Lecture 7: Multifactorial Inheritance Flashcards
True or False: Multifactorial traits tend to cluster in families but do not follow a recognizable inheritance pattern
True
Multifactorial traits can either be ____ or ____
quantitative (continuous) or qualitative (discontinous)
Which traits exhibit phenotypic variability due to additive contribution of genetic and environmental factors?
A. Continuous (quantitative)
B. Discontinuous (qualitative)
A. Continuous (quantitative)
Which traits are expressed as “all or none” once a threshold of predisposing insults is exceeded?
A. Continuous (quantitative)
B. Discontinuous (qualitative)
B. Discontinuous (qualitative)
True or False: If a condition is common in a population AND an affected individual’s relatives have a LOWER incidence of the disease than for a single gene disorder but a HIGHER risk than the general population, this suggest complex inheritance
True
A proband’s siblings and offspring have similar incidence of a disease. Dose this suggest complex inheritance?
Yes!
If a disease incidence in a proband’s relatives increases rapidly with every degree of separation, does this suggest complex inheritance?
No! - If it were a complex disease, you would expect disease incidence in a proband’s relatives to DECREASE rapidly with every degree of separation
The disease incidence of X condition in relatives of a proband is LOWER when the proband is of the LEAST commonly affected sex. Does this suggest complex inheritance?
No - if condition X was inherited complexly, you would expect the disease incidence of X condition in relatives of a proband to be HIGHER when the proband is of the LEAST commonly affected sex
True or False: In complex inheritance, observed risk rises following birth of two affected children
True
True or False: In complex inheritance, disease incidence in a proband’s relatives INCREASES with the severity of phenotypic manifestation in the proband
True
The more closely two people are relayed, the more ___ they share
alleles
The higher the frequency of shared alleles between proband and their relatives , the higher the correlation to the expression of the ___
trait
Height, body weight, BP, serum cholesterol are all examples of:
A. Continuous/quantitative traits
B. Discontinuous/qualitative traits
A. Continuous/quantitative traits
True or False: Continuous/quantitative traits are determined by the additive effects of multiple genes AND environmental factors
True
“Multiple additive locus model”
True or False: Qualitative traits tend to follow a normal Gaussian Curve in populations
False - quantitative traits do!
True or False: In quantitative traits, each predisposing gene allele (quantitative trait loci - QTL) and environmental factor contributes a small degree to overall expression of the trait
True
True or False: There is phenotypic variability in multifactorial complex inheritance
True
True or False: Multifactorial traits with complex inheritance are monogenic
False - polygenic
____ twins have same allele at every locus while first degree relatives have about ___
100%; 50%
Siblings and dizygotic twins share an average of __ of alleles across all loci
50%
True or False: Multiple additive locus model is associated with qualitative traits
False - quantitative!
Do discontinous/threshold traits follow a normal Gaussian distribution in populations?
No! - you either have it or don’t
In Discontinuous (Threshold) Traits, additive effects of genes and environment ___ to variable expression of a trait
A. Do
B. Do NOT
B. do NOT
In Discontinuous (Threshold) Traits, additive effects of genes and environment accumulate until a ___ is met
threshold
True or False: Discontinuous (threshold) traits applies to most common multifactorial disorders
True
In discontinuous (threshold) traits, additive effects of multiple gene alleles and environmental influences accumulate until a certain threshold level is exceeded. What happens once it is exceeded?
Disease phenotype is expressed
True or False: Once disease threshold is reached in discontinuous (threshold) traits, additive effects of multiple genes alleles and environmental influences can cause INCREASED severity of disease manifestation
True
____: Combined influences of multiple genetic and environmental insults are a person’s
Liability
True or False: The liability for a given multifactorial disorder does follow a normal gaussian distribution
True
Individuals on the high end of the liability distribution carry ___ genetic and environmental risk factors and are at ___ risk of developing the disease
high
True or False: There is familial aggregation in quantitative traits
False - qualitative traits
In qualitative traits, why does the risk to family members of expressing the disease phenotype remain higher than the general population?
