In the context of evolution by natural selection, does natural selection act directly on an organism's genotype or phenotype?

• A. Both genotype and phenotype equally and independently, because selection targets DNA and traits as separate units of evolution.
• B. Genotype, because selection directly changes allele frequencies by targeting specific DNA sequences regardless of their expressed traits.
• C. Neither genotype nor phenotype, because genetic drift is the only mechanism that changes allele frequencies over time.
• D. Phenotype, because selection favors individuals with traits that affect survival and reproduction in a given environment.

Answer: (D)

Verified step by step guidance

1. Understand the difference between genotype and phenotype: The genotype is the genetic makeup of an organism (its DNA sequence), while the phenotype is the observable traits or characteristics that result from the interaction of the genotype with the environment.
2. Recognize that natural selection acts on traits that influence an organism's survival and reproduction, which are expressed as phenotypes, not directly on the underlying DNA sequences.
3. Recall that although natural selection changes allele frequencies in a population over time, it does so indirectly by favoring phenotypes that confer a reproductive advantage, thereby increasing the frequency of the genotypes that produce those phenotypes.
4. Eliminate incorrect options by noting that natural selection does not act equally and independently on genotype and phenotype, nor does it act directly on genotype without regard to phenotype, and it is distinct from genetic drift, which is a separate evolutionary mechanism.
5. Conclude that natural selection acts on the phenotype because it is the traits expressed by the organism that affect its fitness in the environment, leading to differential survival and reproduction.