Question

A pea plant is heterozygous for a character and recessive homozygous for another character. Both these characters are located on different chromosomes . Another pea plant of the same species is heterozygous for both the characters. If these plants are crossed , what proportion of their offsprings will be heterozygous only for one character ?

A. 25%
B. 50%
C. 75%
D. 100%

Answer 1

When crossing a pea plant that is heterozygous for one character and homozygous recessive for another with a plant that is heterozygous for both characters, the proportion of offspring heterozygous for only one character is 50%.

Step-by-step explanation:

The question asks for the proportion of offspring that will be heterozygous for only one character when a pea plant that is heterozygous for one character and homozygous recessive for another is crossed with a pea plant that is heterozygous for both characters. Since the characters are on different chromosomes, we are looking at a dihybrid cross.

Let's denote the heterozygous character with A (dominant allele) and a (recessive allele), and the homozygous recessive character with B (dominant allele) and b (recessive allele). The first plant would have the genotype Aa bb, while the second plant would have the genotype Aa Bb.

Using a Punnett square, we can predict the genotypes of their offspring. The gametes from the first plant would be Ab and ab, and the gametes from the second plant would be AB, Ab, aB, and ab. When we cross these, we get the following genotypes: AABb, AAbb, AaBb (two ways), Aabb (two ways), aaBb, and aabb.

Hence, the offspring that are heterozygous for only one character would be AAbb, aaBb, and, since there are two ways each for AaBb and Aabb, we count them once. This gives us four possibilities out of the eight total combinations (AABB, AABb, AAbb, AaBB, AaBb, Aabb, aaBB, aaBb, aabb), resulting in 50% of the offspring being heterozygous for only one character.The correct answer to the question is 50%.