Sperm tales

Abstract

In many creatures, as diverse as humans and flies, the male-specific Y chromosome has accumulated genes that are involved in that cardinal male-specific function, making sperm. Work in the 1970s showed that human males with deletions of the Y long arm were infertile, and since then the bright light of positional cloning has been shone into the murky and repeat-ridden world of Yq. Because of the lack of recombination, genetic mapping is impossible, and the candidate genes DAZ and RBMY have been isolated by mapping de novo deletions associated with infertility: they do not tell a simple story. Both are multicopy, and no cases of causative point mutations in infertile males have been found. Genotype–phenotype correlations are baffling: for DAZ, deletion of the entire gene cluster gives a phenotypic range from a complete lack of germ cells to one case of fatherhood. Heretics might even suggest that DAZ is a non-functional relic.