Multifactorial Disorders

Question 1

Define multifactorial inheritance and differentiate the impact that genetic traits have in multifactorial conditions versus conditions due to single gene or chromosomal defects.

Answer 1

Many conditions are noted to recur in families at an incidence higher than predicted by chance alone, but do not display typical Mendelian inheritance patterns either. We attribute this clinical observation to multifactorial Inheritance.

Question 2

Define concordance rates and heritability and determine which conditions have higher heritability based on concordance rates in monozygotic (identical) and dizygotic (fraternal) twins

Answer 2

Concordance Rate: How often two individuals share the same trait/condition.
-Diseases/traits among twins are determined to be concordant (shared) or discordant (not shared)
Determined solely by genes: 100% concordant among MZ twins :50% concordant among DZ twins
Determined solely by the environment: similar concordance rate among MZ and DZ twins
Heritability: Measures the proportion of the total variance of a trait that is caused by genes.
Heritability is determined by comparing the concordance rates between MZ and DZ twins
H = 2 (C MZ – C DZ)
•The greater the difference, the higher the heritability.
• If concordance rates are similar, heritability is low

Question 3

Describe gender-based differences in thresholds and explain how it influences the recurrence risk for members of different genders in the same family.

Answer 3

If the affected individual belongs to the less commonly affected gender (higher threshold of liability), the recurrence risk is higher than if the affected individual belongs to the more commonly affected gender (lower threshold

Question 4

What is a teratogoen?

Answer 4

A type of environmental factor that can contribute to congenital malformations that are multifactorial.

Question 5

What does heritability not tell you?

Answer 5

How many genes could be involved, how much each gene contributes to phenotype, and mode of inheritance.

Question 6

Describe Adoption Studies

Answer 6

Allow you to evaluate the effect on environment among individuals with shared genes. They compare adopted offspring of affected parents to adopted offspring of unaffected parents.

Question 7

What are the quantitative traits?

Answer 7

Polygenic traits: Variation in phenotype is thought to be a result of combined effects of multiple genes.
Multifactorial traits: When environmental influences also impact upon the variations noted in the phenotype of the trait.