Quantitative Genetics Flashcards
What is quantitative genetics?
genetic traits that vary continuously
weight
height
traits controlled by effects of multiple genes and allele
what are the 3 types of polygenic trait?
metric
- continuous scale, no categories
meristic
- discrete scale, counts
threshold
- present ot absent
- need to meet the threshold
What are metric traits?
mean = centre of the phenotypic distribution
study of continuously measured traits and their mechanisms
what is population variance?
average squared deviation from the mean is called the variance
What are meristic traits?
countable structures
What are threshold traits?
discrete phenotypes that are multifunctional
e.g. alcoholism, cancer, diabetes
only if reach threshold then you are considered
important in medicine?
complex disorders caused by multiple genetic and environmental factors
understanding genetic vs environmental causes
- prevention
- genetic counselling
- genetically tailored treatments
important in agriculture?
basis of selective breeding
environmental variation reduces efficiency of selection
important in conservation?
of endangered species
of captive breeding programmes
consequences of inbreeding and outcrossing
what is the phenotype?
genotype + environment
affected by multiple genes
what is variation in a population related to?
phenotypic variance = genetic variance + environmental variance + gene&environment variance
what is genetic variance?
contribution to phenotypic variation due to set of alleles present in a population and their interactions
what is environmental variance?
contribution to phenotype variation caused by differences in environmental conditions
what is broad sense heritability?
measures the importance of genetic variation relative to total variation in the phenotype
what is narrow sense heritability?
measures the importance of additive variation or variation doe to the allele present in the population, relative to total variation in causing variation in the phenotype
what is h2?
estimates vary substantially across traits, environments and different populations
used to predict change in population means under selection
when it increases, response to selection increases
how is heritability measured?
equation of straight-line graph, shows how related the two traits are
y = mx +c
How do you estimate adaptive genetic traits?
infinitesimal model
assumes infinite number of unlinked loci, each with infinitesimal effect
infinite number of genes controlling a phenotypic trait each with a very small effect
what does the population genetic theory state?
frequencies of alleles and genotypes in a population remain constant unless acted upon by non-mendillian processes
equilibrium = no evolution
what is p in hardy Weinberg?
p = frequency of one allele in the population
(study 2 alleles in locus)
what is q in hardy Weinberg?
frequency of the other allele in population
What is the hardy Weinberg equation?
p2 + 2pq + q2 = 1
p2 = proportion of population that is homozygous for first allele
2pq= proportion of population that is heterozygous
q2= proportion of population that is homozygous for second allele
When does hardy-weinberg apply?
when organisms are diploid
allele frequencies same in each sex
mendelian segregation occurs
mating occurs at random
population size is large so no genetic drift
no gene flow
no mutation
no selection
- population size so large so no genetic drift
mainly affects smaller populations
drift = allele frequency change
reduces genetic variation
- no migration or gene flow
migration transfers individuals amongst populations
gene flow transfers alleles amongst populations, increase or decrease
- no mutation
mutations increase variation
- no selection
biases which genotypes transmitted to next generation
increase or decrease variation
operate many different ways
What is linkage disequilibrium?
non-random association between two polymorphic loci
