Chlamydomonas reinhardi: heterozygous diploid strains.

Zygotes of the unicellular green alga Chlamydomonas reinhardi occasionally divide mitotically to give rise to stable diploid vegetative strains. As well as by their mode of origin, these strains are distinguished from haploids by cell and nuclear size, DNA content per nucleus, and chromosome number. Diploid strains heterozygous for a variety of mutant genes are phenotypically wild type and mating-type minus. Thus these mutant genes are recessive to their wild-type alleles, and the mating-type-minus is dominant over the mating-type-plus allele.