Phenotypic stability of heterozygotes for induced chlorophyll mutations.<p>

Mertens, T. R.  <p>

R2 progenies of three chlorophyll mutations (numbers m-4, m-7 and m-8 in
the table in the above report) were grown in the fleld in Summer 1955. Data
were taken on days to first flower, first inflorescence; days to first
flower, second inflorescence; days to first ripe fruit.  Plants
heterozygous for the mutations were distinguished by progeny test.  In the
case of mutant m-7, the heterozygotes were significantly later (5% level)
than their homozygous sibs for all three traits, but the means of the
heterozygotes for the other two mutations were not significantly different
from the means of their respective control sibs.  However, for each of the
three mutants it was found that the heterozygotes had a smaller variance
than respective homozygotes, and usually the difference was significant.
The results for the mutation "netted" (m-4) are given below.<p>


Analysis of the effects of mutant m-4 in the heterozygous condition:<p>
                      variance only affected.<p>

<pre>
________________________________________________________________ 
Trait                                Difference         Variance 
measured    Genotyoe  Number  Mean   in means  Variance  ratio
________________________________________________________________ 
Days to
first flower  AA       63    79.51     0.08      6.42    2.10** 
on first      Aa       76    79.43               3.05
inflorescence         ___
                      139

Days to
first
flower on     AA       63    83.56    0.44       5.99    1.95**
second        Aa       76    83.12               3.07
inflorescence         ___
                      139

Days to
first         AA       63   111.11    0.18       6.42    2.47**
ri            Aa       76   110.93               2.60
fruit                 ___
                      139
________________________________________________________________
**  Significant at 1% level.
</pre>
     
These results are typical of the behavior of the other two mutations.  The
variance effect is quite unexpected in view of the fact that the mean is
unaffected.  The variance effect is suggestive of the greater uniformity of
hybrid corn and may be due to a genotype-environment interaction of major
proportion. It appears that heterozygotes more consistently produced the
same phenotype while homozygotes gave phenotypic response to variable
enviornmental conditions.  A more detailed analysis of this study will
appear in Genetics at some time in 1956.<p>
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