In rats, several independently assorting autosomal genes affect coat color. Gene
ID: 49481 • Letter: I
Question
In rats, several independently assorting autosomal genes affect coat color. Gene A controls the distribution of yellow pigment in hair, and gene B causes black pigmentation. The two genes interact as follows: A–B– (gray), A–bb (yellow), aaB– (black), and aabb (cream). These genotypes are only expressed in the presence of the dominant allele of a third gene, C; rats with genotype cc are albino.
a. Deduce the genotype of each albino mice, to the extent that is possible, in the following table. Explain your answers.
True-breeding parents
F1
F2 offspring
Gray x albino-1
All gray
3/4 gray : 1/4 albino
Gray x albino-2
All gray
9/16 gray : 3/16 yellow : 4/16 albino
b. Deduce the genotype and phenotype of each parent in the following table. Explain your answers.
Parents
Numbers of offspring
Cross 1
135 gray, 83 albino, 47 yellow, 44 black, 16 cream
Cross 2
103 albino, 74 black, 25 cream
c. A gray-colored rat is mated with one that is yellow. The offspring include an albino rat and a cream-colored rat. Diagram this cross. Be sure to include the Punnett square and the phenotypic ratio in the offspring.
True-breeding parents
F1
F2 offspring
Gray x albino-1
All gray
3/4 gray : 1/4 albino
Gray x albino-2
All gray
9/16 gray : 3/16 yellow : 4/16 albino
Explanation / Answer
a.
The parental albino of the 1st cross is AABBcc.
Since the gray parent has AABBCC, the F1 progeny is fully gray. In the F2, the cc genotype comes out.
The ratio of the C gene in the F2 is 1 CC : 2 Cc : 1 cc.
Hence, we see the 1/4 albino progeny in F2.
In the second cross, the albino parent is AaBbcc. This would be the reason for the different colors seen in the F2 progeny.
b.
If you ignore the albino, you see the 9:3:3:1 ratio in the offspring. Regarding the albino genes, the ratio of the C gene in the F2 is 1 CC : 2 Cc : 1 cc. The parents should be heterozygous for the other 2 genes to get the 9:3:3:1 ratio. The genotype would be AaBb and AaBb.
In the second cross, the parents should be Cc for the albino gene. If we ignore the albino, we see a 3:1 ratio in the progeny. For this, both parents should be aaBb and aabb.
c.
To get a cream and an albino progeny the genotypes of the parents should be AaBbCc and AabbCc. Taking the C gene separately, we see a 3:1 ratio of normal: albino. For the other 2 genes, the punnet square is:
The phenotypic ratio would be: 6 grays: 6 yellow : 2 black: 2 cream
AB Ab aB ab Ab AABb AAbb AaBb Aabb ab AaBb Aabb aaBb aabb Ab AABb AAbb AaBb Aabb ab AaBb Aabb aaBb aabbRelated Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.