Sex-determining chromosomes and sexual dimorphism: insights from genetic mapping of sex expression in a natural hybrid Fragaria × ananassa subsp. cuneifolia

We studied the natural hybrid (Fragaria × ananassa subsp. cuneifolia) between two sexually dimorphic octoploid strawberry species (Fragaria virginiana and Fragaria chiloensis) to gain insight into the dynamics of sex chromosomes and the genesis of sexual dimorphism. Male sterility is dominant in both the parental species and thus will be inherited maternally, but the chromosome that houses the sex-determining region differs. Thus, we asked whether (1) the cytotypic composition of hybrid populations represents one or both maternal species, (2) the sex-determining chromosome of the hybrid reflects the location of male sterility within the maternal donor species and (3) crosses from the hybrid species show less sexual dimorphism than the parental species. We found that F. × ananassa subsp. cuneifolia populations consisted of both parental cytotypes but one predominated within each population. Genetic linkage mapping of two crosses showed dominance of male sterility similar to the parental ...