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Lecture 3

BIOB11H3 Lecture Notes - Lecture 3: Microtubule, Restriction Enzyme, Escherichia Coli

Biological Sciences
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Dan Riggs

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BIOB11- Lecture 3- Genome Evolution and Introduction to the Central Dogma of Molecular Genetics
Gene mapping, Figure 10-30
Things that can happen - during unequal crossing over.
Fuzzy chromosome imageSame chromosome but one has suffered an inversion
Some cancers are due to inversions etc. on a chromosome
Mobile genetic elements: Transposons
•Transposon/transposable element
-transposition means change of position from one place to another.
Barbara McClintock: „controlling elements of maize (corn)‟ Nobel prize in 1983
Experiment: gene C (corn)
A transposable element is inserted into the color gene at make it a colorless kernels.
Can this transposable element now jump out of the gene?
If late then some purple some clear (spot)

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If it is out early in development then mostly purple
-Larger sectors due to transposon jump early in development
Transposable elements do not have a goal site, they can jump into a random site (called recipient or target
-no need to memorize random (AATTC) sequence.
-the transposon inserts into the recipient DNA
-the ends of the transposon are comprised of inverted repeats (in red)
Inverted repeat the same sequence from 5‟ to 3‟ but arranged in a inverted order (flipped horizontally and
Direct Repeat- the same sequence from 5‟ to 3‟ in the same direction and order
The transposon has a protein that recognizes the inverted repeats so if it need to jump somewhere else, the
protein recognizes that it need to collect all the DNA between the two inverted repeats.
The inverted repeats are flanked on either side by the direct repeats
Generation of Direct Repeat
1. First find a sequence target site
2. The enzyme transposase encoded by the transposon which acts on DNA and makes staggered cuts
3. the end structure has a partial single stranded structure hanging
4. The transposon then enters the gap and host enzymes come in and repair the DNA using the
complementary base pairs of the end structures creating a direct repeat sequence.
- this is like a “cut and paste method”
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