Week 5 Homework Key

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Week 5 – Homework – Answer Key
Due Feb. 23, 2013
A total of 20 points are possible for this homework
1. A black guinea pig is crossed with an albino guinea pig, producing 12 black offspring. When the very same albino is crossed with another black guinea pig, 7 black and 5 albinos are obtained. Explain this genetic outcome by writing out the genotypes for the parents, gametes, and offspring in both crosses.
First Cross: The fact that all F1 offspring are black suggests that the parents of the first cross were genotype BB x bb (where B=black and b=albino). The gametes produced by the black parent would have carried the B allele, while those produced by the albino parent carried the b allele. The F1 offspring of such a cross would be Bb, and
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Tan could also be autosomal dominant. Under these circumstances the tan female parent would be heterozygous (Tt) and the wt male would be homozygous recessive (tt). A cross between these two would still produce 50:50 normal colored / tan offspring, of both sexes.

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A Third solution: tan and curved are both sex linked.
C = wt wings, c = curved wings (recessive)
T = tan body, t = wt body color (recessive)

XcT / Xct

Female Parent fly is
Male P fly is

This works, too!
+2 points for any workable solution

4. Clear wing, Black eye, and Hairless (c, b, and h) are linked, recessive traits carried on chromosome 3 of the Narragansett quahaug fly. A clear-winged, black-eyed fly is crossed with a hairless fly.
A) Their F1 offspring were 97 wild type quahaug flies. What is the genotype of these F1 flies??
[4 points]

Cc Bb Hh

or, [cbH / CBh], etc…
(heterozygous for all 3 traits)
+2 points for genotype

10 of these flies were then mated with flies that exhibit all three traits (clear-winged, black-eyed, and hairless). They produced a total of 1,000 F2 offspring: clear-wings, black eyes hairless clear wings black eyes, hairless wild type clear wings, black eyes, hairless black eyes clear wings, hairless

CB cbh CbH cBh 415

• Use these data to construct a map of these three genes in two steps.
• Use these data to construct a map of these three genes, showing your work along the way. The map should show the order of the

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