Complex Traits Flashcards
Quantitative vs qualitative traits
Qualitative: single gene trait- either you have the disease or you don’t
Quantitative: phenotype is a continuum, multiple genes and environmental factors are involved
Threshold
Point on quantitative trait continuum past which a person is considered to have a disease
Heritability
Proportion of variation in a trait that is due to genetic variation
How to calculate heritability
H^2 = Vgenetic/ V total
Phenotype is a result of which two factors?
Genes and environment
Specificity of heritability
Heritability is specific to a given population
Can heritability change over time?
Yes- can change if environment changes
100% heritable trait (single gene disorder) can be changed by environment (drug cures disease, etc.)
Genetic architecture describes what?
How genetic variation influences a trait: number of loci/genes, their effect sizes, interaction with one another, interaction with environment, molecular basis
Genetic architecture of cystic fibrosis
Though cystic fibrosis is a Mendelian disease, genetic modifiers, alleles at other genes, have an effect on the severity
Genetic architecture of type 1 diabetes
Type 1 diabetes is a complex disease, but a major gene in MHC complex is the most significant association for the disease (autoimmune disorder)
Many additional loci in the genome play a role
Genetic architecture of human height
Height is a classic quantitative trait: polygenic Involves many loci, each one having small effects Extreme phenotypes (very tall or very short) result from many alleles with effects in the same direction coming together
Genetic architecture of heart disease
Presence of Mendelian alleles in rare families (ex- mutation in LDL receptor reduces uptake of LDL in liver, increasing circulating cholesterol)
In most cases, many common variants of small effect
Genetic architecture of cognitive traits
Very complex architecture
Many variants of very small effect
