ANALYSIS OF CHIASMA FREQUENCY AND 1ST MEIOTIC SEGREGATION IN A HUMAN MALE RECIPROCAL TRANSLOCATION HETEROZYGOTE, T(1,11)(P36.3,Q13.1), USING FLUORESCENCE INSITU HYBRIDIZATION

In this study we have used a testicular biopsy from a human male with a 46,XY,t(1;11) (p36.3;q13.1) karyotype. Fluorescence in situ hybridisation with whole chromosome libraries and paracentromeric probes were applied to identify normal and derived chromosomes 1 and 11 in both first metaphase (MI) and second metaphase (MII) cells. The chiasma frequency distribution was established in the quadrivalent. A large proportion of MI cells was found to have at least one interstitial chiasma, resulting at MII in dimorphic chromosomes bearing one normal and one translocated chromatid. Alternate, adjacent I, adjacent II, and 3:1 products were all identified at MII. More than half of the cells analysed could not be assigned to a single segregation category because of the presence of interstitial chiasmata. Such MII cells could have arisen from either alternate or adjacent I segregation. We also calculated the proportion of sperm expected to be normal, balanced, and unbalanced. The latter data are in agreement with the results reported by Spriggs et al. (I 992), who karyotyped sperm from the same individual.