Which of the following describes an allele whose characteristic phenotype is masked by the
presence of a second, different allele?

Recessive allele

Explanation:

An allele is a variant form of a gene responsible for a particular trait in an organism. During his experiments, Gregor Mendel who was referred to as the FATHER OF GENETICS discovered that organisms receives two forms of a gene from their parents. Each allele is different from the one another, as they encode different traits of the same gene. For example, a gene that codes for the height trait in humans contains two alleles: 'T' for tallness and 't' for shortness.

Mendel, then stated in his LAW OF DOMINANCE, that one of the alleles is capable of masking the expression of the second allele in a gene. He called the allele that masks, DOMINANT allele while the allele that is masked, RECESSIVE allele. In other words, when two different alleles combine, only one trait (dominant allele) will be produced. The other trait encoded by the second allele (recessive) has been masked or covered up. For example, a genotype Tt will produce a tall individual because allele T is dominant over allele t, and has therefore masked its short expression.

thinking it would be d not too sure but i think it's right