We're told that the four Andorian sexes roughly correspond to two male sexes and two female sexes, but that they aren't literally male or female.
As I understand the Andorian reproductive process, the thaan
each contribute a gamete containing 1/4 of the eventual child's genetic material, the shen
contributes the largest gamete, and egg, containing 1/2 of the eventual child's genetic material, and the zhen
contributes no genetic material, but carries the zygote/embryo/fetus to term.
I find this slightly confusing. Biologically speaking, "female" is defined as an organism (or a part of an organism, where an organism is hermaphroditic) that produces ova (eggs), which are in turn defined as the largest gametes produced by the species. By this definition, a shen
would be unequivocally female.
Further, "male", biologically speaking, is defined as an organism (or a part of an organism, where an organism is hermaphroditic) that produces smaller gametes than the ova of its species. By this definition, the thaan
would be unequivocally male.
The poor zhen is unaccounted for.
What I find confusing is the contention that a shen
is only roughly female, and that thaans
are only roughly male. It doesn't seem to add up, unless something radically different is going on with Andorian reproduction than we've been led to believe.