In these mice, transcription of the ‘H’ allele leads to a precursor mRNA which is occasionally spliced abnormally (Baker et al., 2004), causing the development of mutant mature Bub1b mRNA that is not translated; this reduces the cellular BUB1B protein levels (Baker et al., 2004), leading to male and female infertility. This evidence concerns the gene BUB1B and female infertility.