Describes how apospory can be used to produce genetically marked polyploid sporophytes, whose gametophyte progeny are heterozygous for mutations affecting sex determination in the gametophyte. Other feature of the gametophyte progeny; What segregation ratios of wild-type to mutant phenotypes in the gametophyte progeny of polyploid sporophyte plants indicate; Finding concerning the DNA content of the sperm of the progeny gametophytes.