Mobile Genetic Elements

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.

This is our friend Oliver the parrotlet,

Oliver is a true parrot,

the smallest in the world.