How can you distinguish a male mouse? - briefly
A male mouse can be identified by a visible external penis and a shorter anogenital distance than in females. The testes appear as a small, pale sac located behind the abdomen.
How can you distinguish a male mouse? - in detail
Distinguishing the sex of a mouse requires direct observation of external anatomy and, when necessary, supplementary methods.
The primary indicator is the presence of a scrotal sac. In adult males, the scrotum lies ventrally, just posterior to the penis, and contains palpable testes. The testes are visible as two oval masses within the sac, especially in light‑colored strains. Females lack a scrotum; instead, the perineal region shows a single opening (the vaginal orifice) situated closer to the anus.
Additional morphological cues include:
- Anogenital distance: The space between the anus and the genital opening is noticeably longer in males. Measuring this distance with calipers provides a reliable metric for juveniles before testes are fully developed.
- Body size: Males often exhibit modestly greater body mass and longer tails, though strain‑specific variation can limit usefulness.
- Nipple pattern: In many laboratory strains, females retain functional mammary glands with more pronounced nipples, while males have rudimentary or absent nipples. This trait becomes apparent after weaning.
- Scent glands: Males develop larger flank and preputial glands, producing a stronger odor that can be detected by trained personnel.
When visual assessment is ambiguous—such as in very young pups or in strains with reduced sexual dimorphism—genetic or molecular confirmation is advisable. Common approaches include:
- Polymerase chain reaction (PCR) targeting the Sry gene, the definitive male sex‑determining locus.
- Karyotyping to identify XY versus XX chromosome complements.
- Hormone assays measuring circulating testosterone levels, which are elevated in males after puberty.
For routine colony management, the combination of scrotal inspection and anogenital distance measurement yields rapid, accurate sex determination. Molecular confirmation should be reserved for research protocols requiring unequivocal sex verification.