Question

Test cross ratio of 1:1:1:1 proves that-
a. F1 hybrid produces four different gametes.
b. F1 hybrid is homozygous
c. Two different progenies are produced by P1 parents.
d. None of the above.

Answer 1

Hint: Here we will explain with the help of Mendel’s law of independent assortment. But before that we should know that a test cross is defined as the process of cross breeding an individual with a phenotypically recessive individual to determine the zygosity.

Complete answer:
> Mendel’s law of independent assortment states that the inheritance pattern of one pair of factors or genes are independent of the inheritance pattern of the other pair of genes and all possible combinations may appear side by side. In other words, the genes don’t influence each other in relation to sorting alleles into gametes.

> Mendelian law of independent assortment explains that the alleles of two different genes get sorted into gametes independently from one another, without affecting each other. So, the test cross ratio shows that the F1 hybrid produced as a result of test cross consists of all four different species.

> The test cross ratio 1:1:1:1 proves that the F1 hybrid produces four different types of gametes, each one of which is expressed without affecting the other. The four different types of gametes appear side by side.

Hence, option a) F1 hybrid produces four different gametes, is correct.

Additional information:
The phenotypic ratio or classic Mendelian ratio for a test cross is 1:1:1:1. Here, the alleles of the two genes assort independently of each other into gametes. The result of this cross produces four different gametes and each one is different from the other. The test cross is hence, a test done to investigate the genotype of parents.

Note: The back cross and test cross are different. The test cross is used to differentiate and determine the genotype of the parents whereas, the back cross is used to recover the particular genotype from a parent which bears a particular genotype.