Germ cells are specialized cells that undergo mitotic proliferation followed by meiosis and cellular differentiation to generate haploid gametes for sexual reproduction. We are investigating several aspects of germ line biology using the nematode, Caenorhabditis elegans and related nematodes. The C. elegans germ line is particularly amenable to these studies due to its unique structural organization, the molecular genetics of the system, and the high degree of conservation with genes and pathways in humans. We are currently investigating 1) how meiosis differs in males and females; 2) how unpaired sex chromosomes of the heterogametic sex repair double strand breaks and are hidden from the checkpoint machinery; and 3) how different checkpoint pathways interact to ensure the faithful transmission of the genome.