Population and Quantitative Genetics Flashcards
How would you work out genotypic frequency?
- no. of individuals with genotype / total no. of individuals
What is the Hardy Weinberg Model and what are the assumptions of it?
Genotypic/allele frequencies will remain same after single generations of random mating following assumptions:
- large population
- random mating
- no mutations
- no migration or immigration
- no selection
Why is the HWM often wrong?
Non random mating can occur - (3 types)
1) Positive assortative mating - similar individuals mate with similar individuals
2) Neg assortative mating - diff with each other
3) Inbreeding - relatives with each other
What are the issues associated with inbreeding?
- reduced fitness
- increases homozygosity
What are the causes of change in allele frequency?
1) Genetic drift - random changes in allele frequency ( error = 1/2N) - Bottleneck is an example of this: Drastic reduction in pop size, new pop isn’t representative of old one. Founder effects too.
2) Natural Selection - diff genotypes have diff fitness, leads to changes in allele freq as favours certain alleles
3) Migration - movement of alleles from one pop to another. Reduces genetic differences between populations.
What is fitness?
A measure of the average contribution to the next generation
What is overdominance?
Heterozygote has highest fitness, neither allele favoured.
- selection maintains both alleles
What is a meristic (countable) trait?
- determined by multiple genetic and environmental factors and measured in whole numbers eg. animal litter size
What is Threshold traits?
- measured by presence or absence
- e.g susceptibility to disease
Definition of Phenotypic variance
- total amount of variation among individuals in some trait, caused by underlying components of variation.
Definition of Broad sense Heritability
- proportion of phenotypic variation attributable to genetic differences between individuals
- H2 = Vg / Vp
Definition of Narrow sense Heritability
- proportion of phenotypic variation that contributes to the resemblance between parent and offspring (additive genetic variance)
- H2 = AGV / Phenotypic V
- measured by regulation
- linear relationship between parent and offspring
What are the components of Phenotypic variation?
- Genetic Variance ( VG)
- Environmental Variance ( VE)
- Genotypic-environmental interaction variance (VGE)
VP = VG + VE + VGE
What are the components of Genetic variation?
Heritable Variation - additive genetic variance ( VA)
Non heritable variation -
1) Dominance genetic variance (VD)
2) Gene interaction (epistatic) - VI
What is regression?
- predicting the value of one variable if the value of other is given
What is regression coefficient?
- represents the slope of the regression line, indicating how much one value changes on average per increase in the value of another variable.
- flat line = zero heritability
What is linkage disequilibrium?
- 2 loci A and B with alleles A/a and B/b
- and Linkage EQ combos of alleles at A and B should be randomly assorted.
- LINKAGE DISEQ occurs when there’s an association with alleles at diff loci. EG A found with B
- coupling of A and B and a and b
- repulsion of A and b and B and a
What removes linkage diseq?
- recombination
What is pleiotropy?
- traits usually inherited together, a single locus / gene that affects the expression of multiple traits.
What is Quantitative Trait Locis?
- location of the genome that causes diff values of the trait in question
- tests done using genetic markers
What is the genome wide association?
- identifies casual loci by testing whether groups with diff phenotypes have diff frequencies of alleles at locus
- using a dense sequence data but also marker data
What is additive genetic variance?
- predicts resemblance between parents and offspring
What are breeding values?
- twice mean deviation of its progeny from the population mean phenotype
What is biological evolution?
- genetic changes in a group of organisms
What is Anagenesis?
- evolution taking place in a single group with the passing of time
What is Cladogenesis?
- Splitting of one lineage into two, 2 new species arise.
What is the phenetic species concept towards what a species is?
- Individuals or populations highly clustered in phenotype space - assign species boundaries from this
What is the biological species concept towards what a species is?
- gene flow between populations - assign species boundaries
What is the Phylogenetic species concept towards what a species is?
- species represent smallest set of organisms that share a common ancestor, can be distinguished from other such sets.
What is Phylogeny?
- representation of relationship between groups of organisms (lineages, populations or species)
What are Rooted and Unrooted trees? (not actual roots in the ground)
- rooted use a distantly related species to infer ancestral state ( an outgroup )
- unrooted don’t have an outgroup, we know relationship between lineages but no ancestral relationship
What is allopatric speciation?
caused by geographic isolation - no gene flow between two pops
What is peripatric speciation?
when population peripheral to a main population
What is parapatric speciation?
when populations aren’t isolated but adjoining - individuals mate locally
What is sympatric speciation?
when populations overlap forming new species in middle
2 Types of reproductive isolation
Prezygotic - don’t encounter each other, habitat isolation, temperal, behavioural, gametic incompatibility which stops a zygote forming
Post zygotic - zygote dies, f1 hybrid inviable. f2 survive but sterile
What is secondary contact?
- lineages split but come back into contact, will the hybrids be viable?
What are genetic markers?
- they feature in the genome and allow us to differentiate between diff alleles
What is forensic genetics?
match DNA samples to individual, family or species
The word ‘haplotype’ means…
refers to a chromosome block inherited as a single unit
Complex traits are…
Typically affected by many genetic and environmental factors
Correlations between traits can be due to…
- Pleiotropy
- Linkage disequilibrium
- Environmental effects
What can increase variation between populations?
1) Mutation
2) Genetic drift
3) Natural selection
Genetic markers are…
molecular variants used to differentiate between alleles
