In rats, several independently assorting autosomal genes affect coat color. Gene
ID: 49475 • 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
Part a.
Genotype of albino-1 parent is …
Explanation:
Genotype of albino-2 parent is …
Explanation:
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
Part b.
Parental phenotypes
Parental genotypes
Cross 1
x
x
Explanation:
Part b.
Parental phenotypes
Parental genotypes
Cross 2
x
x
Explanation:
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.
Part c.
Cross is … x
Explanation:
Punnett Square
Fill the punnet sq
Thank you
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
Part a.
Genotype of albino-1 parent is …AABBcc
Explanation: The genotype of true breeding grey parents is, AABBCC and the genotype of albino 1 is AABBcc, which would result in all grey offpring in F1 generation and 1/4 aldino in F2 generation (in F2 generation, the C gene will be expressed in the ratio of 1 CC : 2 Cc : 1 cc).
Genotype of albino-2 parent is …AAbbcc
Explanation: Again, the genotype of true breeding grey parents is, AABBCC and the genotype of albino 2 is AAbbcc, which would result in all grey offpring in F1 generation and 3/16 yellow in F2 generation (in F2 generation, the C gene will be expressed in the ratio of 1 CC : 2 Cc : 1 cc).
ee
b.
Cross 1: If we exclude the albino mice, the given phenotypic ratios are approximately 9:3:3:1 ratio. To exhibit this ratio, the genotype of the parents must be heterozygous i.e. AaBb. In F2 generation, the C gene will be expressed in the ratio of 1 CC : 2 Cc : 1 cc.
Cross 2: Again if we exclude the albino, the phenotypic ratios are approximately in 3:1 ratio. To exhibit this ratio, the genotype of the parents must be aaBb and aabb, the genotype for C gene is Cc in both the parents.
c.
The cross would be between AaBbCc and AabbCc. If we take the C gene as separately, the normal to albino mice ratio would be 3:1. The The phenotypic ratio is 6 yellow: 6 greyblack: 2 cream: 2 black. The punnett square is given below.
AB
Ab
aB
ab
Ab
AABb
AAbb
AaBb
Aabb
ab
AaBb
Aabb
aaBb
aabb
Ab
AABb
AAbb
AaBb
Aabb
ab
AaBb
Aabb
aaBb
aabb
Part a.
Genotype of albino-1 parent is …AABBcc
Explanation: The genotype of true breeding grey parents is, AABBCC and the genotype of albino 1 is AABBcc, which would result in all grey offpring in F1 generation and 1/4 aldino in F2 generation (in F2 generation, the C gene will be expressed in the ratio of 1 CC : 2 Cc : 1 cc).
Genotype of albino-2 parent is …AAbbcc
Explanation: Again, the genotype of true breeding grey parents is, AABBCC and the genotype of albino 2 is AAbbcc, which would result in all grey offpring in F1 generation and 3/16 yellow in F2 generation (in F2 generation, the C gene will be expressed in the ratio of 1 CC : 2 Cc : 1 cc).
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