LECTURE #9 : Gene Flow

TEXT : Hedrick, Chapter 5

Populations are often subdivided into smaller units, due to ecological factors (geographical structured, etc.) or behavioral factors (social structure, etc.)

Definition of Gene Flow - Genetically effective migration among subgroups

Migration = immigration and emigration

Assumption: Genetic exchange results from the movement of individuals (as opposed to dispersal)

Change in allelic freqency, dependant upon the rate of migration

(i.e. allelic frequencies could change fairly quickly, given a high rate of migration of a new allele.)

What is it?

a simple model of population structure to evaluate the potential effect of gene flow on genetic variation.

gene flow into a single population from an outside source (unidirectional)

m = rate of migrants moving to island each generation

1-m = proportion of residents each generation

WHAT HAPPENS?

if m = 0, then q = q_m, and there will be no change in allelic frequency (this would be a condition where no gene flow was occurring)

if q< q_m, then the frequency of the allele will increase

if q> q_m, then the frequency of the allele will decrease

A model in which gene flow occurs among subpopulations

m11 = proportion of residents each generation

m12 = rate of migrants moving from q1 to q2 each generation

m21 = rate of migrants moving from q2 to q1 each generation

etc.

Example of a population which fits the general model of gene flow:

here, if q1 were the Nuer, q2 the Dinka, and q3 the Shiluk,

then

m11 = .9850 = proportion of residents each generation

m12 = .0138 = rate of migrants moving from q1 to q2 each generation

m21 = .0125 = rate of migrants moving from q2 to q1 each generation

Any number of groupings of populations are possible. These divided populations are called SUBPOPULATIONS

When subpopulations exchange gene flow, the subpopulations are considered together as one population, also known as a METAPOPULATION

Some examples: