Topic 5 : Mendelian Genetics in Populations 1: Selection and mutation

What can evolve and not

Only populations evolve, not individuals

What is population genetics?

Integrates theory of evolution wirth mendelian genetics

How do we determine genotypes?

By looking at the phenotype- Intestinal schistosomiasis example and examining the different proteins encoded by the alleles

How does protein help us look for genetic variation?

The different allels will make different versions of preoteins because theyèll have differences in amino acids which causes different folds and shapes to occur

What was the first method to determine genotypes

Protein electrophoresis and measure the diversity in locus- because different alleles would give different shapes and they would all be placed at different spots due to their weight. If het then 2 is supposed to come out in one lane, if not then homo

How much is an individual heterozygous at their genes?

33-50%

How many of the genes that code for enzymes are polymorphic?

4-15%

What is polymorphic

-more than 1 allele in the POPULATION!!

How to measure genetic variation?

1. Find genotypic variation → Look at phenotypes

2. Look at proteins that are made from the different alleles

   1. Use genetic techniques to find out the alleles: PCR, Microsatellite gel and electrophoresis

How to read microsatellite gel

each well should show two distinct bands or 1 thick band representing the alleles, can determine if homo or hetero

Genetic variation - Calculate allele frequencies

For allele frequencies, count the total popn and multiply it by two and homo x 2 and hetero x1 —> divide by popn x two

Hardy weinberg Assumptions

1. No mutation

2. No selection

3. Individuals mate at random

4. no genetic drift

5. no gene flow

What is hardy weinberg a model of?

Model of a population, not an individual

-only works for diploid organisms

What is panmictic

random mating

Genotype frequencies in panmictic populations

In panmictic populations —> Genotype frequencies DO NOT change because each male mates with a random female who likely has the same genotype frequencies —> because the whole population has the same frequency

gametes in panmictic population

Gametes are proportional to each other in the population and different alleles should equal to 1

Is evolution occuring under H-W? (2)

1. Genotype frequencies can be predicted from allele frequencies

2. Alleles frequencies are stable over a long period of time

—> If these two are true then evolution doesn’t occur

Under HW, what are the ratios of genotype frequencies for 2 alleles

homozygous are squared - p² and q²

Heterozygous - pq + pq = 2pq (heteros can happen 2 ways)

HW equation

p² +2pq +q²

What happens when actual vs expected values are similar or the same

Then assumption 1: Popn is not evolving is not violated and population is in hardy weinberg eqm

What is heterozygosity

heterozygous /sample pop

Heterozygote deficity

Actual heterozygote population is less than the expected

what does large population mean in HW

Genetic Drift —> when this assumption is violated then population is small and genetic drift occurs

What varies in fitness genotypes or phenotypes?

Genotypes: they give rise to phenotypes that allow individuals to be fit or not

Fruit flies selction example

Control group: Fruit flies-have genes to breakdown ethanol → ethanol breakdown fixation.

What happens when selection is symmetrical

genotype frequencies change but allele frequencies do not

When is selection rapid /slow

what is heterozygotes advantage

WHat are the patterns of selection (5)

1. Heterozygote advantage -: being het is more advantageous than being homo

2. Heterozygote inferiority: being homozygote is more advantageous than being het

3. Selection is rapid: recessive allele is lethal and common

4. Selection is slow: recessive alleles are lethal and rare

5. Frequency dependent selection

Elderflower orchids example

Bees will fly to rare flowers to search for nectar and go in a 1:1 ratio between diff coloured flowers. This is negative frequency dependent selection

What is the source of new alleles in a population?

Mutations

Imagine a mutation happens in a population wheere allele A turns into a at a rate of 1 in 1000. Initial frequncies of the alleles are : A: 0.9 and a : 0.1 . what is the new allele freqiencies

what can change allele frewucnies over a long period of time?

mutations

Drosophila and salt mutation experiment

inbred solution w same gene variations: Control group no salt: survived but also had mutation to be able to breakdown salt, group w stressed line: mutation to stop breakdown of salt increased a LOTTTTT due to environment and selection pressure

How can deleterious alleles persist (2)

1. mutation of the recessive allele

2. Heterozygote advantage

what is mutation selection balance

rate of mutation of recessive allele = rate of getting them out of the population