A gene has two alleles B and b. B is responsible for the expression of character x. b is responsible for the expression of character y. B is completely dominant over b. Another gene A is epistatic on gene B. When A is in the dominant condition it suppresses the expression of B and b and gives rise to character z. In recessive condition (allele a) allows expression of B and b. When an organism with genotype AaBb is crossed with another organism with genotype AbBb, the ratio of characters x, y and z seen in its offsprings is

Question

A gene has two alleles B and b. B is responsible for the expression of character x. b is responsible for the expression of character y. B is completely dominant over b. Another gene A is epistatic on gene B. When A is in the dominant condition it suppresses the expression of B and b and gives rise to character z. In recessive condition (allele a) allows expression of B and b. When an organism with genotype AaBb is crossed with another organism with genotype AbBb, the ratio of characters x, y and z seen in its offsprings is, 3 : 4 : 9, 3 : 1 : 12, 1 : 12 : 3, 9 : 4 : 3

MARKS App · Accepted Answer

According to the data given, Character x will be expressed in organisms having genotypes aaBB or aaBb. Character y will be expressed in organisms having genotypes aabb. Character z will be expressed in organisms having genotypes A A B B , A A B b , A A b b , A a B B , A a B b and A a b b The cross A a B b x A a B b will produce, A A B B , A A b b , a a B B , a a b b , A a B B ( 2 ) , A A B b ( 2 ) , A a b b ( 2 ) , a a b ( 2 ) and AaBb (4). Thus, Character x will be expressed in a a B B ( 1 ) a n d a a B b ( 2 ) that is 3 out of 16 possibilities Thus, Character y will be expressed in a a b b ( 1 ) that is 1 out of 16 possibilities Thus, Character z will be expressed in A A B B ( 1 ) , A A B b ( 2 ) , A A b b ( 1 ) , A a B B ( 2 ) , A a B b ( 4 ) a n d A a b b ( 2 ) that is 12 out of 16 possibilities The ratio of x : y : z = 3 : 1 : 12

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