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1

What are multifactorial disorders?

Diseases that result from the influence of multiple genes, and often with the additional influence of the environment

2

Match the frequency of disease with the correct cause (genome/chromosome mutations, multifactorial disorders, single gene mutations): 50/1000, 6/1000, 10/1000

6/1000: disorders due to genome/chromosome mutations
10/1000: disorders due to single gene mutations
50/1000: multifactorial disorders

3

What are the primary characteristics of multifactorial disorders?

1. Occurs more frequently in relatives of an affected individual than in the general population (relative risk ratio >1)
2. Does not follow classical Mendelian inheritance patterns
3. Recurrence risk for a family member is determined using empirically derived risk tables when available

4

Mendelian traits are ___ (present or not).

Qualitative/dichotomous

5

Mendelian traits are always attributable to different ___ of a single ___.

Alleles; gene (wild type or mutant)

6

Complex traits are either ___ or ___.

Continuous/quantitative; qualitative

7

Quantitative traits are described by a ___ distribution of numerical values about a population ___.

Gaussian (normal); mean

8

What are the x and y variables of a Gaussian distribution?

X: numerical value for quantitative trait
Y: # of individuals with a given X

9

What is sigma?

Standard deviation; square root of variance

10

What is variance?

Degree of spread to either side of the mean; sigma squared

11

What is the multigenic theory of quantitative traits?

Traits governed by a large number of factors (genes) would display the same type of continuous distribution as seen for quantitative traits.

12

What is the polygenic theory of discontinuous traits?

The concept of threshold allows for the continuous distribution of values about a mean to characterize polygenic traits.

13

Family members share a greater number of identical ___ of genes than unrelated individuals

Alleles

14

The ___ for a genetic disorder within a family exceeds the frequency of the disease in the general population.

Recurrence risk

15

What is relative risk ratio?

Lambda R; a quantitative measure of the degree of familial aggregation of a disease; quantity>1 suggests genes contribute to the disease

16

What does relative risk ratio equal?

Prevalence of disease in relatives of affected person/Prevalence of disease in general population

17

Family members may also share ___ in common.

Environmental factors

18

What is concordance?

Likelihood that an individual will share a common phenotype with another family member (have the same disease)

19

The number of alleles two family members share in common is determined by ___.

The degree of relatedness

20

Because concordance rates are not 100% and 50% in monozygotic and dizygotic twins respectively, it is likely that...

...other factors are contributing.

21

What is strong evidence of a genetic component to a specific disease with respect to twins?

Monozygotic twins show greater concordance than dizygotic twins.

22

What suggests that genetic factors are more important than environmental factors to a specific disease?

Similar concordance rates for MZ twins reared together and apart

23

Variance is related to the contribution of ___ and ___ to the trait.

Genes; environment

24

When variance is due to different causes, they are ___.

Additive

25

variance = ?

v(environment) + v(genes)

26

What is heritability and what does it equal?

The proportion of the total variance due to genes
h^2 = v(genes)/[v(environment)+v(genes)]

27

What is the variance of MZ twins?

v(MZ) = v(environment) because there is not variance in genes

28

What is the variance of DZ twins?

v(DZ) = v(environment) + v(genes)

29

h^2 can also be written as = ___ with respect to twins.

[v(DZ)-v(MZ)]/v(DZ)

30

What does heritability of 0 indicate? Of 1?

0 - variability due to environment exclusively
1 - variability due to genes exclusively