The allele the short arm chromosome produces normal pigmentation the aluerone
Transposable elements
Introduction :
Recall that endosperm is triploid, being produced by the union of two maternal nuclei and one paternal nucleus.
Mc Clintock’s marker was an allele of the C locus on the short arm of chromosome 9. C’ is a dominant allel of aleurone coloration inhibitor, any kernel possessing it will be colourless. She crossed c’c’ tassels pollen with cc ears the endosperm was c’cc. Many of kernels were colourless, some showed patches of brownish purple pigments. MC Clintock gussed in such mosaics the inhibitory c’ allel has been lost sometimes during endosperm development, leading to a clone of tissue that was capable of producing pigments.
She named the factor as’Ds’ for ‘dissociation’. This ‘Ds’ factor is carried by ‘c’ allele. Itself. And this Ds cannot itself capable of choromosome breakage it is activated by ‘ Ac for Activation’.
These both Ac and Ds are transposable elements and they are present on the maize genome.
Prokaryotic transposable elements :
Genetic instabilities have also been found in bacteria, and in many cases these have led to the identification of transposable elements.Based up on the number of nucleotide pairs and their behavior the transposans are of four types namely :
IS elements : These IS elements are simplest bacterial transposans and IS means insertion sequence. They contain less than 1500 nucleotide pairs. These are compactly organized.
There is a single coding sequence with short identical (or) nearly identical sequences at both ends.
IS elements integrate episomes in to bacterial chromosomes.
Composite transposans :
