Tanksley, S. D. Linkage of the genes coding for
alcohol
dehydrogenase
and
phospho-
glucomutase.
Starch gel electrophoresis of extracts from
germinating seeds has allowed determination of
linkage for the genes coding for the enzymes
alcohol dehydrogenase and phosphor-
glucomutase. For each enzyme, activity has been determined for only a single locus. F1 hybrids
between Solanum pennellii LA 716 and Lycopersicon esculentum cv. VF 36 were backcrossed to the
esculentum parent and the genotypes of the resulting seeds were determined.
Based on these data the two genes appear to be 6/115 or 5 map units apart. Segregation
data from crosses as wide as L. esculentum x S. pennellii have been shown to give linkage values less
than those from strict L. esculentum x L. esculentum crosses. Therefore the distance between the
genes might not be so small as 5 map units. The undeniable conclusion is that the two genes are
linked and probably lie within a short distance of each other. This is especially interesting since the
enzymes for which they code are both present in germinating seeds in high concentrations and both
presumably function sequentially in the same metabolic pathway converting starch (storage
carbohydrate) to ethanol with the concomitant release of ATP. At this point the evolutionary or
regulatory significance of this linkage is only conjectural.
In our initial description of the non-ripening (nor)
mutant (Tigchelaar et al., TGC 23, 1973),
preliminary evidence from F2 data suggested
repulsion phase linkage with the
Tigchelaar, E. C., and R. J. Barman Linkage of the
non-ripening (nor) and uniform ripening (u)
genes.
uniform ripening gene u on chromosome 10. Testcross data (u+/nor/u/nor+ x u/nor/u/nor) has
confirmed that nor is approximately 3.5 map units from u (Table). This close repulsion phase linkage
has provided a convenient method to identify nor heterozygotes in F2.
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