Question

Allele 'A' has relatively lower fitness than does allele 'a.' Nevertheless, this lower fitness allele acts dominantly to the more fit 'a' allele. You can see this because the fitness phenotype of AA and Aa are the same (and equal to 0.9). This means that the beneficial effects of the more fit allele will be masked in heterozygotes.

Answer 1

The subject discusses how a less fit dominant allele 'A' can mask the expression of a fitter recessive allele 'a' in both homozygous and heterozygous conditions, demonstrating genetic dominance does not always correlate with increased fitness.

Explanation;

The scenario you've described involves a dominant allele 'A' that masks the expression of a more fit recessive allele 'a', even though 'A' has a lower fitness level. Since both homozygous (AA) and heterozygous (Aa) individuals exhibit the same fitness phenotype (0.9), we can see that the dominant allele 'A' is expressed over the allele 'a'. This is an example of how genetic dominance does not necessarily align with the fitness or survival advantage often assumed for dominant traits. Indeed, recessive alleles may sometimes offer a fitness benefit but remain hidden in the phenotype of heterozygotes due to the presence of a dominating allele.

The Law of Dominance can explain why a less fitness beneficial dominant allele might still be prevalent in a population. Those who are heterozygous (Aa) do not express the recessive phenotype, instead showing the dominant trait, and thus carry the allele 'a' through generations. Fitness, determined by the environment, can fluctuate, which means that an allele's advantage or disadvantage might vary depending on external conditions. This complexity underscores the dynamic nature of evolutionary processes.