Sry does not fully sex-reverse female into male behavior towards pups

Investigations in mice suggest that the Y-chromosomal genes affect certain behaviors. Here, we studied whether a part of the Y chromosome, the Sxr locus, has an effect on induction of motivation for parental care (pup retrieval) or of parental aggression towards pups (infanticide). XX females, XX males with the Sxr locus on the X chromosome, and XY males of the C57BL/6J strain were tested. The induced pup retrieval or infanticide behaviors were genotype-dependent. XX mice always retrieved pups and never were infanticidal. On the first test, significantly more XY males (38%) than XX males (17%) were infanticidal. When the same animals were tested for a second time, all except one of the XX males retrieved pups. Overall, motivation for parental care was highest in XX females, followed by XX males, and lowest in XY mice. On the other hand, the incidence of infanticide was highest in XY males, lower in XX males, and absent in XX females. We conclude that the Sxr locus of the Y chromosome, when operating in a XX background, partially erases but does not fully defeminize motivation for pup retrieval. Further, it induces infanticide to a level higher than that of XX females but significantly lower than that of normal males (XY). Hence, we suggest that genes outside the sex-determining region of the Y chromosome and/or genes on autosomes are necessary for manifestation of full male-type parental behavior.