Linkage studies of the h gene with plant weight in flax genotrophs.

The association of the H-h (hairy-hairless septa) character with plant weight was studied in the coupling and repulsion phases in F2 of reciprocal crosses between large (L) and small (S) genotrophs of flax variety 'Stormont Cirrus'. F2 plants of reciprocal crosses in coupling (L(H) x S(h)) and in repulsion (L(h) x S(H)) giving H-h segregations were grown with their parents at two sowing times. Significant positive and negative associations between h and plant weight were obtained. A model is proposed based on the hypothesis that the H phenotype had changed to the h phenotype at the time of induction by a heterochromatic region extending over this locus. In the heterozygote, stable equilibria of the homozygotes are destroyed and transfer of heterochromatin, or number of reiterated sequences, or a decrease in one homologue and an increase in the other, occur in this region between homologous chromosomes. The amount and direction of the association is dependent upon the frequency of transfer: 0% transfer gives complete positive association; 50% transfer, no association; 100% transfer, complete negative association. This mechanism or heterochromatic transfer preserves the Mendelian ratio of 3∶1 of H∶h in the F2. It is also supposed that there must be other controlling elements present as well.