Sex, side, and severity in spontaneous malformations of fetal A/JKt mice, and their associations with each other and with fetal weight.

Cleft lip and palate (CLP) and open eyelid (OL) occur spontaneously in rather high frequencies in A/JKt mice, but vary greatly in their degree, laterality, and sex distribution. CLP occurs significantly more often in females, and OL even more often in males, than in the opposite sex. The female preponderence for CLP was largely if not entirely due to the increased rate of occurrence of left and incomplete forms of the defect, and to the excess in females heavier than the female median weight; whereas the male preponderance for OL could not be explained by any clear or major disparities of these sorts. CLP and OL occurred together more often than expected in individuals, but not in litters. There was no relation between the rate of defects in successive litters of the same female; nor was a relation detected between extent and severity of defect.