Threshold remains
True or False: Pyloric stenosis is a multifactorial condition with unequal sex ratios
True (male:female, 5:1)
- Therefore, different liability thresholds for male and females
The disease risk of what type of traits rises with affected siblings?
A. Continuous
B. Discontinuous
B. Discontinuous
In pyloric stenosis, disease risk rises if affect relative is of _____ sex
A. most often affected sex
B. less often affected sex
B. less often affected sex
True or False: In pyloric stenosis, the least commonly affects sex must acquire more ____ (gene mutations) to express disease phenotype
liability factors
True or False: In pyloric stenosis, close relatives if an affected female share the HIGHER mutations burden and are more apt to acquire the disorder
True
Which of the following couples has the highest risk of a having a baby affected with pyloric stenosis?
A. Couples in which the father was affected with pyloric stenosis in infancy
B. Couples in which mother was affected with pyloric stenosis in infancy
B. Couples in which mother was affected with pyloric stenosis in infancy
RA is a multifactorial disorder affecting girls 3x more often than boys. Which of the following is at the highest risk of being affected?
A. Boy with affected male cousin
B. Boy with affected brother
C. Girl with affected uncle
D. Girl with affected brother
E. Girl with affected niece
D. Girl with affected brother
Hypertrophy and thickening of pylorous muscles, which blocks food from entering small intestine from the stomach is a feature of which condition?
Pyloric Stenosis
The recurrence risk for first degree relatives of a proband of a multifactorial disease can be approximated by calculating the ____ of disease incidence of the general population
square root
True or False: Cleft lip and palate arises due to both genetic and environmental mechanisms
True
Which type of CL/P occurs if the cause is:
- Single gene mutation
- Chromosomal disorders
- Teratogens
A. Non-Syndromic
B. Syndromic
B. Syndromic
Which type of CL/P occurs if the cause is due to environmental causes (folic acid deficient during pregnancy, uncontrolled maternal diabetes, maternal smoking)
A. Non-Syndromic
B. Syndromic
A. Non-Syndromic
True or False: ~2/3 of Non-Syndrome CL/P patients are male
True
Non-syndromic patients are often sporadic cases with complex ____
inheritance
Which two factors increased risk of CL/P?
- Disease severity in affected relatives
- # of affected parents or relatives
- disease risk rises with increased phenotypic severity of affected proband
True or False: The more severe the manifestation of a multifactorial condition, the greater the probability of its recurrence in the family
True
How can you determine the risk of recurrence in multifactorial diseases for 1st degree relatives?
Take the square root of the disease incidence in the general population
The overall incidence of CL/P is 1/1000.
For a family with no history of CL/P, what is the probability that any pregnancy will result in an affect child?
Occurrence risk is the same as the overall incidence in general population (1/1000)
For a family in which a child is born with CL/P, what is the result that any subsequent pregnancy will result in an affected child?
Square root of 1/1000 = 1/32 = 3.1%
_____: assesses the extent to which one’s genetic makeup influences expression of a trait
Heritability
What are examples of non-genetic factors that can impact the heritability of complex traits?
- Environmental exposures (diet, infection)
- Somatic mutation
- Epigenetic gene expression changes
How do you estimate heritability from concordance rates in twins?
True or False: The higher the heritability, the greater role genetic background plays in developing traits
True
Which of the following is inherited according to the discontinuous model of muti-factorial inheritance?
A. BP
B. Duchenne Muscular Dystrophy
C. Height
D. Non-syndromic cleft lip/palate
E. Body weight
D. Non-syndromic cleft lip/palate
The concordance rate for MS in MZ twins is 0.28 and in dizygotic twins it is 0.03. What is the heritability of MS?
A. 1
B. 0
C. 0.25
D. 0.5
E. 2.0
D. 0.5
