The chromosome complement of single-pronuclear haploid mouse embryos following activation by ethanol treatment.

A technique in which mouse eggs are stimulated to develop parthenogenetically following their brief incubation in 7% ethanol in PBS is described. Very high rates of activation were achieved, and a detailed analysis presented of the class of parthenogenone which develops a single haploid pronucleus following second polar body extrusion. As preliminary studies on presumptive haploid morulae indicated that a proportion of the metaphase spreads examined had an aneuploid chromosome constitution, the incidence of aneuploidy at the first cleavage mitosis was investigated. In the control groups the level of aneuploidy was about 1%, whereas in the ethanol-treated series the incidence ranged from 13 . 6-18 . 8%. Additional pre-treatment of ethanol-activated oocytes in low osmolar medium raised the incidence of aneuploidy to 28 . 3%. Metaphase groups with 18, 19, 21 and 22 chromosomes present were observed in addition to groups with a normal complement of 20 chromosomes. The possible mode of action of ethanol in inducing parthenogenetic activation of mouse oocytes, and a high incidence of aneuploidy, is discussed in relation to previous knowledge of the action of this agent. Preliminary studies using G-banding indicate that the aneuploidy observed appears to arise as a result of non-disjunction which may involve any of the chromosomes of the complement.