Multifactorial Flashcards
difference between single gene and multifactorial gene
single - determined by alleles at a single locus (ex: AR, AD, X linked diseases)
multifactorial/complex - genes + environment
amount of diseases in the human population that can be attributed to multifactorial disorders
a hell of a lot
explains disorders that do not show clear Mendelian inheritance but show familial aggregation
multifactorial inheritance
what does it mean for multifactorial disorder to show quantitative trait
number of contributing (dominant) alleles determines phenotype not the specific combination (so can be additive [AA] or non-additive [aa])
mutations or variations in more than one gene contribute to the trait describes?
polygenic
environmental factors that can influences diseases
diet, environmental toxins, lifestyle
polygenic theory of quantitative traits shows what type of expression/curve
normal or gaussian distribution (so a range/variations in phenotypes)
frequency if only controlled by one gene
frequency if controlled by two genes (digenic)
1 gene: 1, 2, 1
2 genes : 1, 4, 6, 4, 1
what happens to phenotype if controlled by more than one gene
broader range of phenotype/continuous phenotype
human characteristics controlled by polygenic/quantitative traits (does not exclude that there are environmental factors)
height, weight, skin color, intelligence etc
Say intelligence is a polygenic trait (which it is) and controlled by only two genes (which it is not). Two alleles exist at each locus, one fully additive (A and B) and one non-additive (a and b). How smart are you if your mother is A/A B/B and your father is a/a B/B?
intermediate between mother and father
all factors that contribute to a disease and the type of graph it produces
liability
normal/gaussian distribution
point where there is enough contribution to some underlying quantitative variable to cause expression of abnormal phenotype
threshold
does where you sit in a gaussian distribution a result of your genes and environment
yeah
what happens to the distribution curve in families with “bad genes” and what does that mean
curve shifts to the right meaning more people are above the threshold
definition: the more closely related you are to someone with a complex disease, the more likely you are to have some of the same alleles
familial relative risk
what happens to your risk of getting a disease for every degree distance you are away from affected persons
it decreases by 1/2 with every degree
1/2 (sibs and parentals) –> 1/4 (grandparents, uncles) –> 1/8 (first cousins, great grand parents)
equation for relative risk ratio
lambda = prevalence of disease in relatives of affected person / prevalence of disease in general population
what does it mean to have a lambda of 1
relative is no more likely to develop the disease than any other individual in the general population so basically no genetic influence
what does sit mean to have a large lambda or a low lambda
large lambda - greater familial aggregation
low lambda - less likely familial aggregation and more likely greater impact of environment and multiple genes
is the risk of recurrence lower or higher in relatives of severely affected individuals
higher
what does it mean if multiple members in the family are affected with the same multifactorial inheritance disease
genes contribute greatly to the disease so higher lambda and greater risk of having disease if part of this family
pyloric stenosis is more common in what population
males (have a lower liability threshold)
what happens to recurrence risk if the less likely affected sex is the one with the disease
then there is a greater recurrence risk of the disease …and even greater for the more susceptible sex
