6 Multifactorial

Question 1

what is multifactorial inheritance?

Answer 1

combined contribution of genes and environmental factors in the causation of a particular disease or trait

Question 2

what is a quantitative trait?

Answer 2

• 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

Question 3

what is a threshold trait?

Answer 3

-something is either present or absent, not a gradient

Question 4

what is liability?

Answer 4

total combined genetic and environmental factors that influence the development of a multifactorial disorder or trait

Question 5

can liability be measured?

Answer 5

no, it is determined by the incidence of the disease in a group, using statistics of the normal distribution

Question 6

liability may differ between genders? T/F

Answer 6

True

Question 7

recurrence risk is more or less clear in multifactorial traits

Answer 7

less

Question 8

if the proband is more sever, this means there is a greater or lesser RR?

Answer 8

greter

Question 9

more family members having the disease does what to the RR?

Answer 9

goes up

Question 10

in more distantly related relatives, what happens to RR?

Answer 10

drastically goes down

Question 11

what happens to the RR if the proband is of the less commonly effected sex

Answer 11

goes up

Question 12

what is the RR for first degree relatives in multifactorial inheritance?

Answer 12

approximately the square root of the population incidence

Question 13

in general, what is the RR for most isolated birth defects?

Answer 13

approximately 4%

-however, if it is part of an underlying genetic syndrome then the RR could be much higher

Question 14

how would you study if a trait is due to genes, the environment, or both?

Answer 14

-estimate heritability: how much of the phenotype is based on genetics

Question 15

where does evidence of genetic contribution to a disorder come from?

Answer 15

• twin studies

- observations of familial aggregation

Question 16

dizygotic twins share how much of their genome?

Answer 16

50%

Question 17

if MZ twins share a trait less than 100% of the time, what does this suggest?

Answer 17

the trait is likely influenced by something other than genes (multifactorial)

Question 18

why is linkage analysis used?

Answer 18

to determine whether the inheritance of a particular genetic marker predisposes to a particular disease/trait in a family

Question 19

what are the steps in linkage analysis?

Answer 19

1. determine how far apart the loci are by calculating the recombination frequency
2. Determine the LOD score analyze the strength of evidence

Question 20

what if the LOD score is about 3?

Answer 20

statistically sig evidence in favor of linkage

Question 21

what if the LOD score is less than -2?

Answer 21

statistical evidence against linkage

Question 22

what is the goal of an association study?

Answer 22

identify specific alleles for a particular disease / trait within an already designated gene region

Question 23

what are the limitations of association analysis?

Answer 23

• 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