What sexes do mice have? - briefly
Mice exist as either male or female, with sex determined by the presence of XY (male) or XX (female) chromosomes. No other sexual forms occur naturally in laboratory or wild mouse populations.
What sexes do mice have? - in detail
Mice exist as two primary biological sexes, male and female, determined by the presence of sex chromosomes: XY for males and XX for females. The chromosomal configuration initiates development of gonads, which differentiate into testes in XY embryos and ovaries in XX embryos. Hormonal signals from these gonads shape secondary sexual traits and reproductive physiology.
Males possess testes that produce sperm and secrete testosterone, which drives the development of the penis, scrotum, and accessory glands such as the seminal vesicles and prostate. Testosterone also influences muscle mass, aggression, and territorial marking. In laboratory strains, males typically weigh 20–30 % more than females of the same age.
Females develop ovaries that release oocytes and secrete estradiol and progesterone. The estrous cycle lasts approximately 4–5 days and progresses through proestrus, estrus, metestrus, and diestrus, each characterized by distinct hormonal profiles and vaginal cytology. Female reproductive anatomy includes the uterus, two uterine horns, and a vagina, enabling implantation of multiple embryos per gestation. Gestation lasts about 19–21 days, followed by a lactation period of 2–3 weeks.
Occasional intersex individuals arise from genetic mutations, chromosomal anomalies (e.g., XO, XXY), or experimental manipulation of sex-determining genes such as Sry. These mice may display ambiguous gonadal tissue, mixed secondary characteristics, or infertility, and are valuable for studying sex differentiation pathways.
Key distinctions can be summarized:
- Chromosomes: XY (male) vs. XX (female)
- Gonads: Testes vs. ovaries
- Primary hormones: Testosterone vs. estradiol/progesterone
- Secondary anatomy: Penis/scrotum vs. uterus/uterine horns
- Body mass: Males heavier on average
- Reproductive cycle: Continuous sperm production vs. 4–5 day estrous cycle
Understanding these biological differences is essential for experimental design, animal husbandry, and interpretation of sex‑specific data in biomedical research.