Final answer:
To test Hardy-Weinberg equilibrium assumptions, phenotypes must be observable and quantifiable. This allows researchers to compare observed phenotype frequencies with expected genotype proportions and evaluate if a population aligns with HWE.
Step-by-step explanation:
In Hardy-Weinberg equilibrium (HWE) testing, phenotypes must be observable and quantifiable. This allows for the comparison of observed frequencies of phenotypes with expected frequencies based on genotype proportions. To assess whether a population is in HWE, it is necessary to count individuals according to their expressed traits (phenotypes) and to adjust these counts to a Mendelian expected ratio if simple Mendelian inheritance is assumed.
Mendel's hybridization experiments provide a clear example of the difference between phenotype and genotype. For instance, when true-breeding yellow pod plants were crossed with green pod plants, the F1 generation showed only yellow pods, displaying the dominant phenotype. However, since the green phenotype reappeared in the F2 generation, it indicated that the F1 hybrids had a different genotype carrying both the dominant and recessive alleles. This type of analysis is critical when applying HWE, which assumes no change in allele frequencies over time, and is used to understand the genetic structure of populations.