Haploid selection in animals

Selection in the haploid phase is well known in plants, but it is often ignored in animals. Recent studies show that haploid selection acts on diploid loci in animals in several ways; for example, via gametic gene expression, genomic imprinting, X inactivation and selection on non-transcribed genomic regions in sperm. Although haploid selection probably affects only a small fraction of the genome, the number of loci involved might be several hundred or more. Haploid selection is expected to have important consequences at these loci for diverse phenomena, including antagonism between adaptation to either the diploid or the haploid phases, conflict between levels of selection and the evolution of sexually dimorphic recombination rates. The topic is ripe for development: refined data about which loci experience haploid selection would open the door to a variety of comparative approaches that could illuminate how diverse forms of selection mold patterns of genetic variation.