Mitochondrial DNA haplotype of dunlin

1
2 Population genetics
break
2
Two subpopulations
A p0
A p1
a q1
a q0
In such a case, there are no heterozygous
individuals in the population, although according
to HW, there should be. There is a deficit in
heterozygous. Is this phenomenon general?
3
Two subpopulations
Subpopulation 2
Subpopulation 1
A p1
A p2
a q1
a q2
We assume panmixia (random mating) in each
subpopulation.
4
Two subpopulations
Subpopulation 2
Subpopulation 1
A p1
A p2
a q1
a q2
We assume N1 individuals in population 1, N2
individuals in population 2. Let NN1N2. Let K1
be the fraction of population 1 out of the entire
population K1 N1/N. K2 1-K1.
5
Two subpopulations
Subpopulation 2
Subpopulation 1
A p1
A p2
a q1
a q2
What is the general heterozygosity in
subpopulation 1?
This is also the HW heterozygosity, which is
expected since the subpopulation is in panmixia
6
Two subpopulations
Subpopulation 2
Subpopulation 1
A p1
A p2
a q1
a q2
What is the expected heterozygosity, under HW in
the entire population? To compute this we first
have to compute the frequency of A and a in the
entire population. Then
7
Two subpopulations
The frequency of allele A in the entire
population is
8
Two subpopulations
The expected heterozigosity under HW is often
also called Hexp
9
Two subpopulations
Hexp is the probability to sample a heterozygous
if one first mix all the alleles of the entire
population. The question is what is the
different between this expectation and the actual
frequency of heterozygous in a sample from the
population.
10
Two subpopulations
Hexp is the probability to sample a heterozygous
if one first mix all the alleles of the entire
population. The question is what is the
different between this expectation and the actual
frequency of heterozygous in a sample from the
population.
11
Two subpopulations
A p1
A p2
a q2
a q1
K
1-K
Probability to sample a heterozygous individual
in subpopulation 1
Probability to sample subpopulation 1
12
Two subpopulations
A p1
A p2
a q2
a q1
K
1-K
We will show that Hobs is always smaller than
Hexp and that this is a general phenomenon for
subpopulations.
13
Heterozygote deficit
F (Hexp-Hobs)/Hexp
Heterozygote deficit (also known as Inbreeding
coefficient) F measures the fractional reduction
in heterozygosity relative to random mating
14
Rewriting F
15
Rewriting F
16
Simplifying terms
F is always non negative -gt reduction in
heterozygosity relative to random mating is a
general phenomenon when there is non random
mating.
17
Heterozygote deficit
A p1
A p2
a q2
a q1
K
1-K
Fgt0 we have a heterozygote deficit F0 when
p1p2 (or K0). F varies depending on the locus
considered
18
Heterozygote deficit
p1
Pn
p4
p3
p2

The above argument for two subpopulations also
holds true for more than two subpopulations
19
Wahlund effect
This reduction is called the Wahlund effect
20
2 Population genetics
break
21
Other mechanisms that can cause a heterozygote
deficit in a population
Non random mating (no panmixia) 1. Autogamy
autofecondation 2. Positive assortative mating
sexually reproducing organisms that tend to mate
with individuals that are like themselves in some
respect.
22
Autogamy Cleistogamy flowers
Cleistogamy the character closed flowers,
which is directly linked to self-pollination. All
the genes in the individual will slowly loose
genetic diversity.
23
Positive assortative mating
Animals that choose partners with a specific
character as they have (e.g., a fly with red eye
will prefer to mate with a fly with red eye).
Not all the genes will loose genetic diversity
to the same extent. The genes responsible for the
selected type of segregation will be most
homozygous.
24
Excess of heterozygote
Negative assortative mating sexually
reproducing organisms tend to mate with
individuals that are different from themselves in
some respect. Advantage of the rare individual
with rare genotypes will reproduce more.
25
Negative assortative mating an example
The Sporophytic (the diploid form of plants)
Self-Incompatibility (SSI)
The female part of a plant
26
Advantage of the rare
In some mating systems a male bearing a rare
allele will have a mating advantage. Rare allele
advantage will tend to increase the frequency of
the rare allele and hence increase
heterozygosity. This is also true for the human
population.