PACHYTENE PAIRING AND OOCYTE NUMBERS IN MICE WITH 2 SINGLE ROBERTSONIAN TRANSLOCATIONS AND THE MALE-STERILE COMPOUND WITH MONOBRACHIAL HOMOLOGY

Oocyte numbers and synaptoncmal complexes were studied in two Robertsonian translocations. Rb(6.15)1 Aid and Rb(4.6)2Bnr. and their male-sterile compound. Oocyte numbers in the compound were lower than those of either parent, and there was a marked difference between reciprocal crosses. Synap-tonemal complexes of homozygous females appeared as 19 biva-lents. those of single hcterozygotes as 18 bivalenls and a trivalent. and those of compound heterozygotes as 17 bivalenls and a quadrivalent. Most trivalents were fully paired, whereas the majority of quadrivalents exhibited terminal asynapsis. About one-half of all oocytes had other pairing abnormalities, probably reflecting reduced survivability. Whereas all fully paired quadrivalents were present in cells not showing any pairing anomalies, one-half of the quadrivalents with terminal asynapsis were seen in oocytes with other anomalies. It is suggested that in oocytes destined for atresia. there is a predisposition to synaptic failure of translocation configurations. Additional oocytes are likely to break down because of the deleterious effect of the compound translocation on gametogenesis. This effect seems to be more pronounced in Rbl Aid Rb2Bnr spermatocytes than in oocytes. © 1990 S. Karger AG, Basel.