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Lecture 16

HMB265H1 Lecture Notes - Lecture 16: Gene Knockout, Cloning, Pigment


Department
Human Biology
Course Code
HMB265H1
Professor
Maria Papaconstantinou
Lecture
16

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Lecture 16: Transposable Elements
Positional Cloning
- Tomato plants
- Metaphoric description using colour that gives us a description of how much of a certain
DNA is in a certain plant
- First plant is all grey (the plant has the DNA of that particular strain)
- Second plant is black (the pants has DNA from a different strain)
o Can distinguish between the strains
- One plant has a particular trait that we want to isolate for
- One plant has the trait for a big tomato
o Cross this plant with a strain for tiny fruit
- In the F1 generation
o 50% of the DNA from each parent
can have big fruit, small fruit and everything in between
- we only want the big fruit gene isolated
o only pick the big fruit plant (black DNA)
- cross the big fruit plant with the tiny fruit again (back cross)
o more tiny fruit DNA
o 75% of tiny fruit DNA and 25% big fruit DNA
narrowing down the region of where that gene resides for big fruit (25%)
- continue to back cross the big fruit plants until 99% of the DNA is for the tiny plant
o everything BUT the fruit size will come from the tiny fruit plant DNA
o the fruit size will come from the parental black DNA for the big fruit
Transposition
- Movement of small segments of DNA called transposable elements
from one position to another in the genome
- Have evolved the ability to move in the genome
o Jumping genes
- Can insert themselves into open reading frames and knockout genes
- Can excise other genes
- Make certain genes more mutable than others
- Disoered  Barara MClitok i late ’s aarded Noel Prize i 
o Scientists did not agree with her work as it did not align with the chromosomal
theory of inheritance
- Corn: transposable element of pigment genes when it is inserted into the gene the
colour can be inserted or knocked out
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Trasposale eleets TE’s are ovale geeti eleets
- TE’s are a seget of DNA that eoles the ailit to oe fro place to place within
a genome
- Marus Rhoades ’s) and Barbara McCClintock (1940-’s iferred eistee of
TE’s fro geeti studies of or
o Barbara performed genetic experiments
- TE’s hae o ee foud i all orgaiss
o Scientists were able to clone the transposable elemetns and then realize that
they were in the genomes of all organisms
o Human genome contains 44% of transposable elements
- Previously considered to be selfish DNA carried no genetic information useful to host
- No ko that soe TE’s hae eoled futios that are eefiial to host
o Drosophila to not have repeats in their telomeres
o Transposable elements insert themselves into the chromosomes and maintains
the size of the chromosomes (beneficial)
- TE length ranges from 50 bp to 10 kb
- TE’s a preset i hudred of thousads of opies per genome
MClitok’s experiets
- One strain of corn frequently had break in chromosome 9
- Ds element helps cause break
- Another element Ac required to activate break at Ds locus
- Dissociation locus
o In order for this to happen another element
(activator) must be present for the break to happen
- Used visual markers to test her theories
- Chromosome 9 had 3 different markers (all dominant)
o Pigment marker
o Plump
o Starchy
This was the wild type phenotype
- If chromosome 9 had all recessive phenotypes
o Plant was colourless, shrunken, and waxy
- Noticed some plants that were colourless plump and starchy
- Dissociation Locus (Ds): nonautonomous element
o Completely dependent on the Ac
- Activator Locus (Ac) autonomous element
- Autonomous elements encode information required for own movement and for
movement of nonautonomous elements
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