How can you distinguish mice by sex? - briefly
Sex is identified by inspecting the anogenital distance and external genitalia; males display a longer distance and visible testes, whereas females have a shorter distance and a vaginal opening. Additional indicators include nipples present in females and the shape of the perineal region.
How can you distinguish mice by sex? - in detail
Sex identification in mice underpins experimental validity and colony management. Reliable determination relies on a combination of external examination, internal assessment, and molecular analysis.
External characteristics provide the quickest assessment. Typical indicators include:
- Anogenital distance (AGD): Males exhibit a markedly longer AGD than females, measurable with calipers from the anus to the genital papilla.
- Genital morphology: Males possess a prominent preputial sheath and a recessed scrotum; females display a smooth perineal region with a visible vaginal opening.
- Nipple development: Adult females develop prominent mammary buds; males retain rudimentary or absent nipples, especially in the dorsal line.
External cues emerge at specific developmental stages. In neonates (post‑natal day 7–10), AGD differences become measurable, while genital morphology differentiates reliably by day 14. Adult mice present fully developed traits, allowing rapid visual discrimination.
When external features are ambiguous—such as in genetically modified strains with altered secondary sexual characteristics—internal examination offers confirmation. Dissection reveals gonadal morphology: testes are ovoid, encapsulated, and located within the abdominal cavity; ovaries consist of follicular structures with distinct cortical layers. This approach requires euthanasia and sterile technique.
Molecular methods eliminate reliance on phenotypic variation. Polymerase chain reaction targeting the Sry gene on the Y chromosome confirms male status. Sample collection involves a small tail snip or ear punch, followed by DNA extraction and amplification. Real‑time PCR provides rapid, quantitative results, suitable for high‑throughput screening.
Best practices integrate multiple modalities: initial visual inspection for routine colonies, supplemented by molecular verification for critical experiments or atypical phenotypes. Documentation of sex at the time of weaning, along with periodic re‑assessment, ensures consistency throughout the study lifecycle.