Final answer:
The given example demonstrates codominance, where both alleles for the same characteristic are simultaneously expressed in the heterozygote. Individuals with the Hh genotype have higher levels of cholesterol due to the expression of both dominant and recessive alleles.
Step-by-step explanation:
The example given demonstrates codominance. In codominance, both alleles for the same characteristic are simultaneously expressed in the heterozygote. In this case, individuals with the genotype HH have healthy levels of cholesterol (dominant allele), those with Hh have higher levels of cholesterol (codominant alleles), and those with hh have dangerous levels that often lead to heart attacks during childhood (recessive allele). This means that individuals with the Hh genotype will have both the dominant and recessive traits expressed in their phenotype, resulting in higher levels of cholesterol.
The situation in which individuals with genotype Hh have higher levels of cholesterol than those with HH, but not as high as those with hh, is an example of incomplete dominance.
The example provided demonstrates incomplete dominance, not codominance or simple dominant-recessive inheritance. In incomplete dominance, individuals with a heterozygous genotype (Hh) express an intermediate phenotype between that of homozygous dominant (HH) and homozygous recessive (hh) individuals. In this case, those with Hh have higher levels of cholesterol than those with HH but do not reach the dangerous levels of cholesterol expressed by hh individuals. Unlike codominance, where both alleles are expressed equally, incomplete dominance results in a blended or intermediate expression of the trait. This contrasts with polygenic inheritance, where a trait is influenced by multiple genes rather than a single gene.