" Student Name: Student ID: Word count:Professor Name:Date: Assignment on Transposableelements 1 IndexTable of contents Page no.1. Introduction on Transposable elements- 3-2. Discovery of Transposable elements -3-53. Types of Transposans - 5-64. Reference- 7 2 Transposable elementsIntroduction :Much of the investigation of the classical genetics has beendevoted to the localization of genes on chromosomes. In fact most genes occupyfixed sites on the chromosomes and the overall structure of the genetic map ispractically invariant. However in early 1940?s researchers have found that someDNA sequences can actually change their position. These mobile elements have been variously called“Jumping genes”, mobile elements”, Cassettes, Insertion sequences andtransposans. The formal name of this family of mobile is transposable elementsand their movement is called transposition. The term transposon was coined by„Hedges? and Jacob? in 1974 for a DNA segment which could move from oneDNA molecule to other and carried resistance for anitibiotic ampicillin.Discovery of Transposable elements : Tranposable elements were discovered by Barbara MC Clintockthrough an analysis of genetic instability in maize(corn). The instabilityinvolved in chromosome breakage and was found to occur at sites wheretransposable elements were located. Mc Clintock used a marker gene thatcontrolled the deposition of pigmentation in the aleurone which is the outermostlayer of endosperm of maize kernels.3 Recall that endosperm is triploid, being produced by theunion of two maternal nuclei and one paternal nucleus.Mc Clintock?s marker was an allele of the C locus on theshort arm of chromosome 9. C? is a dominant allel of aleurone colorationinhibitor, any kernel possessing it will be colourless. She crossed c?c? tasselspollen with cc ears the endosperm was c?cc. Many of kernels were colourless,some showed patches of brownish purple pigments. MC Clintock gussed insuch mosaics the inhibitory c? allel has been lost sometimes during endospermdevelopment, leading to a clone of tissue that was capable of producingpigments. The geneotype in such clones would be –cc the dashindicates the lost allel c? Further study demonstrated thatc? allele is lost duringchromosome breakage.Chromosome breakage formed by transposable elementDs in maize. The allele c? on the short arm of chromosome 9 produces normalpigmentation in the aluerone. The c? indhibits this pigmentation.? The c? allele tends to be lost during cell division due to its absence,pigmentation is formed in the aluerone.? Mc Clintock established that mosaics in kernels resulted from breakageof site on chromosome 9 .4 ? She named the factor as?Ds? for „dissociation?. This „Ds? factor is carriedby „c? allele. Itself. And this Ds cannot itself capable of choromosomebreakage it is activated by „ Ac for Activation?.? These both Ac and Ds are transposable elements and they are present onthe maize genome.Types of transposable elements : Transposable elements are of mainly two types namely : 1. Prokaryotic transposable elements2. Eukaryotic transposable elementsProkaryotic transposable elements : Genetic instabilities have also been found in bacteria, and inmany cases these have led to the identification of transposableelements.Based up on the number of nucleotide pairs and their behavior thetransposans are of four types namely : a. IS elementsb. Composite transposansc. The Tn3 transposan familyd. The Transposablephages.5 "