The genes for the color of the cat’s coat are located on the X chromosome. Black color is determined by the B gene, red – by the b gene, heterozygotes have a tortoiseshell color. From a black cat and a ginger cat were born: one tortie and one black kitten. Make a scheme for solving the problem. Determine the genotypes of the parents and offspring, the possible sex of the kittens.
Let’s designate the gene that determines the development of red hair in kittens as b, then the chromosome in the structure of which this gene is inherited by descendants, we will designate as X b.
Let’s designate the gene that determines the development of black hair in kittens as B, then the chromosome with this gene in the structures will be designated X B.
Since the male sex is heterogametic in felines, individuals with spotted, tortoiseshell coat color will necessarily be female representatives with a heterozygous genotype X B X b.
A cat with black hair has a homozygous genotype X B X B and produces the same type of eggs – X B.
A cat with red hair has the genotype X b Y and produces sperm cells X b and Y.
The offspring of such cats and cats will include the following two possible options:
female kittens with tortoiseshell hair (X B X b) – 50%;
male kittens with black hair (X B Y) – 50%.
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