Answer:
D. All of the above
Step-by-step explanation:
Allele is any of several forms of a gene, usually arising through mutation, that are responsible for hereditary variation.
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis, or meiosis or other types of damage to DNA, which then may undergo error-prone repair, cause an error during other forms of repair, or cause an error during replication.
Genetic drift is random changes in the frequency of alleles in a gene pool, usually of small populations.
Natural selection is the process by which lifeforms of life having traits that better enable them to adapt to specific environmental pressures, as predators, changes in climate, or competition for food or mates, will tend to survive and reproduce in greater numbers than other of their kind, thus ensuring the perpetuation of those favorable traits in succeeding generations.
In population genetics, directional selection, is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. Under directional selection, the advantageous allele increases as a consequence of differences in survival and reproduction among different phenotypes.
Positive selection keeps variants that are beneficial in specific environments, while negative selection removes genetic changes that are detrimental, for example because they cause disease.