|
2. Transmission of monosomic condition: Since 1955 data
on transmission of monosomic condition through female
gametes have been accumulated for the variety Chinese
Spring.
Monosomic condition was more readily transmitted in
homoeologous group 3 than in groups 2, 7, 6 and 4, while the
transmission rate of group 2 was significantly lower than
those of groups 1, 5 and 3. In order to test the differences
among the three homoeologous chromosomes of a group,
chi2-values for intragroup heterogeneity were
calculated. Homoeologous chromosomes of groups 2, 3, 4, 5
and 7 behaved similarly, while differential transmission was
found for groups 1 and 6. The transmission rates for
chromosome I of group 1 and for chromosome X of group 6 were
significantly lower than those found for their homoeologues.
This fact indicates that chromosomes I and X have been
differentiated from their homoeologues in respect to the
transmission rate of monosomic condition.
3. Heading date: Spring - type alleles of major growth -
habit genes are almost completely dominant over their winter
- type alleles under a long day condition. Based on this
fact, the effect of a chromosome of a winter variety on its
heading can be quantitatively estimated from the difference
between the heading dates of disomic and monosomic
F1's which are obtained from crosses, Chinese
Spring monosomics (female) x winter variety. Four winter
varieties, Malakov, Hussar, Mediterranean and Democrat were
crossed with 21 monosomic lines of Chinese Spring and the
heading dates of the respective disomic and monosomic
F1's were investigated.
In both cases chromosomes IX and XVIII of winter varieties
had a great effect on delaying heading, the latter's effect
being about three times as much as the former's, The effect
of chromosome V in Malakov and other varieties was almost
the same as that of their chromosome IX in Misima, while no
effect of the former was found in Winnipeg for Elgin and
other varieties. This discrepancy between the two data is
not explainable at the present. However, it is noteworthy
that the three chromosomes, V, IX and XVIII belong to the
same homoeologous group and retain the same function in
delaying heading, though their effects are quantitatively
different.
4. Review of other results: So far as awn development is
concerned, three homoeologous chromosomes of groups 2 and 3
have a similar function, namely, promotion and modification
of awn development, respectively. No homoeology exists among
four epistatic awn - inhibitors. There is also no homoeology
among genes which control hairiness, spike morphology or
necrosis, while a partial homoeology is found among genes
which control red pigmentation of different plant organs. A
gene, v on chromosome III controls seedling
virescence, causing semi - lethality of plants. Its
homoeologous chromosomes, XII and XVI are known to carry
genes, which interact with v, causing seed lethality.
This fact indicates that these three chromosomes have a
similar function. As to disease resistance, no homoeology in
function seems to exist among homoeologous chromosomes,
because an apparent similarity between some homoeologous
chromosomes can be reasonably explained by coincidence due
to chance.
|