Question

Explain why an individual must be homozygous if he is exhibit a recessive trait?

Answer 1

You have two copies of every gene (sex chromosomes not included).

If you have one recessive gene and one dominant gene, the recessive trait won't be exhibited. The dominant trait will show. This is a heterozygous individual. Recessive means it won't be exhibited unless there is no alternative trait.

So, the only way to exhibit a recessive trait is to have both copies of the gene being recessive. I.e. the same recessive gene on both chromosomes. This way, there is no dominant gene to overshadow the recessive one. Two copies of the same gene = homozygous.