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Hardy Weinberg

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Evolucion GuevaraFiore

on 8 September 2016

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Transcript of Hardy Weinberg

Today's lecture:
Hardy–Weinberg principle
Population size & genetic drift
Bottle necks
Founder effect
Gene flow
Inbreeding
1
2
3
4
Hardy–Weinberg principle
Phenotypes
p = 6/20 = 0.3
Allele fq:
p+q = 1
Probability:
R: 7/10 x 7/10 = 49/100 = 0.49
B: 3/10 x 3/10 = 9/100 = 0.09
BR: 7/10 x 3/10 = 21/100
(but RB or BR) so: + 21/100
q = 14/20 = 0.7
0.3^2
0.7^2
Genetic structure
Any pattern in the
genetic makeup
of individuals within a population.
Population
genetic structure
is the heterogeneity in allele freq among the populations caused by limited gene flow.
All populations have genetic structure, because all populations can be characterised by their
genotype or allele frequencies.
The study of population genetic structure is a fundamental problem in population biology because it helps us obtain a deeper understanding of the evolutionary process.
The distributions of individuals and the gene flow connections between different areas can be very important in evolution.
By population structure, population geneticists mean that, instead of a single, simple population,
populations are subdivided in some way.
The overall "population of populations" is often called a
metapopulation
, while the individual component populations are often called
subpopulations
or local populations or demes.
In many real populations, there may not be any obvious individual populations or substructure at all, and the populations are
continuous
.
For instance, among humans, Scotland, the North of England, and London have some quite major
language differences
, suggesting
substructure
, but you would be hard put to find an exact boundary where there is a changeover.
Such populations are structured, but continuously, in space.
However, even in effectively continuous populations, different areas can have
different gene frequencies
, because the whole metapopulation is not panmictic.
Panmixia (or panmixis) means random mating:
A panmictic population is one where all individuals are potential partners. This assumes that there are
no mating restrictions
, neither genetic nor behavioural, upon the population, and that therefore
all recombination is possible
.
A very good definition of population structure is when populations have
deviations from Hardy-Weinberg proportions
, or deviations from panmixia. If there is inbreeding, or selection, or if migration is important, then populations can be said to be
structured
in some way.
IMPORTANCE:

If populations are subdivided, they can
evolve apart,
somewhat independently. Population structure allows populations to
diversify
. This is the reason why population structure is a very important part of evolutionary genetics.
The simplest test for population structure in a sexually reproducing, diploid species, is to see
whether genotype frequencies follow Hardy-Weinberg
proportions as a function of allele frequencies
Population genetics
is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology.
Studies in this branch of biology examine such phenomena as adaptation, speciation, and
population structure.
Full transcript