Mutations are changes in a cell’s genomic DNA sequence. Types of mutation include insertion, deletion, translocation, inversion, and duplication. An insertion is the addition of a nucleotide somewhere in the DNA; a deletion is the opposite. A translocation mutation involves the physical movement of DNA segments, and can occur within a chromosome or between different chromosomes. Genetic drift, on the other hand, is a type of sampling error that leads to the perceived allele frequency changing among generations.

Horizontal gene transfer is a method of transferring genetic material from one organism to another and is common among bacteria. Horizontal gene transfer is an example of gene flow, a mechanism of evolution that involves the flow of genes among populations, species, and organisms. Natural selection involves uneven survival and evolutionary fitness due to the advantages granted to certain individuals through genetic variation. A mutation is an unplanned change in the DNA sequence of a cell or organism. Genetic drift is the change in an allele frequency in a population due to random sampling.

Stabilizing selection is a type of selection that decreases genetic diversity and stabilizes an optimum trait. In this situation, there is selection against extreme phenotypes. It is the opposite of disruptive selection and similar to purifying selection.

Directional selection is a type of natural selection in which one extreme phenotype is selectively advantageous. In other words, individuals with this trait are more likely to be reproductively successful. In this type of selection, one advantageous allele increases in frequency over time.

Disruptive selection is a type of natural selection in which the extremes of a phenotype are favored. This means that there is active selection against intermediates. It increases genetic diversity and is the opposite of stabilizing selection.

Positive selection is a type of natural selection in which the frequency of an allele increases.

Negative selection is a type of natural selection in which the frequency of an allele decreases.

Sexual selection is selection for traits that confer greater reproductive success. This includes selection for traits that better attract mates.

The heterozygote advantage is when a heterozygote phenotype increases fitness, as compared to both homozygote phenotypes. An example of this in human populations is sickle cell anemia—a condition where red blood cells cannot properly transport oxygen. Individuals that are heterozygotes are resistant to malaria. The example of sickle cell anemia demonstrates that heterozygosity may confer advantages and disadvantages, but homozygosity only confers a disadvantage.

Interference competition is a type of competition that occurs directly between individuals through the use of aggression.