Lecture 10 - Population and Quantitative Genetics

What is Population genetics?

moving from looking at a few organisms to allele and genotype frequencies in whole populations

What is the focus of population genetics?

• genotype and allele frequencies

• change in genotype and allele frequencies overtime

• population to population variation (ie. variation between populations in genotype and allele frequencies) → the fact that when you go from one population to another you find the frequencies of these things differ

What are changes in population level variation due to?

• mutation

• migration

• natural selection

• genetic drift

What were the 3 examples of population genetics given?

• Frequency of blood type B across a geographical region → shows the frequency of type B blood as you move across Europe → higher percentage in the east reflecting a pattern of migration overtime

• Frequency of an allele in flies overtime → a allele frequency changes over time due to an experiment putting flies in bottles and giving them different diets → those exposed to ethanol had higher frequencies of a specific allele

• the frequency of a hemoglobin allele associated with sickle cell anemia → with two copies of the allele the person with have the disease → frequency is high at equatorial regions of the world

Explain the method for analyzing one of the two homologous chromosomes in humans?

• the example of tool given is sequence level variation

• the individuals being studied are called haplotypes because they are a set of closely linked DNA variations (alleles or SNPs) on a single chromosome

• some of the base pairs vary due to SNP

• the astrics show where individuals vary

• there can also be an absence of base pairs due to an insertion or deletion

• there can also be repeats of a few nucleotides called micro satellite variation

• # single locus polymorphisms → look at columns

• # different haplotypes → look at rows

What are the benefits of these molecular tools?

• cheep

• effective

• very informative

• not restricted to looking at single allele at a time → capable of looking a t the whole genome over time and space

What is genetics at the population level?

1. concentrates on collections of individuals and their genetic properties, especially frequencies of alleles, SNP’s, genotypes, haplotypes in time and space (geography, habitats)

2. studies the origin, maintenance and change of allelic and genotypic variation in populations

3. make use of models to study the processes that influence population genetic composition and make predictions about how it will change

What is the gene pool model?

a set of individuals showing a pool of alleles

no population behaves the way we want it to but its close

• all plants and animals have some kind of boundary (ie. pollen doesn’t go everywhere which places a boundary, animals also mate close to home → they don’t go very far to look for a mate)

What is the notation for genotype frequencies?

for a gene with 2 alleles:

• f(AA), f(Aa), f(aa)

• sum must equal to 1

frequency can be calculated by taking the number of genotypes of that allele and dividing it by the total genotypes

How are allele frequencies calculated and what is notation?

for a gene with 2 alleles, A and a:

frequency of A is denoted p

frequency of a is denoted q

p + q = 1

• you can either count all the letters individually and divide by the total

• p = f(AA) + ½ f(Aa)

• q = f(aa) + ½ (Aa)

can you calculate genotype frequencies in the next generation if we know the frequencies of the previous generation?

we can only do this if there is random mating, no mutation, no selection, no migration and no drift

What is this idea of not evolutionary forces acting on the population?

Hardy-Weinberg proportions

f(AA) = p²

f(Aa) = 2pq

f(aa) = p²