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Abstract
It was found that all genetic variants for glaucousness over the whole
plant involved genes on the chromosomes of group 2. Of three recessive
nonglaucous lines which arose spontaneously in Chinese Spring background,
all were found to be due to deletion or mutation of the gene for glaucousness
on chromosome 2B.
Another recessively nonglaucous line which arose in the backcrossing of
the inhibitor gene of C.W.S. 5075 into Chinese Spring background was found
to have undergone a large terminal deletion of the short arm of chromosome
2B.
Chromosome 2D in Chinese Spring was found to bear a weaker gene homoeologous
to that on chromosome 2B. It was found that chromosomes 2A bears no gene
affecting glaucousness.
Two dominant ethyl methanesulfonate induced nonglaucous mutants were identified
as alleles of the inhibitor gene on chromosome 2B.
The variety Mentana was found to have no fully effective group-2 genes for
glaucousness. The recessive gene for nonglaucousness on chromosome 2B of
Mentana was mapped as lying between 33 and 50 map units from the centromere.
A linkage stu~ gave no recombinants between the Mentana gene and the
inhibitor gene from 5075, giving a maximum distance of 8 map units between
them. There is a strong case for thinking that both genes are alleles of
the Chinese Spring gene for glaucousness.
Genes capable of interacting to modi~ the dominance relationship of the
2D inhibitor were found in the ABD XIII background Poso. It was found that
an extra dose of chromosome 2B could interact with the genes of ABD XIII
to give the same effect as the Poso genotype. Modifier genes in the backgrounds
of Poso and 5075 also interacted to alter the dominance of the 2B
inhibitor.
Group 3 chromosomes were found to bear genes specifically for glaucousness
of the peduncle. Chromosome 3A bears the most effective gene, chromosome
3B a less effective one and chromosome 3D apparently bears a null allele.
Both Poso and Mentana were found to have genes which could substitute for
the chromosome 3A gene of Chinese Spring.