How can you differentiate the gender of mice? - briefly
Male mice are identified by a longer anogenital distance and visible testes within a scrotum; females have a shorter distance and no scrotal bulge. Palpation of the abdomen can confirm the presence of ovaries in females and the absence of testes in males.
How can you differentiate the gender of mice? - in detail
Determining the sex of laboratory mice requires a combination of external examination, molecular testing, and, when necessary, behavioral observation.
External assessment is the first step and works reliably after the first week of life. The key features are:
- Anogenital distance (AGD): Males exhibit a longer space between the anus and the genital papilla than females. Measure with calipers; a difference of 1–2 mm is typical in pups aged 10–14 days.
- Genital morphology: In males, the preputial opening is present, and the testes are visible under the skin after 21 days. Females lack a preputial fold and have a simple vaginal opening.
- Nipple count: Females possess five pairs of abdominal nipples, while males have only four pairs; the sixth pair is absent or rudimentary. Examination should be performed on gently restrained, warmed animals to enhance visibility.
When visual cues are ambiguous—such as in neonates before the development of secondary sexual characteristics—molecular techniques provide definitive identification:
- Polymerase Chain Reaction (PCR) for the Sry gene: Extract DNA from a small tail or ear punch, amplify the male‑specific Sry region, and run agarose gel electrophoresis. Presence of the Sry band confirms a male; absence indicates a female.
- Quantitative PCR (qPCR) targeting sex‑linked markers: Allows rapid high‑throughput screening with minimal tissue input.
Hormonal assays can supplement genetic data, especially in studies where endocrine status is relevant:
- Serum testosterone measurement: Elevated levels in males become detectable after puberty.
- Estradiol profiling: Higher concentrations in females, though overlap exists during certain developmental windows.
Behavioral indicators, while less reliable for early identification, can aid confirmation in adult groups:
- Territorial marking: Males frequently scent‑mark with urine.
- Maternal behavior: Females exhibit nesting and pup‑caring activities.
Imaging methods, such as high‑resolution ultrasound or micro‑CT, are employed in specialized contexts (e.g., when non‑invasive longitudinal monitoring is required). These modalities visualize internal reproductive structures—testes in males, uterine horns in females—without sacrificing the animal.
A practical workflow for routine colony management:
- Perform visual inspection at weaning (21 days). Record AGD, genital opening, and nipple pattern.
- For any ambiguous cases, collect a tissue sample for Sry PCR.
- Validate results with a secondary method (qPCR or hormonal assay) if the study demands high certainty.
Applying these procedures yields accurate sex determination across developmental stages, supporting experimental reproducibility and animal welfare.