| Diploid populations may have an advantage over haploid populations for adaptive evolution in having twice the number of genes and hence twice the total target size for beneficial mutations. Using experimental evolution studies to test this theory, isogenic haploid and diploid isolates of Saccharomyces cerevisiae were serially transferred for 300 and 500 generations in high pH and high salinity environments, respectively. After 300 generations in a high salinity environment, haploid and diploid populations had a higher fitness in the experimental environment relative to their progenitor populations. Upon genetic characterization of these populations, the haploid populations contained multiple, additive, beneficial mutations. The heterozygous diploid population had at least three mutations; two were dominant beneficial mutations and one was a recessive deleterious mutation. After 300 generations in a high pH environment, diploid populations showed a small increase in fitness, while haploid populations showed no increase in fitness in the experimental environment. |
