If an individual has a recessive phenotype for a particular trait, it can be concluded that

A. both parents also had a recessive phenotype for that trait.

B. only one parent had a recessive phenotype for that trait.

C. both parents were homozygous for the dominant gene for that trait.

D. each parent had at least one recessive gene for that trait.

E. none of the above

D. Each parent had at least one recessive gene for that trait.

Explanation:

Actually, the correct answer would be "Each parent had at least one recessive allele for that trait", but we can consider D to be correct.

Recessive phenotypes are only expressed when both copies of the gene are recessive alleles. If you have one recessive allele and one dominant allele, your phenotype will be dominant, same way as if you both alleles were dominant.

Each allele is inherited from one parent, so you have one parental allele, and one maternal allele. If your phenotype is recessive, it means you inherited a recessive allele from your mother and one from your father, so you can conclude that both parents had at least one copy of the recessive allele. What you can't say is that both parents had a recessive phenotype, because it could be that they had one dominant and one recessive allele, so they would be able to pass on the recessive allele to the next generation, but their phenotype would be dominant.