Human Genetics. Multifactorial Traits. Genes and the Environment. Genes and the environment interact to mold many of our traits. Mendelian trait due to a single gene. Polygenic trait due to multiple genes. Multifactorial trait results from action of
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Mendelian trait due to a single gene
Polygenic trait due to multiple genes
Multifactorial trait results from action of
genes and the environment
Nature Genetics31, 235 - 236 (2002) doi:10.1038/ng0702-235
Congenital malformations traits.
Congenital dislocation of the hip
Congenital heart defects
Neural tube defects (spina bifida etc.)
Club Foot (Talipes)
Adult onset diseases
Ischaemic heart disease
SchizophreniaDiseases can be Polygenic
Five eye colors can be produced by the interaction of just two genes.
- are influenced by genes and by the environment
Many genes +
fingerprints prenatal touch
skin color sun exposure
Improved nutrition can impact height.
General Population (no affected relatives)
0.1%Empiric Risk of Cleft Lip
Additive Effects of
Useful to study
- Relatives in pedigrees
- Adopted children
- Twins raised apart
Relation understood inheritance patterns? %concordance % expected
MZ twins 0.81 1.00
DZ twins 0.42 0.5Heritability Calculation
Estimated from the proportion of people sharing a trait compared to the proportion predicted to share the trait.
Concordance - % of pairs of individuals that share the trait
(both affected or both unaffected)
Language skills (measured by vocabulary at age 2)
Adopted individuals understood inheritance patterns?
- Share environment, but not genes
- Share environment and 50% of genes
- Identical genotype, shared environment
- Twins raised apart
- Share genotype, but not environmentHow do we isolate environmental and genetic components to determine heritability?
- the expression of a trait in both twins
- measured as a percentage of pairs in which both twins express the trait.
- if both twins don’t share the trait - discordant
Bottom line: concordance values
A trait observed to be present more often in both members of a MZ twin pair than in both members of a DZ twin pair is presumed to have a significant inherited component.
Nucleotide site with more than one allele is a polymorphism.