EVIDENCE FOR CO-DOMINANCE OF THE HOMOTHALLIC GENES, HM-ALPHA-HM-ALPHA AND HMA-HMA, IN SACCHAROMYCES YEASTS

Abstract

To investigate the dominance and recessiveness of the homothallism genes, HM.alpha./hm.alpha. and HMa/hma, for mating-type conversion, hybrids with various configurations of the homothallic genes were constructed by fusion of protoplasts prepared from haploid strains having identical mating types. Eight different combinations of the homothallic genes were tested for their function by observing the mating and sporulation abilities of the fusion products. With few exceptions, nonmating and sporogenous fusion products were obtained from the following combinations: .alpha.HO hm.alpha. HMa + .alpha. ho hm.alpha. hma, .alpha. HO hm.alpha. HMa + .alpha. ho HM.alpha. hma, .alpha. HO hm.alpha. HMa + .alpha. ho HM.alpha. HMa, a HO HM.alpha. hma + a ho hm.alpha. hma a HO HM.alpha. hma + a ho hm.alpha. HMa and a HO HM.alpha. hma + a ho HM.alpha. HMa. All the fusion products from the .alpha. HO hm.alpha. HMa + .alpha. ho hm.alpha. HMa and a HO HM.alpha. hma + a ho HM.alpha. hma combinations showed mating types identical to those of the respective haploid strains. These results clearly support the co-dominance of the HM.alpha./hm.alpha. and HMa/hma alleles and indicate that the hm.alpha. allele has the same function as the HMa allele and that the hma allele has the same function as the HM.alpha. allele.