Question

When a preexisting allele is changed to a new version that no longer codes for a functional protein, the new allele is called a ______ allele?

1) Dominant
2) Recessive
3) Neutral
4) Homozygous

Answer 1

The new version of an allele that no longer codes for a functional protein and can lead to a non-viable phenotype when in a homozygous state is called a recessive allele. Option number 3 is correct.

Step-by-step explanation:

When a preexisting allele is changed to a new version that no longer codes for a functional protein, the new allele is called a recessive allele. This term is used because the allele can only express its phenotype when present in both copies of a gene, meaning the individual must be homozygous recessive. These nonfunctional alleles usually do not affect the organism's phenotype when paired with a functional wild-type allele since the wild-type allele is dominant and hence masks the effect of the nonfunctional recessive allele.

For an essential gene, the inheritance pattern might be referred to as recessive lethal if carrying two copies of the nonfunctional allele leads to death, preventing the individual from developing past fertilization or surviving into adulthood. Therefore, the inheritance pattern distorts the expected genotypic ratio among surviving offspring to a 2:1, assuming that one quarter of the offspring that are homozygous for the recessive allele do indeed die.