S3 - S1.A diploid cell has eight chromosomes four per set...

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S1.A diploid cell has eight chromosomes, four per set. In the following diagram, what phase of mitosis, meiosis I or meiosis II, is this cell in? Answer: The cell is in metaphase of meiosis II. You can tell because the chromosomes are lined up along the metaphase plate, and it has only four pairs of sister chromatids. If it were mitosis, the cell would have eight pairs of sister chromatids. S2. An unaffected woman (i.e., without disease symptoms) who is heterozygous for the X-linked allele causing Duchenne muscular dystrophy has children with a normal man. What are the probabilities of the following combinations of offspring? A. An unaffected son B. An unaffected son or daughter C. A family of three children, all of whom are affected Answer: The first thing we must do is construct a Punnett square to determine the outcome of the cross. N represents the normal allele, n the recessive allele causing Duchenne muscular dystrophy. The mother is heterozygous and the father is hemizygous for the normal allele. A. There are four possible children, one of whom is an unaffected son. Therefore, the probability of an unaffected son is 1/4. B. Use the sum rule: 1/4 + 1/2 = 3/4. C. You could use the product rule, since there would be three offspring, in a row, with the disorder: (1/4)(1/4)(1/4) = 1/64 = 0.016 = 1.6%.

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S3. What are the major differences between prophase, metaphase, and anaphase when comparing mitosis, meiosis I, and meiosis II? Answer: The table summarizes key differences. A Comparison of Mitosis, Meiosis I, and Meiosis II Phase Event Mitosis Meiosis I Meiosis II Prophase Synapsis: No Yes No Prophase Crossing Rarely Commonly Rarely over: Metaphase Alignment Sister Bivalents Sister along the chro- chro- metaphase matids matids plate: Anaphase Separation Sister Bivalents Sister of: chro- chro- matids matids S4. Among different plant species, gametophytes can be produced by single individuals or by separate sexes. In some
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S3 - S1.A diploid cell has eight chromosomes four per set...

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