When two individuals who are heterozygous for a gene are mated, we would predict a _____ ratio of dominant to recessive phenotype in the offspring.
A)1:2:1
B)1:3
C)3:1
D)9:3:3:1

Question

Quizplus · Accepted Answer

When two individuals who are heterozygous for a gene (Aa x Aa) are mated, we predict a 3:1 ratio of dominant to recessive phenotype in the offspring. This is because there is a 25% chance of inheriting two recessive alleles (aa) and a 75% chance of inheriting at least one dominant allele (AA or Aa), which results in the dominant phenotype. This is known as Mendelian inheritance and follows the laws of segregation and independent assortment. Choice A (1:2:1) and choice B (1:3) are both ratios that occur in other types of genetic crosses, but not in a simple heterozygous cross like this one. Choice D (9:3:3:1) is the ratio for a dihybrid cross involving two different genes, not just one.

When Two Individuals Who Are Heterozygous for a Gene Are