AP BIOLOGY

Detailed explanation-1: -Recessive alleles are only expressed when no dominant allele is present. In most sexually reproducing organisms, each individual has two alleles for each gene (one from each parent). This pair of alleles is called a genotype and determines the organism’s appearance, or phenotype.

Detailed explanation-2: -Alleles can be dominant or recessive. Dominant alleles mask the effects of recessive alleles, so a recessive trait is only expressed when an organism has two recessive alleles for a gene.

Detailed explanation-3: -A recessive allele does not produce a trait at all when only one copy is present. This contrasts to a dominant trait, which requires that only one of the two alleles be present to express the trait.

Detailed explanation-4: -Recessive alleles are only expressed if both of a person’s alleles are recessive. If a person has one dominant allele and one recessive, he is called a carrier. This is because he expresses the dominant trait, but “carries” the recessive trait. An example of this is albinism.

Detailed explanation-5: -An allele is considered dominant when it masks the expression of the recessive trait in a heterozygous genotype. When you are homozygous for a recessive allele, the phenotype expressed is the recessive trait. If you are heterozygous, one of each, the dominant trait is expressed.