Post on 18-Jan-2016
description
Genetics in life, love and lab
Spontaneous mutation at low levels is normal
Fly homeotic (Hox) selector gene mutations : cool
Antp
Ubx
Antennapedia
UltrabithoraxLoss-of-function (lof)
Mutated gene DNA, modified fly
proboscipedia
Ultrabithorax
What is DNA, Stephen?
Chromatin
From: Felsenfeld et al., 2003
open
closed
1 m
1 µm
A
a
A
aA
a
A
a
2n4n
2 x 2n
Mitosis: one mother cell becomes two daughter cells
2 x ‘2n’
A
a
2n
A
a
4n
a
A
A
A
a
a
4 x 1n (gametes)
Meiosis: one mother cell becomes four gametes
DNA double helix
A T A G G G C C T C A C A CA G C A T
T A
4 building blocks: A, T, G, C
A T A G G G C C T C A C A CA C A G C A T
T A T C C C G G A G T G T G T G T C G T A
Mutations e.g. stutteringDNA polymerase
2 x 2n
A
a
A
a
2n
A
a
4n
A
a
16 x 2n
256 x 2n
Incomplete mitoses give giant chromosomes
Giant chromosomes of Drosophila and cytogenetics
We can see rearrangements such as inversion loops
Amniocentesis, A pre-natal test for high-risk pregnancies
A karyotype for a human cell (e.g. amniocentesis)
Trisomy for chromosome 21
Protein
Gene functio
n
A Cystic Fibrosis (mucoviscidose)-bearing family tree
I
II
III
IV
The family tree The family tree reveals the reveals the recessiverecessive nature nature of the disease of the disease
The disease The disease appears in the appears in the offspring of offspring of two apparently two apparently healthy healthy individualsindividuals
Two sick childrenTwo sick children
A quick detour concerning positional cloning
.
six genotypes (AA, AO, BB, BO, AB, & OO) &
four phenotypes (A, B, AB, O)
As a function of which protein form – A, B, A and B, or neither of these – is expressed
A B O
A marriage between AB and O parents
A B x O O
½ A ½ B
O ½ AO (A) ½ BO (B)
Frequency of I - locus alleles
Allele IA IB IO
Frequency 0.4 0.1 0.5
Frequency of ABO blood types
Phenotype A B AB O
Genotypes IAIA & IAIO IBIB & IBIO IAIB IOIO
Frequency 0.56 0.11 0.08 0.25
But in a population…
Frequencies of MN blood types
MM MN NN f (M) f (N)
US Whites
0.29 0.50 0.21 0.54 0.46
Now for a different blood type marker:
Frequency of MN blood types
MM MN NN f (M) f (N)
US White
0.29 0.50 0.21 0.54 0.46
Product Rule: probability of two events occurring together is the product of their separate probabilites
So, the probability of AB and N blood types = f(AB) x f(NN) = (0.08) x (0.21) = 0.0168 (<2%)
Phenotype A B AB O
Genotypes IAIA & IAIO IBIB & IBIO IAIB IOIO
Frequency 0.56 0.11 0.08 0.25
The Experts…
A T A G G G C C T C A C A CA C A G C A T
A T A G G G C C T C A C A CA G C A T
A T A G G G C C T C A C A CA C A C A G C A T
A T A G G G C C T C A C A CA C A C A C A G C A T
0.31
0.32
0.14
0.23
Allele / DNA variant Allele frequency
The Experts always get their man !
Jumping genes
Normal instability:
Mirabilis jalapa
Transposable elements interrupt the chromosome and jump around
Bad genes run in families
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Los Angeles
Incidence of a genetically transmissible syndrome: LA
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Tokyo
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Incidence of a genetically transmissible syndrome: Tokyo
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Incidence of a genetically transmissible syndrome:
Iceland
A Cystic Fibrosis (mucoviscidose)-bearing family tree
I
II
III
IV
The family tree The family tree reveals the reveals the recessive nature recessive nature of the disease of the disease
The disease The disease appears in the appears in the offspring of offspring of two apparently two apparently healthy healthy individualsindividuals
Two sick childrenTwo sick children
In this family, the affected children come from a marriage between two first cousins, each of whom is a carrier.
‘Blood’ marriage
Homozygosis makes for bad blood
Victoria of England Nicolas II and Alexandra of Russia
Rasputin
Intermission