Mutation tlx was induced in pea by
in the homeotic gene Tl, responsible for
transformation of the upper leaflets into tendrils. Heterozygotes
possess ‘flat tendrils’ having narrow rudimentary leaf blades.
By 15 generations of selfing the line Delta was established,
in which closely linked loci Tl and His1 were
maintained heterozygous, His1 encoding the most abundant histone
The heterozygous chromosome region was flanked by several recessive markers.
The genotype of
line Delta with respect to loci His1 and Tl was:
His11. There were derived two sublines, Delta-s and
homozygous for each of the His1
alleles but heterozygous for the Tl and flanking markers. The
three lines were
compared for a number of quantitative traits, including parameters of flat
the expression of the gene Tl in heterozygote, and for recombination
the heterozygous segment. The line Delta-s exceeded Delta-f in terms of
of the first inflorescence, length of the internode 8–9,
number of pods on the main stem and mean seed mass, but was inferior regarding
number of seeds per pod. The flat tendrils were wider in the Delta-s as
compared with the Delta-f
line ; the difference was highly significant and exceeded 15% at node 17.
between the flanking markers also showed significant differences, being
highest in the Delta-f and
lowest in the Delta line. We do not exclude the possibility that the observed
differences in the
quantitative traits are caused by the substitution of alleles of the histone
H1 gene. The effects of
such substitution appeared to be especially strong for expression of the
homeotic gene Tl.