Summary
The induction of large (L) and small (S) genotrophs by the environment from the plastic (PI) genotroph is accompanied by changes in a gene determining hairy (H) and hairless (h) septa in the capsules. S and PI are HH, L is hh. The heterozygote Hh is unstable and three heterozygous classes, I, II, III, are recognisable in the F2 with approximately 30, 40, 50 hairs per septum. H-→h and h→H changes occur and class III F2 Hh heterozygotes with the highest hair numbers give H:h ratios in F3 of about 6:1. Selection of class III F2 Hh heterozygotes also selects for Hh plants with a high Hh→HH potential, but only about 33 per cent, of these F2 plants have this potential in so far as it leads to an overt and immediate change of Hh→HH by the next generation. In the F3 of L×S and S×L crosses a further proportion of Hh heterozygotes has the Hh×HH potential, but not in the Pl×L and L×Pl crosses. Thereafter no further changes are found. The fade-out in F3 and F4 may be due to stabilisation at the locus or of associated factors, to the different environments in which the generations are grown, or because selection of class III was discontinued after F2 and all three heterozygous classes reappeared in F3. These orderly, high-frequency changes occur in the Hh heterozygotes only, and are probably essentially the same as paramutation in maize.
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McLellan, J., Durrant, A. Instability of Hh heterozygotes in flax genotrophs. Heredity 30, 63–71 (1973). https://doi.org/10.1038/hdy.1973.7
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DOI: https://doi.org/10.1038/hdy.1973.7
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