Which alleles are favored in direction selection?

In directional selection, one extreme phenotype is favored over all others, often as a response to changes in the environment or the needs of the population. This selection process leads to an increase in the frequency of alleles associated with this advantageous phenotype.

The correct choice highlights that directional selection specifically targets alleles linked to a particular extreme trait. This means that individuals exhibiting this trait are more likely to survive and reproduce, thereby passing on their alleles to the next generation. Over time, this selective pressure can shift the overall genetic makeup of the population in the direction of that favored phenotype.

The other options do not align with the concept of directional selection. For example, both dominant and recessive alleles being favored equally would imply a balanced selection without favoring one extreme phenotype. Meanwhile, alleles causing genetic diseases or neutral alleles without significant effects on fitness are generally not advantageous in terms of survival and reproduction, making them unlikely to be favored in a directional selection context.