FETAL H-2 ODORTYPES ARE EVIDENT IN THE URINE OF PREGNANT FEMALE MICE

The major histocompatibility complex (MHC) imparts to each mouse an in dividual urinary odor, called ''odortype'', which reflects its MHC gen otype. Perception of odortypes affects mate selection and embryonic im plantation. Recent findings that odortypes are expressed as early as o ne day of age suggested that they might already be expressed in utero. We now report that at 9-12 days of gestation, odortypes specified by paternal (non-maternal) MHC haplotypes become apparent in maternal uri ne. Thus, odortypes are expressed in utero, can be sensed even before birth, and may serve in familial identification and communication.