Question

The recessive gene is one that expresses itself in
A. Heterozygous condition
B. Homozygous condition
C. ${F_2}$ generation
D. Y-linked inheritance

Answer 1

Hint: Presence of a dominant gene masks the effect or expression of the recessive allele and this gene can only be expressed when there is presence of recessive alleles in a gene.

Complete answer:
First of all, you should know what a recessive gene is. Recessive gene is that gene whose effects are masked in the presence of dominant gene as recessive gene is only expressed when there is presence of recessive alleles in a gene otherwise it's effect is masked.
According to Mendel's law of inheritance, the dominant gene is dominant as it can express itself completely due to which it suppresses other's traits. This recessive gene can only be expressed in homozygous condition and in heterozygous condition, there is presence of both dominant and recessive alleles but dominant alleles mask the effect of recessive alleles.
If we look at options now, option A is a Heterozygous condition. This option is incorrect as recessive genes cannot express themselves in heterozygous condition as the dominant gene will mask its effect. Therefore this option gets eliminated.
Moving to option B which is Homozygous condition. In a homozygous condition, recessive allele can express itself as there is no dominant allele to mask its effect. Therefore, this is the correct option.
Moving to option C which is ${F_2}$ generation. This option is also incorrect because recessive gene does not express itself in ${F_2}$ generation but it expresses itself in homozygous condition. Therefore, this option is incorrect and it gets eliminated.
Last option D is Y-linked inheritance. This option is also incorrect because the recessive gene does not express itself in Y-linked inheritance but it expresses itself in homozygous condition. Therefore, this option is incorrect and it gets eliminated.

Thus, the correct answer is option B which is Homozygous condition.

Note:
For a recessive gene to express, the condition should be homozygous as in heterozygous condition, there is presence of both dominant and recessive allele. Dominant allele masks the effect of recessive allele and therefore, the correct option is B as The recessive gene is one that expresses itself in homozygous condition.