lecture 17 edited

Complex trait

A phenotype influenced by multiple genes AND environmental factors, showing continuous variation rather than discrete categories

Polygenic trait

A trait controlled by many genes each contributing a small effect to the overall phenotype

Single gene trait

A trait controlled by one gene that follows Mendelian inheritance and shows discrete phenotypic categories such as affected or unaffected

Continuous variation

The bell curve distribution of phenotypes seen in polygenic and complex traits with no sharp boundaries between categories

Discrete variation

The pattern seen in single gene Mendelian traits where individuals fall into distinct phenotypic categories with no intermediate forms

Regression to the mean

The tendency for offspring of extreme individuals to have phenotypes closer to the population average rather than more extreme

Bell curve distribution

The normal distribution shape seen in complex traits where most individuals cluster near the average and fewer appear at the extremes

Environmental effects on height

Factors including prenatal nutrition, childhood nutrition, illnesses, endocrine function, injury, medical treatments, and age that influence how tall a person grows

Genetic effects on height

Contributions from genes including growth hormone and its receptor, Noonan syndrome genes, Turner syndrome genes, Laron syndrome genes, vitamin D receptors, and at least 24 other genes with unknown functions

Mean

The average value of a phenotype in a population; the center of a bell curve

Variance

A statistical measure describing the spread or variability of phenotypes around the mean in a population

Heritability

A population statistic scored 0 to 1 describing what proportion of the variance in a phenotype can be attributed to genetic differences among individuals in that population

Heritability misinterpretation

The incorrect assumption that a heritability score predicts how much of an individual's trait is due to their own genes; heritability only describes population level variance

Heritability varies by population

The concept that a heritability score calculated in one population cannot be applied to a different population because gene frequencies and environmental conditions differ

Concordance

The proportion of twin pairs in which both twins share the same phenotype; used to measure genetic vs. environmental contributions to a trait

Monozygotic twins

Identical twins arising from one fertilized egg that splits; share essentially 100% of their genes and the same prenatal environment

Dizygotic twins

Fraternal twins arising from two separate fertilized eggs; share approximately 50% of their genes and the same prenatal environment

Twin concordance study

A research method comparing concordance rates between identical and fraternal twins to estimate the genetic contribution to a complex trait

Fully genetic trait twin study result

Produces near 100% concordance in identical twins and significantly lower concordance in fraternal twins such as ABO blood type with identical twins at 100% and fraternal twins at 66%

Fully environmental trait twin study result

Produces similar concordance scores in both identical and fraternal twins because genetics plays little to no role such as tattoos where identical twins score 34% and fraternal twins score 38%

Gene and environment trait twin study result

Produces higher concordance in identical than fraternal twins but the identical twin score is well below 100%, indicating both genetic and environmental influences such as cleft palate with identical twins at 40% and fraternal twins at 3 to 6%

Cleft palate concordance

Identical twins show 40% concordance and fraternal twins show 3 to 6% concordance, indicating a significant genetic component alongside environmental influence

Autism concordance

Identical twins show 90% concordance and fraternal twins show 4.5% concordance, indicating a very strong genetic component

Acne concordance

Both identical and fraternal twins show 14% concordance, indicating the trait is primarily environmentally determined

Hypertension concordance

Identical twins show 62% concordance and fraternal twins show 48% concordance, indicating both genetic and environmental contributions

Obesity twin study conclusion

Identical twins show consistently higher concordance than fraternal twins across all BMI thresholds, indicating a significant genetic component to obesity; the gap widens with age

LDLR gene

The gene encoding the low density lipoprotein receptor; loss of function alleles follow an autosomal recessive pattern and dramatically increase risk of early heart attacks; one of the most influential single genes affecting cardiovascular risk

Cardiovascular disease uncontrollable risk factors

Age, male sex, specific genes, homocysteine metabolism, and leukocyte adhesion

Cardiovascular disease controllable risk factors

Fatty diet, hypertension, smoking, high serum cholesterol, stress, diabetes, and lack of exercise

GWAS

Genome wide association studies; a method used to scan entire genomes across many individuals to identify candidate genes that each contribute a small amount to a complex trait

Pharmacogenetics

The field of testing individuals for genetic variants that affect how they metabolize drugs, enabling personalized medicine rather than population level prescribing

BiDil

A heart failure drug approved in 2005 for self identified Black patients; illustrates the danger of applying population level data to individuals since race is not genetic and individual drug response depends on personal genetic variants

Race and genetics

Race is not a genetic category; there is more genetic variation within racial groups than between them, and no genetic markers 100% accurately predict race

Population data limitation

Statistics describing populations such as heritability and mean group differences cannot be used to make predictions about specific individuals within that population

Height heritability

Approximately 76 to 90% of variation in height within a population is attributable to genetic differences depending on the population studied; this does not mean any individual's height is 80% determined by their genes