Lecture 4: Multifactorial Inheritance Flashcards
What are two things that can contribute to an individual’s trait?
- Genes
2. Environment
Multifactorial Trait
A trait that results from the combined influences of multiple genes AND the environment.
Polygenic Trait
A trait that results from the combined influence of multiple genes, but NOT the environment.
Quantitative Traits
A multifactorial trait that can be measured on a numerical scale.
Follows a bell-shaped distribution in populations.
E.g. Height, weight, and BP.
Threshold Traits
A multifactorial trait that is either present, or absent.
Follows a bell-shaped distribution in a population with respect to LIABILITY to a trait. Only those exceeding the threshold on the liability scale with exhibit the trait.
E.g. Club foot, diabetes, cleft lip.
What are four signs of Multifactorial Inheritance?
- Familial concentration without a set pattern of inheritance.
- Absence of clear biochemical defects resulting from a single abnormal gene.
- Considerable variation in severity and expression of the phenotype.
- Gender differences in the frequency of occurrence.
Empiric Risks
Risks for recurrence in regards to multifactorial traits that are based upon population and family studies.
True or False?
Risk of occurrence and recurrence is often the same for males and females.
False.
Risks are often different.
True or False?
Recurrent risks of multifactorial traits are typically less than recurrence risks of single gene disorders.
True.
However, there is not insignificantly less risk.
Proband
A person serving as the starting point for a genetic study of a family.
True or False?
In regards to common birth defects, the recurrence risk is less if the proband is of the less commonly affected sex.
False.
The recurrence risk is greater if the proband is of the less commonly affected sex.
Though precise recurrence risks for common birth defects vary substantially, what is a good number to remember?
4%
The recurrence risk for first-degree relatives is…
…approximately the square root of the population incidence of the trait.
List four types of evidence for heritability:
- The disease is more common in biologic relatives than in non-biologic relatives (such as spouses).
- Monozygotic twins are more frequently concordant than dizygotic twins.
- Monozygotic twins reared separately have greater concordance than expected by chance.
- Adopted children better resemble their biologic parents than adopted.
What is liability?
Total combined genetic and environmental factors that influence the development of a multifactorial disorder or trait.
Only those who exceed the threshold of liability will express.
Liability cannot be measured, it is determined from the incidence of the disease in a group, using statistics of the normal distribution.
