Chiasma frequency and position in male and female mice of chromosomes involved in homozygous and heterozygous translocations and tertiary trisomy

Abstract

Chiasma frequency and position were analyzed at a predominantly late diplotene-diakinesis stage of the first meiotic division in oocytes and spermatocytes from T(1;13)70H homozygotes and heterozygotes, T(2;8)26H heterozygotes and from Ts(I13)70H tertiary trisomics of the mouse, Mus musculus. For T70H/T70H, the 131 long marker bivalent was studied and for the other karyotypes, analysis was confined to the multivalent configurations adopted by the rearranged chromosomes and their homologues. For the 131 bivalent, the chiasma frequency tended to be increased in the female. For the T26H and the T70H multivalents, the chiasma frequencies were higher in the female, largely due to the much higher values in the short interstitial segments. This observed enhancement has been attributed to pairing differences rather than to differences in chiasma forming capability. Both in the telomeric region of the 131 bivalent and in the short translocated segments of the reciprocal translocation and tertiary trisomic multivalents, females showed fewer chiasmata than males. The determinations of chiasma position in the 131 bivalent indicated chiasma interference with respect to position, leading to clustering of chiasmata somewhat beyond the centromere and towards the telomere of this chromosome.