Genetics: Feedforward loop for diversity

Abstract

DNA-sequence analysis suggests that genetic mutations arise at elevated rates in genomes harbouring high levels of heterozygosity — the state in which the two copies of a genetic region contain sequence differences.

Figure 1. Generating variation

This simplified schematic demonstrates the changes in diversity that arise in intercrosses of a diploid organism, which has two sets of chromosomes, one from each parent. In inbred organisms, most genetic regions are homozygous — they are identical on both chromosomes (completely homozygous chromosomes are depicted here for simplicity). When inbred plants self-fertilize, levels of homozygosity remain the same in offspring. But in the first generation of a cross between two inbred strains, the offspring have two different copies of each gene (heterozygosity). Further intercrossing of offspring leads to a decrease in levels of heterozygosity, because some regions become homozygous once again. Yang et al. report that levels of heterozygosity correlate with the rate at which genetic mutations arise.