Multifactorial Inheritance

Question 1

what is a disease with multifactorial inheritance?

Answer 1

disease that has increased risk to family inheritance but no specific pattern for inheritance. Disease relies strongly on multiple genes and environmental factors

Question 2

what are “simple” Mendilian traits?

Answer 2

patient has a certain allele which gives the patient a “trait”. different alleles have different severity of that trait

Question 3

what are traits of complex traits? 4

Answer 3

1. aggregate in families
2. do not follow simple mendelian mode of inheritance
3. likely due to variants in multiple genes and non-genetic factors that may interact
4. no simple relationship btw genetic variant and trait when looking at population

Question 4

how is the relationship between genes and environment studied?

Answer 4

twin studies, look to see if they develop the same disease, better if live in different environments

Question 5

What are twins called that are identically matched for DNA sequence, age, and gender?

Answer 5

monozygous twins (MZ)

Question 6

what are twins called that on average share 1/2 of their DNA sequences?

Answer 6

Dizygous (DZ) twins

Question 7

If concordance rates are much higher in MZ twins than DZ twins, what does this suggest?

Answer 7

genetic variation contributes more to the risk of disease rather than environmental factor

Question 8

what does a higher correlation in any statistic indicated in MZ twins?

Answer 8

that the disease proliferation is likely due to genetic factors

Question 9

how is the heritability of a trait measured?

Answer 9

proportion of total “variance” in a trait that is due to “variation” in genes

Question 10

what does a high heritability imply?

Answer 10

differences in the population are due to differences in the genetic makeup of the individuals

Question 11

incomplete penetrance

Answer 11

not everyone with predisposing variant develops disease

Ex: Type I DM and MHC

Question 12

variable expressivity

Answer 12

no two individuals with the same genetic variant have exactly the same diseases characteristics
Ex. Maturity Onset Diabetes in the Young (MODY)

Question 13

Heterogeneity

Answer 13

the “same” disease can be caused by different alleles at one location or by alleles at different locations in the genome
ex allele: cystic fibrosis
ex locus: Alzheimer Disease

Question 14

Presence of phenocopies

Answer 14

individuals who have disease or trait for reasons that are not primarily genetic even though clinical presentation is similar to genetic version
Ex. Thalidomide-induced limb malformation vs genetically induced

Question 15

what are the characteristics of complex traits?

Answer 15

must demonstrate one or more of the following

1. incomplete penetrance
2. variable expressivity
3. heterogeneity -allele and locus
4. presence of phenocopies