Dominant alleles express the same phenotype regardless of zygosity

Steps:

• Recall that dominant alleles mask recessive ones in heterozygotes, determining phenotype expression.
• Evaluate each option against the definition of dominance.
• Eliminate A, B, and C as they misrepresent mutation, survival, or frequency unrelated to dominance.
• Confirm D matches the core principle of phenotypic uniformity.

Why D is correct:

• By definition, a dominant allele produces its full phenotype in both heterozygotes (where it masks the recessive) and homozygotes, ensuring the same observable trait.

Why the others are wrong:

• A: All alleles, including dominant, can mutate; dominance does not prevent genetic changes.
• B: Dominance affects phenotype, not inherent survival advantages, which depend on environmental selection.
• C: Allele frequencies vary by population dynamics, not dominance; dominant alleles can be common or rare.

Final answer: D