Two black female mice are crossed with a brown male. One female in several litters gave

Two black female mice are crossed with a brown male. One female in several litters gave: 7 brown, 9 black, the second – 17 black mice. What conclusions can be drawn regarding the color of inheritance black and brown? What are the genotypes of the parents?

In the second cross, all mice born to a black female mouse and a brown male have black hair. It should be concluded that the brown hair gene is recessive in mice. Let’s designate it as p, then the gene that determines the development of black wool will be P.

A male with brown hair will be homozygous for the recessive trait gene – pp, which is a prerequisite for the phenotypic realization of traits from the recessive category. This male is capable of producing only one type of sperm – p.

Consequently, all black mice born by the second female are heterozygous – PP, and the female herself is homozygous for the dominant gene of black wool – PP, producing and transmitting to the offspring only eggs with the gene of black wool P.

In the first cross, phenotype splitting is observed in the offspring. Brown mice, like the male, have the pp genotype, therefore, the black females from the first crossing are heterozygous – pp. They produce two types of oocytes – P and p. When crossed with a brown male, the following offspring options are produced: 50% pp – brown mice, 50% pp – black mice.

The resulting percentage corresponds to the 1: 1 ratio, characteristic of the analyzing crossing of heterozygotes with homozygotes for the recessive gene, and also corresponds to the actually obtained numerical values ​​from the condition of the problem (7: 9).

Answer: the gene for the black coat of mice dominates over the gene for the brown coat; the brown male is homozygous for the recessive gene (cc), the first black female is heterozygous (Cc), the second black female is homozygous for the dominant gene (CC).