Question

What kinds of evidence suggest that the diversity observed in MHC alleles is beneficial to the survival of an individual or a population?

Answer 1

Many natural populations are threatened not only by a dramatic reduction in total area of available habitat but also by increasing habitat fragmentation and degradation leading to declining population sizes and barriers to gene flow if exchange of individuals between subpopulations is restricted. Small populations often suffer from reduction of genetic diversity due to genetic drift and inbreeding effects. Negative effects such as increased rates of allelic loss, fixation of deleterious alleles and decreased average individual heterozygosity relative to the overall population were observed by both, theoretical and empirical studies. The loss of genetic variation can lead to short-term reduction of fitness components such as survival, reproductive output, growth rates and to impaired ability to adapt to long-term changes in the environment. An increasing number of studies indicates that host genetic diversity plays an important role in buffering populations against pathogens and widespread epidemics.