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Genetics in life, love and lab. Spontaneous mutation at low levels is normal. Antp. Ubx. Fly homeotic (Hox) selector gene mutations : cool. Antennapedia. Ultrabithorax Loss-of-function (lof). Ultrabithorax. proboscipedia. Mutated gene DNA, modified fly. What is DNA, Stephen?. 1 m.
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Antp Ubx Fly homeotic (Hox) selector gene mutations : cool Antennapedia Ultrabithorax Loss-of-function (lof) Ultrabithorax proboscipedia Mutated gene DNA, modified fly
1 m Chromatin open closed 1 µm From: Felsenfeld et al., 2003
A A A A a a a a Mitosis: one mother cell becomes two daughter cells 2n 4n 2 x 2n
A A a a A A a a A a 2n 4n Meiosis: one mother cell becomes four gametes 2 x ‘2n’ 4 x 1n (gametes)
A T A G G G C C T C AC ACA G C A T T A A T A G G G C C T C AC ACAC A G C A T T A T C C C G G A G TG TG TG T C G T A DNA double helix 4 building blocks: A, T, G, C DNA polymerase Mutations e.g. stuttering
A A a a A A a 256 x 2n a 2n 4n 2 x 2n 16 x 2n Incomplete mitoses give giant chromosomes
Giant chromosomes of Drosophila and cytogenetics
Amniocentesis, A pre-natal test for high-risk pregnancies
A karyotype for a human cell (e.g. amniocentesis) Trisomy for chromosome 21
Protein Gene function
A Cystic Fibrosis (mucoviscidose)-bearing family tree I The family tree reveals the recessive nature of the disease The disease appears in the offspring of two apparently healthy individuals II III IV Two sick children
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
O AB
A marriage between AB and O parents ABxO O ½ A ½ B O ½ AO (A) ½ BO (B)
ABO blood groupsIsoagglutinin locus (I) on Chromosome 9 has three alleles: IA , IB , IOA & B alleles are co-dominant: both are expressed in the blood group phenotypeA & B alleles are dominant to O : AA, AO & BB, BO indistinguishable Matings ("marriages") between males & females produce Genetics of ABO phenotypes But in a population… Frequency of I - locus alleles Frequency of ABO blood types
Now for a different blood type marker: Frequencies of MN blood types
Frequency of MN blood types Product Rule: probability of two events occurring together is the product of their separate probabilites So, the probability of ABand N blood types = f(AB) x f(NN) = (0.08) x (0.21) = 0.0168(<2%)
The Experts… Allele frequency Allele / DNA variant A T A G G G C C T C AC ACA G C A T 0.31 A T A G G G C C T C AC ACAC A G C A T 0.32 A T A G G G C C T C AC ACAC AC A G C A T 0.14 A T A G G G C C T C AC ACAC AC AC A G C A T 0.23
Normal instability: Jumping genes
Transposable elements interrupt the chromosome and jump around