gee ce

ES HORTICULTURAL INSTITUTION
_ » » * Bayferdbury, Hertford, Herts. |

 

ao

 

a wp

Dear Dr. Lederberg, & os

  

 

eee” Thank you very much for your interésting letter.
and for your interesting explanation of the "tempor: tat
Tam sorry that.the Annual Report, of necessity, gave such an
inadequate account, But .a ‘description and discussion of

the data should have appeared in "Heredity" by now.

~>> -In-vanswer.to your question about the relative actions

on the pollen phenotype of the generative and vegetative nuclei, —
I agree that it seems probable that the vegetative nucleus plays |
the major role but I know of no real evidence for this, The work
of Newcombe (J. of Genet 194% Find my own unpublished work show .
that most of the pollen physiology is laid down before the division
into the vegetative and generative nuclei, Furthermore, incompat-
ibility seems to be laid down:even earlier; mutations from X-rays
_ given just agter tetrad formation, which must be presumed to occur,
have no effett on the immediate pollen phenotype. Despite this: -
your explanation would still hold if the gene were behaving towards
X-rays as if it were reproduced at this early stage ready for
pollen grain. division, »

But I have six families of plants derived from X-rays
which contain more than three plants, and these could not have
arisen by a mutation in the vegetative nucleus alone.

. An. alternative to the "temporary" mutation
explanation,as I see it,is that a change might have occurred in a
possible cytoplasmic factor that is necessary for 5 gene express-
ion. Such a hypothetical factor would have to be common to all
the alleles otherwise if there were different factors specific
to each S allele one would expect, due to irregular segregation
of the cytoplasm at meiosis, the whole system to breakdown,

With such a common cytoplasmic factor, both of
the S alleles of the diploid should pass the sieve and this would
result in families with both S homogygotes.

As yet none have been found but the numbers are small
and further tests, which are“in progress, are necessary before
thf% occurrence can be excluded.

_ Realizing that the "temporary" mutations would cut
right across some of the orthodox concepts, I am cautious about
it until further data are obtained,

Yours sincerely,

TT SD

 

ry" mutations, ~ =

i in MEE ane nc vate