of which is a reduction division. Mitosis is characterized by one division and no reduction division.
3. Synaptonemal complexes hold homologous chromosome arms together, which facilitates crossing over. They are formed during prophase I.
4. Four chromatids are present. They are still held together at their common centromeres and at the synaptonemal complex.
5. Microtubules form the spindle but attach to only one face of each centromere at the kinetochore. The kinetochore of each homologue attaches to the pole toward its outer side, and the sides of the centromeres facing one another are not attached to a spindle fiber from either pole. In mitosis each centromere region attaches to spindle fibers from both poles. In meiosis, then, an entire chromosome is pulled to a pole in anaphase I, whereas in mitosis only a single chromatid is pulled to a pole.
6. The chromosomes move to the poles in a random fashion, and some paternal and some maternal chromosomes move to each pole without regard to the movement of all other chromosomes.
7. It developed as a means to repair double-strand damage to DNA.
8. Sexual reproduction increases genetic variability through crossing over, independent assortment, and random fertilization. Genetic variability provides the raw material for natural selection and thus, evolution.
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2002 McGraw-Hill Higher Education