Are most diseases Mendelian in nature?
No, most have multifactorial inheritances
What are the Mode of Inheritance of Multifactorial traits?
Familial clustering but without obvious family pattern
The recurrence risk is higher the more family members that are affected
Describe a Normal Distribution curve is regard to frequency of alleles
Many people a relatively "normal" # of harmful alleles
Few have no harmful, all protective
Few have all harmful (have disease)
What is a classic example of a quantitative trait?
Height! Large number of alleles that affect height
But environment is also incredibly important
Describe the "threshold model"
Ex. More than 9 predisposing alleles is enough to cross threshold to disease
Individuals w/ less than 9 predisposing alleles are (usually) not affected
Environmental factors muddy this up
Average risk for normal parents of one affected child having another?
The more children with a multifactorial disorder, _________ the recurrence risk...
Is it possible to have multi-factorial diseases affect different sexes with different frequencies?
Yes! In these disorders, the most likely individual to be affected is the most susceptible sex offspring of the least susceptible sex parent
Thershold may be different in different sexes
Proportion of the phenotypic variance caused by additive genetic variance
Reflected by the degree of resemblance between relatives
Estimate of the degree to which relatives will resemble one another
Identical twin studies useful here
Used to determine mutlifactorial inheritance
Combines varying factors (prior, conditional, joint, posterior) to determine % of being a carrier