How can the gender of mice be checked? - briefly
Inspect the anogenital area: males display a visible scrotum and enlarged testes, whereas females present a simple vaginal opening without a scrotum. Under brief anesthesia, a small ventral incision can reveal internal gonads for definitive identification.
How can the gender of mice be checked? - in detail
Determining the sex of laboratory mice requires precise observation and, when necessary, molecular confirmation. Visual assessment of external anatomy is the first step. In adult rodents, males possess a prominent, rounded scrotum and a visible penile urethral opening, while females display a smoother perineal region with a distinct vaginal opening. For juvenile mice, the ano‑genital distance (AGD) provides a reliable metric: measure the gap between the anus and the genital papilla; males typically have an AGD twice that of females. Use calipers with a resolution of 0.01 mm to record values.
When external features are ambiguous, especially in neonates, the following procedures enhance accuracy:
- Dissection of the genital ridge – under a stereomicroscope, expose the gonads; testes appear as paired white masses, ovaries as smaller, translucent structures.
- Polymerase chain reaction (PCR) – extract DNA from a small tissue sample (e.g., ear punch). Amplify the Sry gene, present only on the Y chromosome, using primers designed for Mus musculus. A positive amplification confirms a male, while absence indicates a female.
- Ultrasound imaging – apply a high‑frequency probe (≥40 MHz) to visualize internal reproductive organs without sacrificing the animal. Testes are identifiable as hypoechoic structures in the abdominal cavity of males.
- Hormone assay – measure serum testosterone or estradiol concentrations via ELISA; elevated testosterone correlates with male physiology, though overlap may occur during certain developmental stages.
For routine colony management, combine visual inspection with AGD measurement for rapid sorting, reserving molecular or imaging techniques for verification of doubtful cases. Record each determination in the animal tracking system, noting the method used, to maintain traceability and reduce misidentification errors.