6 Multifactorial Flashcards
what is multifactorial inheritance?
combined contribution of genes and environmental factors in the causation of a particular disease or trait
what is a quantitative trait?
- something that can be measured on a scale
- results from the additive effect of multiple genes and environmental factors
- not a yes/no situation
- height is a primary example
what is a threshold trait?
-something is either present or absent, not a gradient
what is liability?
total combined genetic and environmental factors that influence the development of a multifactorial disorder or trait
can liability be measured?
no, it is determined by the incidence of the disease in a group, using statistics of the normal distribution
liability may differ between genders? T/F
True
recurrence risk is more or less clear in multifactorial traits
less
if the proband is more sever, this means there is a greater or lesser RR?
greter
more family members having the disease does what to the RR?
goes up
in more distantly related relatives, what happens to RR?
drastically goes down
what happens to the RR if the proband is of the less commonly effected sex
goes up
what is the RR for first degree relatives in multifactorial inheritance?
approximately the square root of the population incidence
in general, what is the RR for most isolated birth defects?
approximately 4%
-however, if it is part of an underlying genetic syndrome then the RR could be much higher
how would you study if a trait is due to genes, the environment, or both?
-estimate heritability: how much of the phenotype is based on genetics
where does evidence of genetic contribution to a disorder come from?
- twin studies
- observations of familial aggregation
dizygotic twins share how much of their genome?
50%
if MZ twins share a trait less than 100% of the time, what does this suggest?
the trait is likely influenced by something other than genes (multifactorial)
why is linkage analysis used?
to determine whether the inheritance of a particular genetic marker predisposes to a particular disease/trait in a family
what are the steps in linkage analysis?
- determine how far apart the loci are by calculating the recombination frequency
- Determine the LOD score analyze the strength of evidence
what if the LOD score is about 3?
statistically sig evidence in favor of linkage
what if the LOD score is less than -2?
statistical evidence against linkage
what is the goal of an association study?
identify specific alleles for a particular disease / trait within an already designated gene region
what are the limitations of association analysis?
- evidence for association is not evidence for causation
- multiple SNP’s are needed becasue the marker allel needs to be closely linked to the disease locus
