Recessive gene can only express in homozygous condition because homozygous condition shows similar trait such has TT ( Tall) and tt( dwarf)
Here tt is the recessive trait.
But in heterozygous condition it shows different trait such has Tt( Tall)

Recessive genes are genes that are typically masked or not expressed in the presence of their dominant counterparts. They can only be expressed when an individual has two copies of the recessive allele, also known as being homozygous for the recessive gene.

Here's a detailed explanation of why recessive genes can express only in homozygous conditions:

1. Homozygous and Heterozygous Conditions:
- Homozygous condition: Homozygosity refers to the condition where an individual has two identical alleles for a particular gene. In the case of a recessive gene, both alleles would be recessive. For example, if we consider a gene for eye color, the recessive allele could be for blue eyes. In a homozygous condition, an individual would have two copies of the recessive allele, resulting in blue eyes.
- Heterozygous condition: Heterozygosity refers to the condition where an individual has two different alleles for a particular gene. In the case of a recessive gene, one allele would be dominant, and the other would be recessive. For example, if we consider the same gene for eye color, the dominant allele could be for brown eyes. In a heterozygous condition, an individual would have one copy of the dominant allele and one copy of the recessive allele. However, since the dominant allele masks the expression of the recessive allele, the individual would have brown eyes instead of blue.

2. Expression of Recessive Genes:
- Recessive genes are only expressed or visible in the absence of their dominant counterparts.
- In a heterozygous condition, where one dominant and one recessive allele are present, the dominant allele will be expressed, and the recessive allele will remain hidden.
- It is only in a homozygous condition, where both alleles are recessive, that the recessive gene can be expressed because there is no dominant allele to mask its expression.
- This is why the correct answer to the question is option 'A' - recessive genes can express only in homozygous conditions.

In conclusion, recessive genes can only be expressed when an individual is homozygous for the recessive allele. In heterozygous conditions, the dominant allele masks the expression of the recessive allele.