In
genetic studies of corn (Zea mays) Barbara
Mc Clintock found a gene that caused spots on kernels due to the breakage
of chromosomes. She called this gene dissociator (Ds). She found a second gene
activator which had to be present to cause Ds to break the chromosome. Activator
could jump from chromosome to chromosome. Dissociator could only jump when activator
was around.
The explanation
was that the genes were transposable
elements.
Ac coded
for a transposase and was contained as a mobile element.
Ds was
a defective transposon because it lacked transposase. Thus, Ds could only
move when Ac provided the enzyme transposase.
What does it mean to say that Ac is a trans acting factor? Why (how) is it trans acting?
Significance
of Barbara Mc Clintock's contributions to genetics were many.
This work
was the first documentation of one gene controlling another i.e.. the basis
and concept of regulatory genes.
Second
this work proved that genes could move i.e. defined mobile genetic elements.
Barbara
Mc Clintock had provided a significant proof of the chromosome theory by demonstrating
that crossing over was breakage and fusion of chromosomes.
Barbara
Mc Clintock developed the best techniques for studying chromosomes in plants.
Text iGenetics by Peter J. Russell
This web site is provided for instruction in Botany and Zoology 342
by Kenneth G. Wilson,
Professor of Botany
Miami University
wilsonkg@muohio.edu
