Crossword-Solution: MMXX 4 letters, 2 clues 🏆 scrabble score: 22

Thus supposing _M_ to represent a modification acquired in the male and _m_ the absence of the modification, such as the feathered antenna of a moth, and the sex-chromosomes to be _X_ and _Y_, then we should have in the gametocytes-- Male Female _MM mm_ _XX XY_ Gametes _MX, MX: mXmY_ Zygotes _MmXX male, MmXY female_, and the character _M_ would only appear in the male because it only develops in association with _XX_ in the somatic cells descended from the male zygote.