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PS02_solutions - 1a 1b 4 chromosomes 8 chromatids Random...

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1a) 1b) 1c) 1d) 4 chromosomes 8 chromatids Random order at metaphase plate 4 chromosomes 8 chromatids chromosomes are paired and joined at chiasmata 2 haploid cells resulting from meiosis I. Metaphase II, chromosomes align randomly at metaphase plate. 2 chromosomes/cell 4 chromatids/cell
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2. Butterflies are ZW ZZ and the female is heterogametic. Since males and females show different phenotypic ratios, it is probably sex linked ( W -linked). If it is very rare, then some males are carriers (i.e. it is recessive) but may never exhibit the phenotype. Females will occasionally exhibit it because they have a W chromosome. First assume Z-linked recessive. You could collect a black female and a WT male and cross them. This should give you progeny where all females are wild type but males will all be carriers. You could then back-cross the F1 males with the mother, and this should give you offspring where 50% of males are black and 50% of females are black. If the trait is W-linked, however, you would still not see any black males.
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