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BIO120H1 Lecture Notes - Camouflage, Fetus, Light Skin

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LECTURE 7 Natural Selection
Microevolution: Evolutionary Forces
-five evolutionary forces significantly alter the genetic structure of a population
1. mutation
2. gene flow
3. genetic drift
4. nonrandom mating
5. selection
Source of new variation
Relatively rare
May be
short generation time
mutations- important source of variation
beneficial mutations can increase in frequency very quickly
-Created by binary fission
-If a mutation is beneficial it would be really quickly passed on, if they are more
beneificial they will reproduce more quickly
Gene Flow
Migration: movement of individuals from one population to another, followed by breeding
– Immigration
– Emigration
-Flow of genetic information or passing on genetic information. It is important because it
is about reproduction. It is done by immigration and emigration.
Genetic Drift
- Random change in gene frequency in small populations over time due to chance: can
occur in 3 situations:
1. Chance events
2. Bottleneck effect
3. Founder effect
Chance events – small populations are especially prone to loss of alleles though chance
-Dealing with small population sizes. When you have small population sizes what happens
with chance events bottle neck effect and founder effect
Bottle Neck Effect
Population bottleneck – genetic change resulting from a dramatic reduction of population
-You could have extinction, If you have small population size you already have a small
gene pool. If a predator takes away the only one type of gene pool then that gene will
be lost. If there is a larger population of one gene then losing one will not affect the
gene pool.
-You start with a large population, but then as you move up the population you end up
having a smaller population.
-An example of a bottle nect affect is the elephant seal.
Founder Effect
genetic differences resulting from a small number (few individuals) of breeding
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