Praxis Biology (5236) Practice Exam

Incomplete dominance is at work when the heterozygous state shows an intermediate trait between the two homozygous parents. Here, crossing true-breeding red flowers with true-breeding white flowers gives pink offspring in the first generation because neither allele fully dominates the other. In the next generation, crossing pink individuals with each other yields red, white, and pink plants in a 1:2:1 pattern, which reflects the three possible genotypes (RR, RW, WW) and the fact that the RW genotype produces the intermediate pink phenotype. This fits incomplete dominance well, whereas complete dominance would produce red in the F1 and largely red in the F2, codominance would usually show both parental traits expressed together rather than a blended pink, and polygenic inheritance would create a continuous spectrum rather than discrete red, pink, and white phenotypes.