Meiotic effects in chromosomally derived male sterility of mice

Much sterility in male (though not in female) mice can be related to the presence of specific types of chromosome anomaly. These include the XXY and XYY conditions, failures of association of X and Y, heterozygosity for reciprocal translocations involving the X or Y chromosomes as well as some which involve autosomes only, tertiary trisomic derivatives of these and certain multiple Robertsonian translocations. In all of these the sterility stems from a defect of spermatogenesis, which leads to the production of few or no spermatozoa. Studies of reciprocal translocations are of particular value for elucidating the mechanisms involved becausa different ones exhibit an almost complete range of effects, from those with normal sperm production to those in which spermatogenesis stops at the onset of meiosis. Between these extremes a number of characteristic patterns can be discerned but in general the cessation of spermatogenesis tends to be graded rather than abrupt. The effects on spermatogenesis are associated with special characte- ristics of the translocations themselves, namely a tendency for one point of exchange to be close to (or even within) centromeric heterochromatin and the other fairly distal on the chromosomes involved. This frequently leads to the formation of long and short mar- ker chromosomes and to the production of viable tertiary trisomic mice, which are also male-sterile as a rule.