• Reproductive Parameters of Laboratory Mice (Mus musculus):
• Puberty onset (vaginal opening in females, testicular descent in males) occurs around 4–6 weeks of age.
• Full sexual maturity and optimal breeding age is reached at 6–8 weeks of age (body weight $\approx 20-25\text{ g}$).
• Breeding prior to 6 weeks is avoided to prevent small litter sizes and poor maternal behavior.
• nalysis:
• (6-8 week): Correct physiological age at sexual maturity.

Correct option: (2) 6-8 week