Genetics Lecture 4 - Multifactorial Inheritance

Question 1

Whom are association studies performed on?

Answer 1

Populations.

Question 2

Whom are linkage analyses performed on?

Answer 2

Families.

Question 3

Define multifactorial inheritance.

Answer 3

The combination of genetic and environmental factors in causation of a particular disease or trait.

Question 4

Define trait.

Answer 4

A distinct variant of a phenotype characteristic that may be inherited.

Question 5

Are single gene traits and polygenic traits affected by environmental changes?

Answer 5

No

Question 6

Are threshold traits penetrant?

Answer 6

No.

Question 7

Define liability in regards to threshold multifactorial traits.

Answer 7

Liability is the total combined genetic and environmental factors that influence the development of a multifactorial disorder or trait.

Question 8

When does one display phenotypic effects of a threshold trait?

Answer 8

When the liability threshold has been reached.

Question 9

Name some multifactorial disorders.

Answer 9

Cleft lip/palate, congenital hip dysplasia, plyoric stenosis, height.

Question 10

Is eye color a multifactorial trait?

Answer 10

No, its polygenic.

Question 11

What are the recurrence risk rules?

Answer 11

1. The greater the severity, the higher the recurrence risk.
2. Recurrence risk is higher if more than one family member is affected.
3. Recurrence risk decreases rapidly in more remotely related individuals.
4. Recurrence risk is greater if the proband is of the less commonly affected sex.
5. Recurrence risk for 1st degree relatives is approximately equal to the square root of the population incidence of the trait.

Question 12

What is the general recurrence risk for most isolated birth defects that follow multifactorial inheritance?

Answer 12

4%

Question 13

What did twin studies investigate?

Answer 13

Heredity (MZ vs DZ twins)

Question 14

How does the liability curve shift for a family who has a disease history for a multifactorial trait?

Answer 14

It shifts to the right of the population curve and comes back as the proband is more distantly related to affected family members.

Question 15

What is used to calculate the LOD score?

Answer 15

Recombination frequency.

Question 16

What is a classic environmental cause of neural tube defects?

Answer 16

Folic acid deficiency.

Question 17

Define familial.

Answer 17

Strong family history but no identifiable allele.