Transcript Lesson_11_Population_Genetics

Population Genetics
Objectives
To understand and be able to use
the Hardy-Weinberg principle
The background
• There are a larger number of alleles carried
in a population as opposed to an individual
Remember:
• A population is a group of individuals of the
same species that can interbreed
• This creates a gene pool and genetic diversity
Note:
• A gene pool is the set of genetic information
carried by a population whereas a genome is
the genetic information carried by an
individual
• The amount of genetic diversity within a
population can be quantified by the
Hardy Weinberg equation
• Genetic diversity of a population can be
altered by mutation, genetic drift,
migration and selection
• In order to follow evolutionary changes
and the genetic basis of inherited
variation it is necessary to study
populations not individual mating
How do we Measure Allele and
Genotype Frequencies?
• Observe the phenotypes
• Know the mechanism of inheritance for
that trait
• Know how many different alleles for the
trait are within the population
Codominant Traits
The frequency of
heterozygous phenotype =
the frequency of the
heterozygous genotype
Now look at the blood group example
on p138
The principle is different when
one allele is recessive to the
other. The frequency of the
alleles can not be directly
determined because the
heterozygotes show the same
phenotype as homozygous
dominant
The Hardy Weinberg Equation can be
applied based on the following
assumptions
• It is a large population
• The population has random mating
• There must be no significant selection
pressures on a specific genotype
• There is no significant introduction of
new alleles into the population by
mutation or immigration
What is the Equation?
2
2
P +2pq+q =1
Where p represents the frequency
of the dominant allele and q the
frequency of the recessive allele
(Now follow through the example of cystic
fibrosis on the sheet)