In rats, several independently assorting autosomal genes affect coat color. Gene
ID: 97055 • 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. b. Deduce the genotype and phenotype of each parent in the following table. Explain your answers. 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.Explanation / Answer
Presence of AB genes produce grey colour, A-bb produce yellow, aaB produces black and aabb produces cream color. When C gene is absent, albinos are formed.
a) Parents are true breeding. F1 are all grey.
The parental genotypes are AABB, CC and AABB, cc (albino 1). F1 are AABB, Cc. In F2, grey individuals are either AABB, CC or AABB, Cc. Albinos in F2 are AABB, cc.
The genotype of albino-2 should be aabb, cc. Since the parents are true breeding heterozygous combination is not possible.
Albino-1 has AABB, cc genotype and albino-2 has aabb, cc genotype.
b) In cross 1, the parental genotypes are AaBb, Cc and AaBb, Cc. Both parents are grey colored. This is because albinos and grey offsprings are produced in large numbers. In cross 2, the parental genotypes are aaBb, Cc and aaBb, Cc. Here, the parental phenotypes are black.
c) Cross between grey colored and yellow produces albino and cream. So, C gene must be in heterozygous state in both the parents. Cream color is also expressed. So, A and B genes are also in heterozygous state. So, parental genotypes are AaBb, Cc and AaBb, Cc. Cross between these can produce aabb, Cc (cream color) and any A, B with cc (albino).
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