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Lecture 2:Haplotypes:
- Many higher organisms are diploid, they carry 2 haplotypes. One from the mother and one
from the father. So the haplotype is the DNA that you get from one parent so from your
father or from your mother.
Haplotypes as a measure of diversity:
- The number of haplotypes is not a good diversity measure, because it depends on:
o Length
o Sample size
Only fraction of possible haplotypes (2S) is observed
S = length of the haplotypes in bp
o Recombination generates new haplotypes
But you don’t really get new variation
Genotype-phenotype relationship
- Simple mendelian traits are the exception, not the rule.
- Complex relationship, not 1:1
o Single traits influenced by many genes
Human height >1000
o Pleiotropy:
Single gene affects more than one trait
o Epistasis:
Interactions between genes
o Environmental influences
- So these relationships are complex.
1.3 the causes and maintenance of variability:
- we see a lot of genetic variation
Hardy-Weinberg equilibrium:
- What happens when no forces act on the population?
o No selection
o No mutation
o No migration
o No random events ( large population)
o Random mating of parents
- Hardy-Weinberg Law:
o Allele and genotype frequencies remain constant
, o Variability is maintained for ever
o Serves as a null-hypothesis / null-model.
When it kind of holds it can be used as starting material to work further from
there.
Is this population in Hardy-Weinberg equilibrium:
- One locus, 2 alleles A and B
- 100 individuals
o 36 AA
o 28 AB
o 36BB
- Is this population in Hardy-Weinberg equilibrium
The hardy-Weinberg Law:
- Consider a locus with 2 alleles: A and B
- Frequency of A = p
- Frequency of B = q
- P+q=1
- fAA = p2
- fAB = 2pq
- fBB = q2
- The genotype frequencies follow from the allele frequencies
- Beware: p2 + 2pq + q2 = 1 is always true, and has nothing to do with HWE
Genotypes frequencies are determined by the allele frequencies, and do not change over a
generation.
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