Question

The genotype of offspring formed from Tt X tt will be________.
(a) TT and tt
(b) Tt and tt
(c) Only tt
(d) Only TT

Answer 1

Hint: Mendel does his first successful hybridization experiment on a garden pea plant from which he obtained three different types of alleles like homozygous dominant, homozygous recessive, and heterozygous dominant. Mendel also introduces a test cross to know the homozygous and heterozygous nature of the dominant trait.

Complete answer:
When cross takes place between Tt and tt two different types of alleles are form,
  Tt X tt = Tt, Tt, tt, and tt.
The genotypic ratio for this cross is 1:1 and the phenotypic ratio is 1:1, where Tt is heterozygous dominant and tt is heterozygous recessive. This type of cross is a test cross.

Additional Information: The test cross takes place between dominant and recessive alleles. In a test cross, I homozygous dominant alleles cross with homozygous recessive alleles whereas in test cross II take place between heterozygous dominant and homozygous recessive. Test cross takes place to obtain homozygous and heterozygous alleles of unknown genotype. In the case of homozygous dominant and homozygous recessive test cross result obtain is 100 percent heterozygous dominant, whereas when test cross takes place between heterozygous dominant and homozygous recessive result to obtain is 50 percent heterozygous dominant and 50 percent homozygous recessive.
A test cross is also a type of back cross, in the back cross, the hybrid which obtains from the hybridization experiment is crossed with one of its parents. To obtain the maximum number of traits multiple backcrosses take place. Back cross is useful to obtain disease resistance, pest resistance, and a high protein variety of crops.
So, the correct answer is Tt and tt.

Note: In the case of monohybrid test cross phenotypic and genotypic ratio is 1:1, in the case of dihybrid test cross phenotypic and genotypic ratio is 1:1:1:1, and in the case of the trihybrid cross the ratio obtain is 1:1:1:1:1:1:1:1. The ratio of cross increases with an increase in the number of characters.