Chromosomes of Mouse Embryos and Newborn Young: Preparations from Membranes and Tail Tips

Abstract

Chromosome preparations can be obtained from the membranes of midterm mouse embryos allowing the embryos themselves to be preserved for other investigations. Whole implants are dissected from the gravid uterus and exposed to 2 × 10⁻⁷ M Colcemid in TC medium 199 for 1 hr at 20–25 C. The membranes are removed, placed in 1% Na₃-citrate at the same temperature for 4–12 min depending on gestational age, fixed in 3–4 ml of a 3:1 ethanol-acetic acid mixture for 1 min to 3 hr and transferred to 0.5 ml aqueous 60% acetic acid for 4 min. Cells detach from the membranes into the acetic acid. Chromosome spreads are then obtained by drying the acetic acid on heated slides. The method can be modified for tail tips of newborn young. Embryos on the 8th to 18th day of gestation and 1- to 6-day-old mice are suitable. (On the 8th to 10th days, preparations are made from embryo and membranes combined.) Preparations ready for scoring can be obtained from foetal membranes in 90 min and from tail tips in 150 min.