Analysis of the T(3;?)6 Ca and T(14;17)264Ca translocations in the mouse by quinacrine mustard staining

Ethanol-induced chromosomal abnormalities at conception

Preliminary findings have indicated that mouse eggs exposed briefly in vivo or in vitro to a dilute solution of ethanol activate parthenogenetically. Cytogenetic analysis of the first-cleavage chromosomes of haploid parthenogenetic embryos indicated that up to 20% of this population were aneuploid as a result of non-disjunction. Anaesthetics also can induce parthenogenesis of rodent eggs, and in studies using anaesthetics, colchicine and colcemid, abnormal chromosome segregation and heteroploidy of rodent embryos have been observed. I now report that when recently mated female mice are given a dilute solution of ethanol by mouth, non-disjunction can be induced in the female-derived, but apparently not in the male-derived, chromosome set of fertilized eggs. Taken together, these findings suggest that ethanol consumption (as well as exposure to other 'spindle-acting' agents) at the time of conception may be the cause of certain types of chromosomal defects commonly observed in human spontaneous abortions.

Identification of the mouse chromosomes by microdensitometry

Densitometric analysis has been performed on mouse chromosomes from "in vivo" preparations stained with Giemsa after trypsinisation. The characteristic curves obtained by analysing the same chromosome after different durations of trypsinisation suggest that a trypsinisation step is not always necessary to get an analysable banding pattern. The best results are obtained when the chromatids are long and closely appressed and by analysing the positive photomicrographs.

The incidence of chromosomally unbalanced gametes in T(14; 15)6 Ca heterozygote mice

When T6/+ female mice were mated to non-translocation-bearing males, the relative viability of the embryos at 13·5–14·5 days gestation was about 39%. About 36% of the oocytes ovulated by T6/+ females were aneuploid, as a result of non-disjunction at meiosis, the majority having either 19 or 21 chromosomes. However, aneuploidy only accounts for a proportion of the embryonic loss in T6/+ × +/+ matings, as many of the embryos with 41 chromosomes survive postnatally. The present findings indicate that approximately 50% of the oocytes ovulated with the normal haploid number of chromosomes (n= 20) were genetically unbalanced as a result of adjacent segregation, and that a high proportion of the resultant embryos die in the early postimplantation period. In the present study non-translocation-bearing mice which were genotypically similar to the T6/+ females acted as controls.

Translocation trisomic mice: production by female but not male translocation carriers

In man, there is generally a greater chance for a translocation trisomic child to be born if the mother rather than the father is the translocation carrier. The same type of inheritance has occurred in the mouse. Female mice heterozygous for the reciprocal translocationT(14;15)6Ca have produced a high frequency of translocation trisomic offspring. Male mice heterozygous for the same translocation have produced no translocation trisomic offspring. Thus, the laboratory mouse may provide a model for studying the cause of this phenomenon.

Chromosome mapping in the mouse, fluorescence banding techniques permit assignment of most genetic linkage groups

Chromosome banding techniques have permitted the identification of every normal chromosome in the mouse, Mus musculus, and the demonstration of strain differences. By identifying the chromosomes involved in a series of translocations, it has been possible to assign 14 of the 19 known linkage groups to 14 different chromosomes. These powerful cytological methods promise to revolutionize cytogenetic studies in higher organisms.