How can I determine the sex of a wild mouse? - briefly
Examine the ventral region: males display a longer anogenital distance with a visible scrotum or testes, whereas females have a shorter distance and a naked genital papilla. If external characteristics are unclear, a brief dissection or ultrasound can provide definitive identification.
How can I determine the sex of a wild mouse? - in detail
Identifying the sex of a captured wild mouse requires careful observation and, when necessary, laboratory confirmation.
External morphology provides the quickest clues. In adult rodents, the anogenital distance (AGD) is markedly longer in males than in females. Males display a visible scrotum and a small, rounded penis positioned between the anus and the ventral surface. Females lack a scrotum; the genital opening is closer to the anus and the area appears smoother. In juveniles, sex can be inferred from the presence or absence of nipples: females develop multiple pairs along the ventral line, while males retain only a single pair near the thorax.
When visual assessment is ambiguous—particularly in young or poorly preserved specimens—palpation can help. Gently compress the lower abdomen to feel for testes in males; the testes are firm, oval, and situated laterally. Females will present a softer, uniform abdomen without distinct masses.
If external and tactile methods fail, dissection offers definitive results. After euthanasia, open the abdominal cavity and locate the gonads. Testes are paired, reddish‑brown, and attached to the epididymis. Ovaries appear as small, pale, almond‑shaped structures with surrounding fat.
Molecular techniques provide sex determination without reliance on physical traits. Collect a small tissue sample (ear punch, tail tip, or buccal swab) and extract DNA. Perform polymerase chain reaction (PCR) targeting sex‑specific genes such as Sry (male‑specific) and Xist (female‑specific). Gel electrophoresis reveals the presence or absence of the male marker, confirming sex even in neonates.
Practical considerations:
- Use a magnifying lens or stereomicroscope for accurate visual inspection.
- Handle mice with gloves to avoid stress and potential injury.
- Record the animal’s age class, as juvenile morphology differs from adult.
- Store tissue samples in ethanol or a suitable buffer if molecular analysis is planned.
- Follow ethical guidelines for euthanasia and tissue collection.
Combining external examination, palpation, dissection, and PCR ensures reliable sex identification across all life stages of wild mice.