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Lecture notes of 14 pages for the course Transmission Genetics at QMUL
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Transposable elements in health and diseasesLearning objectives:
1. Structure and types of transposons
2. Their role in health and diseases
What are transposable elements?
Mobile DNA segments that can move from one side of the genome to another
- sometimes creating or reversing mutations and altering the cells genetic identity and genome size
First identified by Barbara mc Clintock who won a Nobel prize
- She looked at corn chromosomes
‘jumping elements’
TE regulate own transcription
The experiment done by McClintock to study transposable elements and its effect on phenotype
The Dc and Ac elements of maize were the first example of transposons
- Ac = Activator element
- Dc= dissociate element
McClintock identified many unusual feature of corn chromosome
- She noticed that in 1 set of corn chromosome, chromosome 9 tended to break at a high rate at chromosome
breakage sites
- She termed the chromosome breakage sites as transposon sites Transposable elements are inserted into the
transposon sites.
4 chromosomes
- 1st chromosome is just showing the chromosome labelled
- 2nd chromosome gives rise to red kernels because the colour locus is up
- 3rd chromosome shows that the chromosome breakage site is positioned inside the C locus = colourless kernels
- 4th chromosome shows that the transposable element has been removed from the C locus = coloured kernels due
to transposable elements moving to
different positions and effecting
expression of the genes
, In this way, McClintock identified 20 independent cases in which Ds has moved to a new chromosome location.
- Thus Ds is a transposable element
She also found that a second locus termed Ac (for activator) was necessary for Ds to move
- Ac encodes the enzyme transposase
When McClintock published these results in 1951 they were met with great skeptism
- ‘DNA was stable and permanent and not susceptible to rearrangement’
Over the next several decade, the scientific community realised that TEs are a widespread phenomenon
- McClintock was awarded the Nobel prize in 1983
- She is the only women to receive an unshared Nobel prize in her category
Transposition pathways
TE are found in all living organisms
Many transposable elements have been found in bacteria, fungi, plant and animal cells
3 general type of transposition pathways have been identified
1. Simple or conservative transposition
2. Replicative transposition
3. Retrotransposition
Image shows different species and their composition of TE
LO1. STRUCTURE AND TYPES OF TRANSPOSONS
DNA transposons
1. Simple transposition
- ‘cut and paste’
- Widely found in bacteria and eukaryotes
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