Homozygous and heterozygous homologous chromosomes: effects on preferential pairing and recombination frequency in wheat

Trisomics for chromosomes 1A and 6B of wheat backcrossed to euploids showed progeny with unexpected segregation frequencies (cytological and genetical) that can be attributed to preferential pairing between homologues. Recombination frequency between the centromere and a gene for mildew reaction of chromosome 1A showed an increase from the first to the second backcross that could be attributed to a positive correlation between homozygosity and the degree of pairing between homologous chromosomes. The use of wheat trisomics for genetic analysis is also discussed.Key words: preferential pairing, trisomic segregation, wheat cytogenetics, recombination frequency, pathogen reaction.