Final answer:
Heterozygosity is quantified using a test cross or the Hardy-Weinberg principle, where an organism expressing a dominant trait is crossed with a homozygous recessive organism, or genotype frequencies are calculated based on allele frequencies.
Step-by-step explanation:
Heterozygosity can be quantified through a process known as a test cross, which was developed by Gregor Mendel. This technique involves crossing an organism that displays a dominant trait with one that is homozygous recessive for the same trait.
If the organism with the dominant trait is a homozygote, all the F1 offspring will be heterozygotes expressing the dominant trait. However, if the organism is a heterozygote, there will be a 1:1 ratio of heterozygotes to recessive homozygotes among the F1 offspring.
Additionally, using the Hardy-Weinberg principle, with given allele frequencies (p and q), where p + q = 1, the genotype frequency can be calculated using p² for homozygous dominant genotype (AA), 2pq for heterozygous genotype (Aa), and q² for homozygous recessive genotype (aa), ensuring that all genotype frequencies add up to 1.