Lecture 2 - Hardy Weinberg Equation Flashcards
What is Population Genetics
It is the understanding what evolutionary forces are at play that drive changes in allele and genotype frequencies
What is the use of population Genetics
Fundamental to interpreting evolutionary history and understanding evolutionary forces
Also has practical applications to human genetics, animal/plant breeding and conservation
allele
Genetic variants of a gene
Genotype
The allelic composition of a gene, set of genes or even the whole genome
Phenotype
The physical realisation of the genotype
Gamete
Haploid product of meiosis in sex cells
Zygote
diploid product of fertilisation
Homozygote
Same allele at a locus
Heterozygote
different allele at each locus
Gene pool
the sum of alleles at all loci in a population
Affect of gene pool on the next generation
The next generation is made up of a random selection of genes from the gene pool
How is the gene pool an idealized concept
Unlikely that genes for the next generation are selected at random
For example it is more likely that an animal will mate with an individual in the same herd
Polymorphism
More than one allele present at a single locus within a population of organisms
What is the zero-force law of population genetics?
Hardy Weinberg equation
How is the Hardy Weinberg equation a zero-force law?
As it measures what happens when there are no pressures on a population
What is the hardy weinberg equation an application of?
An application of mendels laws on populations rather than individuals
What is the Hardy-Weinberg equation?
p^2+2pq+q^2=1
p= the frequency of allele A
q= the frequency of allele of A1
where p>=0, q<=1 and p+q=1
What are the assumptions of the hardy weinberg principle?
No mutations
No migration
Mating is Random
Population size is infinite
No natural selection
Eggs and milt bucket experiment
A bucket of sperm and eggs
Can be studied as it is a real-life gene pool with random mating
What does genotype frequencies depend upon?
Underlying allele frequency
Hardy Weinberg Equilibrium
Principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors
How to test for deviation from HWE
Compare the observed genotype frequencies and expected genotype frequencies
Then do an x-square test
How can HWE be used to predict frequencies in gene carriers?
Most genes causing disease are recessive/dominant alleles which means that you cannot detect heterozygotes from homozygote dominant individuals
However if you use the HWE you know that the homozygote is q^2 and therefore can work out the frequencies of the other alleles and genotypes
Importance of HWE
Proof that in absence of any evolutionary forces allele and genotype frequencies remain constant over time
Explains why genotype frequencies rarely deviate from HWE expectations
Can be used to predict frequency of disease carriers
Example of a basic population genetics model
Null hypothesis that can be rejected and prove that evolution occurs
