Question

Dihybrid test cross ratio is
A. 9:9:3:1
B. 1:1:1:1
C. 3:1
D. 1:1.

Answer 1

Dihybrid id a cross between two genes that are different from each other in two observed traits. There are recessive and dominant alleles and the characters and traits of the offspring are dependent on these alleles.

Complete answer:
Dihybrid as the name itself means two alleles that have different traits and their cross will help in combining the genetic information. The crossing of the dihybrid F1 individual with homozygous recessive parents is called Dihybrid test cross. This is a test cross involving the individual which is homozygous dominant for both of the traits compared with the all recessive test cross individual. This test cross with the all recessive traits will determine the genotype based on the offspring ratio.
If the first parent is heterozygous for the both traits the ratio of the phenotypes looks different. There will be four possible outcomes in this test cross which will include one individual with both dominant alleles, one individual with first dominant and other recessive allele, one individual with first recessive and other dominant allele and one individual with both recessive alleles (RY, Ry, rY, and ry). After combining with single gametes produced by test cross parents we get RrYy, Rryy, rrYy, and rryy and the ratio will be 1:1:1:1. For example the colour and shape of pea seeds of pea, if wrinkled-green and round-yellow seeds are crossed. We will obtain only one round yellow seed in F1 generation. If this F1 generation is self-pollinated the result will be four different combinations of seed in F2 generation. They will be wrinkled-yellow, round-green, wrinkled-green, round-yellow.

Hence, the correct option is B. 1:1:1:1.

Note: The characters and traits acquired by the offspring depend on the characters in the parents and if those characters are dominant or recessive as dominant characters are generally shown by the offspring.