An interesting one this.
BBC News - Male pill: gene discovery may lead to contraceptive
"It may be possible to develop a new male contraceptive pill after researchers in Edinburgh identified a gene critical for the production of healthy sperm.
Experiments in mice found that the gene, Katnal1, was vital for the final stages of making sperm.
The authors of
a study in PLos Genetics said a drug which interrupts Katnal1 could be a reversible contraceptive."