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A Maize Genetic Question

Ed Coe CoeE at missouri.edu
Tue May 2 09:12:31 EST 2000

Would it be fair to assume that 'the gene of interest' is
scored phenotypically?  If it is just being followed by
molecular sequence, or by transposon association, this
changes speculations/working-hypotheses.
Is it fair to assume that its origin traces to transposon
pedigrees?  Is the transposon coming and going, or is it
being 'modified'?

The observations open uncounted speculations, like 1) is the
SSR in B73 and other lines at a fixed place, or is it a
wanderer?  2) is chromatin added or subtracted when
recombination changes?  3) are rearrangements being
'corrected' in the region?  4) how can backcrossing lead so
quickly to local homozygosity, or does it?

There is work in the recombination literature, in addition
to a little in maize, indicating that localized homozygosity
can increase recombination.  Likely another netter will have
a better handle than I on that lit.

Check note by Chernov and Mihailov in MNL 73:
Relevant paper by Dooner and Martinez-Ferez in Genetics 1997:
Paper by Hadad et al., 1996:
Note by Maguire in MNL 64:
Paper by Nelson in Genetics 1975:

Ed Coe

Lisa Harper wrote:
>  Here is a genetic mystery (to me at least),
>          I now know of two cases where individual researchers have
>  identified an SSR within 1-2 cM of their gene of interest.  These closely
>  linked SSRs were identified in progeny of a self following an outcross to
>  B73.  Upon repetitive backcrossing to B73, the SSR gets genetically farther
>  and farther away; in one case going from 1 cM to ~25cM in one generation-
>  statistically significant with a chi-squared test.  What is happening here?
>  Have people who use marker-assisted breeding seen this?  At first, I
>  thought it was a mistake, but with two independent cases, and all numbers
>  checked for statistical significance, I think it is real.  Do rates of
>  recombination change with increased homozygosity (a hard thing to measure)?
>          Thank you for your help!
>  Lisa Harper
>  Cande Lab
>  Department of Molecular and Cell Biology
>  345 LSA
>  University of California
>  Berkeley, CA 94720-3200
>  (510)-643-8277
>  ---

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