How can you determine if a mouse is male or female? - briefly
Inspect the genital area: males display a protruding penis and a greater anogenital distance, whereas females have a recessed vulvar opening without a penis.
How can you determine if a mouse is male or female? - in detail
Determining the sex of a laboratory mouse requires direct observation or molecular analysis, depending on the animal’s age and the precision needed.
In neonates (up to 10 days old) the most reliable visual cue is the anogenital distance (AGD). Males exhibit a longer gap between the anus and the genital papilla than females. By gently spreading the hindquarters, the examiner can measure this distance with a caliper; a difference of 1–2 mm typically distinguishes the sexes. The presence of a small, rounded preputial gland in males and a smoother perineal region in females further confirms the identification.
In weanlings and adult mice, external genitalia become more distinct. Males possess a visible scrotum and larger testes that can be felt through the abdominal wall. Females lack a scrotum and display a simple vaginal opening without surrounding swelling. Additionally, adult females have a pair of functional nipples on each side of the thorax, whereas males have only a single pair of rudimentary nipples.
When visual assessment is impractical—such as with blind or severely furred strains—or when genetic confirmation is required, polymerase chain reaction (PCR) targeting sex‑specific markers provides definitive results. The Sry gene on the Y chromosome serves as a male‑specific target; amplification of this fragment indicates a male, while its absence denotes a female. An alternative is the amelogenin gene, which yields different fragment sizes for X and Y chromosomes, allowing simultaneous detection of both sexes in a single reaction.
Hormonal assays can supplement other methods. Elevated serum testosterone levels correlate with male physiology, whereas estradiol predominates in females. However, hormone concentrations fluctuate with the estrous cycle, making this approach less reliable as a sole diagnostic tool.
Ultrasound imaging offers a non‑invasive option for live animals. High‑frequency transducers can visualize the testes in males and the uterus in females, though operator skill and equipment cost limit routine use.
A practical workflow for sex determination might follow these steps:
- Neonatal stage – measure AGD and inspect the perineal region.
- Weanling/adult stage – palpate testes, examine scrotal development, and note nipple pattern.
- Molecular confirmation – perform PCR for Sry or amelogenin if visual signs are ambiguous.
- Supplementary checks – consider hormone assays or ultrasound when required by experimental design.
Accurate sex identification supports reproducible research outcomes and complies with ethical standards for animal handling.