What term describes the probability that two alleles chosen at random from a population are different?

The term that describes the probability that two alleles chosen at random from a population are different is heterozygosity. Heterozygosity specifically refers to the presence of different alleles at a genetic locus on homologous chromosomes. When considering a population, calculating the heterozygosity gives an indication of genetic diversity and variability within that population, as a high level of heterozygosity implies that there are many different alleles present.

The concept is significant in evolutionary biology and conservation genetics, as it can affect the adaptability and survival of populations. In essence, a population with a high heterozygosity level is typically more resilient to environmental changes, as it has a greater variety of alleles that could potentially help it thrive under new conditions.