Genetic Basis of Adaptation and Maladaptation via Balancing Selection

Abstract

Since human left Africa about 100 thousand years ago, they experienced numerous environmental as well as social transitions. During these transitions, their genome too experiences various forms of selective pressure and retained favorable advantageous alleles in their genome by either positive selection or balancing selection, while removing deleterious alleles through purifying selection. However, when an individual with certain advantageous genetic diversity is migrated to new contrasting environment or lifestyle, the advantageous genetic diversity becomes disadvantageous and finally causing maladaptation. Thus, understanding the role of evolution in adaptation and also in the regulation of population dynamics, is highly important for identifying naturally occurring advantageous or disease risk allele in contemporary populations. Recent advancements in high-throughput sequence technologies have made it easier for understanding the impact of evolutionary forces on the genetic make-up of human in different environmental and social conditions in a far better way. Statistical tests described in this review will enable reader to identify various signatures of balancing selection in different time scales in a more comprehensive way. Additionally, these tests will also help in identifying naturally occurring advantageous or disease risk alleles with applications in animal breeding, nature conservation and human medicine.

Keywords: balancing selection; diversity; evolution; frequency-dependent selection; heterozygote advantages; maladaptation; polymorphism; population genomics.