Question

An allele that is expressed in the phenotype only when it is in the homozygous state is called __________.

A) Recessive allele
B) Dominant allele
C) Co-dominant allele
D) Neutral allele

Answer 1

A recessive allele is expressed in the phenotype only in the homozygous state, meaning the individual has two copies of the recessive allele. Dominant alleles are expressed in both the homozygous dominant and heterozygous states.

Step-by-step explanation:

An allele that is expressed in the phenotype only when it is in the homozygous state is called a recessive allele. For a recessive trait to be observed in an individual's phenotype, the person must have two copies of this allele (homozygous recessive). In other words, the trait will not be displayed in a heterozygous state where one dominant allele is present. If both parents carry a recessive allele for a trait, their offspring have a 25% chance of displaying the recessive trait if they inherit the recessive allele from both parents. In contrast, dominant alleles are expressed even if only one copy is present, in either the homozygous dominant (AA) or heterozygous (Aa) state. Therefore the correct answer is A) Recessive allele.