Question

In the \[{{F}_{2}}\] generation of a dihybrid cross between yellow, round seeded and green, wrinkled seeded pea plants, 17 out of 254 pea seeds were green and wrinkled. Other seeds were: Yellow and round; green and round; yellow and wrinkled. These results indicate which of the following statements?
A. Crossing over has occurred.
B. Green and wrinkled are both recessive characters.
C. The alleles for green and wrinkled are linked.
D. The allele for green is recessive but not the allele for wrinkled.

Answer 1

Hint: In order to solve this question we need to know that a dihybrid cross is a union of two individuals which have two features that may be observed and which are determined by two different genes. The recessive traits are present in lesser proportion in the cross.


Complete step by step solution:
Mendel crossed features that are in opposition to one another, like the colour and form of seeds, one at a time. He crossed the round, golden seed and the wrinkled, green seed. In the F1 generation, all he could find were spherical yellow seeds. This demonstrated that seeds are primarily spherical and yellow in colour in the natural world.
In contrast, the seeds' wrinkled shape and green colour are distinct characteristics. F1 offspring was later self-pollinated. Four distinct seed combinations were produced as a result for the F2 generation. Within the phenotypic ratio of 9:3:3:1, there were wrinkled-yellow, round-yellow, wrinkled-green, and round-green seeds.
He noticed the similar dominance and inheritance pattern during the monohybrid cross of these features. Hybridization also maintained the 3:1 phenotypic ratio of the round and wrinkled seed form and the colours yellow and green.
In dihybrid cross, we can see that the recessive traits are lesser in proportion for example here round seed and green wrinkled seeds are very less in proportion (17 out of 254) that means they are recessive in nature.
Hence, the correct option is B. Green and wrinkled are both recessive characters.


Note:
The thing to note here is that in case of dihybrid cross, there are two traits that are being studied together. The phenotypic ratio comes out to be 9:3:3:1, here the highest ratio would be of individuals with the dominant trait and least would be those with recessive traits.