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Lecture

BIO120H1 Lecture Notes - Philippine Standard Time, Genetic Drift, Potentilla


Department
Biology
Course Code
BIO120H1
Professor
Benjamin Wright

Page:
of 5
Lecture 7
Population Differentiation and Local Adaptation
Key Concepts/ Terms:
Genetic differentiation
Geographical variation
Population
Phenotypic plasticity
Migration
Reciprocal transplant studies
Gene flow
Ecological race
1)Population differentiation: Gene flow, Geographical variation
2)Experimental studies of local adaptation: Phenotypic plasticity, Transplant studies
If there is no mating then there is no gene flow
Number One:
Populations are frequently sub-divided into smaller units based on ecological or behaviour factors. For
example, populations of fish in tide pools, trees in farmland woodlots, and insects on host plants, are sub-
divided because suitable habitats are not continuous in distribution. In fact, a continuum exists between
large populations with random mating and small sub-divided populations with localized inbreeding.
The degree to which a population can be delimited from other populations depends on the level of gene
flow between them. Gene flow and migration are similar terms. Migration can be thought of as the
movement of individuals from one population into another, whereas gene flow refers to the movement of
genes from one population into another. The degree to which gene flow takes place depends on the size of
the gaps that separate populations of a particular species, the degree to which individuals move, and the
distance over which mating can take place.
If gene flow between two populations is extensive, the two populations may become, in effect, one
panmictic (random mating) population. Thus the rate of gene flow influences the effective size of the
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population. Regular gene flow between two populations will prevent the two populations from diverging
from one another through different selection pressures or genetic drift. Thus gene flow can be a
conservative force slowing down population differentiation and evolutionary divergence and homogenizing
the genetic composition of populations.
In wide ranging species, population in different parts of the geographical range are inevitably faced with
varying ecological circumstances. Different selection pressures in different parts of a species range give
rise to genetic differentiation among populations. Genetic differentiation among populations can
also arise thought the process of genetic drift, especially in species that occur in small populations.
The study of geographical variation began with C. Darwin and A. Wallace. Many evolutionary hypotheses
are tested by examining variation patterns in living organisms. Evolutionary biologists use varying levels
of differentiation among population, races, sub-species, and species to infer the course of evolutionary
change. Observations of this type indicate that evolution is generally a gradual process with differences
among populations of a species ranging from small to large.
Microclimates- south facing slope receives more sun (can have adaptation differences)
Selection is driving those populations to be different
If there is not random mating, then genetic drift will drive them to be different
Selection and drift is driving them apart
Eventually if there is enough isolation then you will see new species
Start at 0.5
Random sampling of alleles every generation
Eventually one particular allele gets fixed or lost
If a population gets split, one population could fix Big A allele and one loses it
Population can accumulate difference just by drift
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Even here one will fix and one will get lost
Isolation by distance
Migration can happen in different ways
Recent migration
Determining gene flow
Regent of chromosome in 2 different populations
In general both populations are similar which means high gene flow
Most of the alleles in one population are seen in another, then there are total difference
In general we share more then we dont
No clear sign of a geographic barrier
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