Heritability Flashcards
Discrete Traits (Definition and list two examples)
Traits in which only one or a couple of genes determine the trait. An example is eye color and pea plant texture (wrinkled or smooth). Usually have two alleles determining trait within the gene.
Continuous Traits
Traits determined by numerous genes (and thus numerous alleles). Example include height, hair color, obesity
What two components make up the phenotype of an individual?
Genes and enviroment
Polygenic Traits
Traits determined by more than one gene (usually continuous)
What causes continuous variation?
The combination of the effects of genes and environment
In which case is it easier to predict genotype from phenotype in terms of genes and the environment?
Easiest to predict when environment is having very little effect on expression of the genes
Vp
Total phenotype variation
Vg
Variation from differences in genetic factors
Ve
Variation from environment
VgXe
Variation due to the interaction between genes and environment
Heritability Equations
Vp=Vg+Ve+Vgxe
h^2=Vg/Vp
Heritability in own words:
The genetic variation in a population accounted for by genes
What tests is used to discover heritability?
An ANOVA to compare differences in variation and regression to compare parents to offspring
How are regression lines used in twin studies?
To compare a trait in one twin to a trait in the other twin and analyze the slope
What does rMZA represent?
The correlation coefficient of a certain trait among monozygotic twins
Correlation equation for rMZA?
=Vg+Ves/ Vt
What is special about Ves in the correlation equation?
It is negligible because the twins are said to be reared in different locations with different enviroments
What does the Ves negligible assumption lead to?
Overestimate in heritability because although twins weren’t reared together, they may have shared similar enviroments
4 Criticisms of Twin Studies
1) Ignored shared environment in identical twins or unshared environment in twins raised together
2) Mono-zygotic twins not genetically identical
3) Twins are NOT a random sample of population
4) Twins could seek out same niche based on SMALL number of genetic similarities
What is the misassumption regarding what heritability measures?
Not a measure of genetic control within an individual, but the extent to which genetic differences among individuals within the population influence the trait
Genome Wide Association Study
Measures the association between SNP’s in population and phenotype and looks at the function of genes associated with those SNPS determining phenotype
What is the reason for missing heritability in the GWAS?
We do not have the entire genome for each patient so some of the variation is not captured in the SNP’s
What kind of SNP’s will you have if you have a common disease with a common variant?
Many small effect SNP’s
