How can you distinguish a male mouse from a female? - briefly
Inspect the ventral region: males display a visible scrotum and a noticeably longer anogenital distance, while females lack a scrotum and have a shorter distance between the anus and genital opening.
How can you distinguish a male mouse from a female? - in detail
Distinguishing the sex of a house mouse (Mus musculus) requires examination of external anatomy, reproductive organs, and, when necessary, internal assessment.
External characteristics provide the quickest clues for adult specimens. The most reliable indicator is the anogenital distance (AGD): the space between the anus and the genital papilla is markedly longer in males than in females. Measure this gap with fine calipers; a male typically shows an AGD of 4–6 mm, whereas a female’s measurement rarely exceeds 2 mm.
Secondary visual cues include the presence of a visible scrotum and testes in mature males. The scrotal sac appears as a small, pinkish bulge beneath the tail base, often containing palpable, firm masses. In contrast, females lack this structure and display a smooth ventral surface.
The genital papilla itself differs: males possess a small, rounded protrusion with a central opening for the urethra, while females have a flatter, less pronounced papilla that leads to the vaginal opening.
For juveniles or ambiguous cases, dissection offers definitive confirmation. After euthanasia, expose the perineal region. In males, the testes descend into the scrotum, and the epididymis is attached to the spermatic cords. Females present an ovarian pair and a uterine horn extending from the cervix.
When live identification is required without invasive methods, ultrasonography can visualize internal reproductive structures. Male mice exhibit testes and seminal vesicles; females show ovarian follicles and a uterine lumen.
In research settings, genetic markers (e.g., Sry gene PCR) provide a molecular approach, confirming sex with high accuracy regardless of developmental stage.
Summary of practical steps:
- Measure anogenital distance—longer in males.
- Inspect for scrotal sac and testes—present only in males.
- Observe genital papilla shape—rounded with central opening in males, flatter in females.
- If uncertainty remains, perform dissection, ultrasonography, or molecular assay.
These methods together enable precise sex determination across developmental stages and experimental contexts.