MAPPING OF A WHEAT-RYE TRANSLOCATION

Abstract

HE genetic distance of genes from their centromere remains undetected in Tconventional linkage studies. In hexaploid wheat (Triticum aestiuum L. ) these distances can be estimated by the use of telocentric stocks, as shown by SEARS (1962, 1963). The procedure involves crossing a normal stock having 21 pairs of chromosomes, bearing A , with a recessive stock in which the chromosome bearing a is telocentric for that arm. This F, is backcrossed as male to a normal recessive stock, and the recessive BC, plants are examined cytologically. As telocentrics compete poorly with normal chromosomes for transmission through the pollen, transmission of a usually necessitates its crossing over to the two-armed chromosome. Elimination of recessive BC, plants not possessing 21 pairs of normal chromosomes allows the frequency of crossing over between A and the centromere to be determined.