Multifactorial Inheritance

Question 1

describe the liability/threshold model

Answer 1

• If you have only “good” genes you can have a lot of “bad” environment and still be okay
• But if you start out with some “bad” genes, it does not take much “bad” environment to tip you over the edge

Question 2

describe familial relative risk

Answer 2

• the more closely related you are to someone with a complex disorder, the more likely you are to have some of the same alleles
• but that risk drops by half for every degree distance from affected person

Question 3

describe familial aggregation and relative risk

Answer 3

• familial aggregation of a disease may be estimated by comparing the frequency (prevalence) of the disease in the relatives of an affected proband with its freq. in the gen. pop.
• this is the relative risk ratio = λ
• λ = (prevalance of disease in relatives of affected person)/(prevalence of disease in general pop)

Question 4

describe characteristics of multifactorial inheritance

Answer 4

• trait does not demonstrate a simple Mendelian pattern of inheritance
• familial aggregation
• more common among the close relatives of the proband and less common in relatives who are less closely related

Question 5

describe concordance in MZ twins

Answer 5

• concordance means both twins have the same disease
  
  • concordance = 100% if genetically determined
  • concordance < 100% if non-genetic factors involved
• discordance means one has it but the other does not
• If concordance similar between MZ and DZ, environment plays a big role
• If concordance different between MZ and DZ, genes play a big role

Question 6

name 2 neural tube defects

Answer 6

• Anencephaly
  
  • most severe of the neural tube defects
  • rare and fatal
  • underdeveloped brain and incomplete skulls
• spina bifida
  
  • incomplete closure of the spine
  • repair may be done in utero or postnatally
• BOTH show multifactorial inheritance
  
  • supplementation of the mother’s diet with folate can reduce the incidence of neural tube defects by ~70%