Week 5 Homework Key
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 since black is dominant over albino, all the F1 animals would have had black fur.
+1 point
Second Cross: Since some of the F1 offspring are albino, that means that the black parent must have been heterozygous for fur color. So, the parents of the second cross were Bb x bb. The black parent would have produced gametes carrying either the B or the b allele, while the gametes of the white parent carried only the b allele. The white F1 offspring would have been genotype bb and the black F1 offspring were genotype Bb.
+1 point
2. In Drosophila, three autosomal genes have alleles with the following dominance patterns:
Gray body (G) is dominant over black (g)
Full wings (A) is dominant over vestigial wings (a)
Red eye (R) is dominant over sepia eye (r)
Two crosses were performed with the following results:
Parents: heterozygous red, full wings, crossed with sepia vestigial wings
Offspring:
131 red, full
120 sepia, vestigial
122 red, vestigial
127 sepia, full
Parents: heterozygous gray, full wings, crossed with black, vestigial wings
Offspring:
236 gray, full
253 black, vestigial
50 gray, vestigial
61 black, full
Are any of these three genes linked on the same chromosome? If so, what is the map distance
(recombination rate) between them?
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 since black is dominant over albino, all the F1 animals would have had black fur.
+1 point
Second Cross: Since some of the F1 offspring are albino, that means that the black parent must have been heterozygous for fur color. So, the parents of the second cross were Bb x bb. The black parent would have produced gametes carrying either the B or the b allele, while the gametes of the white parent carried only the b allele. The white F1 offspring would have been genotype bb and the black F1 offspring were genotype Bb.
+1 point
2. In Drosophila, three autosomal genes have alleles with the following dominance patterns:
Gray body (G) is dominant over black (g)
Full wings (A) is dominant over vestigial wings (a)
Red eye (R) is dominant over sepia eye (r)
Two crosses were performed with the following results:
Parents: heterozygous red, full wings, crossed with sepia vestigial wings
Offspring:
131 red, full
120 sepia, vestigial
122 red, vestigial
127 sepia, full
Parents: heterozygous gray, full wings, crossed with black, vestigial wings
Offspring:
236 gray, full
253 black, vestigial
50 gray, vestigial
61 black, full
Are any of these three genes linked on the same chromosome? If so, what is the map distance
(recombination rate) between them?