Lecture 4

Question 1

what kind of non-additive genetic variance is called dominance variance?

Answer 1

dominance variance: within locus (within gen) additivity

> interaction between alleles at a locus

Question 2

what is epistatic interaction?

Answer 2

epistatic interaction:

> interaction between loci

Question 3

what kind of genotypes exist at a biallelic locus?

what are the frequencies?

onder what assumption?

Answer 3

genotypes: AA, Aa, aa
frequencies: p², 2pq, q²

onder the assumption of random mating

Question 4

variance explained by linear regression is called…?

unexplained (residual) variance is called …?

Answer 4

explained by linear regression: additive genetic variance

unexplained: dominance genetic variance

Question 5

in the case of full dominance, how much of genetic variance explained by linear regression?

Answer 5

67,7%

Question 6

ADE model:

var( pheno) = ?

Answer 6

var(pheno) = var (A) + var (D)

if var(D) = 0 >>> linear model

in var(D) > 0 and var(A) >>> not plausible

Question 7

what are the expected correlations between twins an siblings in dominance variance?

Answer 7

var(D) correlations:

rMZ = 1

rDZ/Sibs = 1/4

rest = 0

Question 8

why is the ACDE model not identiefied?

Answer 8

only 3 observed statistics and 4 free parameters

observed:

1. 1 variance ( 4 but you assume them equal)
2. MZ covariance
3. DZ covariance

free:

1. A
2. C
3. D
4. E

Question 9

ACDE model not identified in classical twin design

> solution? (2)

Answer 9

1. extend your design so you can fit ACDE
2. fit either ACE or ADE

>>> rule of thumb: when

rDZ < 0.5 rMZ >>> fit ADE

rDZ > 0.5 rMZ >>> fit ACE

Question 10

heritability in the ADE Model

how to calculate narrow sense heritability?

how to calculate broad sense heritability?

Answer 10

narrow sense (additive genetic effects)

> A / A + D + E

broad sense (all genetic effects)

> A + D / A + D + E

Question 11

how to work with a sex limitation model

Answer 11

sex limitation model: use 4 groups defined by sex and zygosity

1) ACE contributions in males?
2) ACE contribution in females?
3. contributions equal in males and females?

Question 12

what parameters in a homogene sex limitation model?

what parameters in heterogene?

Answer 12

homo: a, c, e
hetero: Am, Cm, Em, Af, Cf, Ef

Question 13

sex limitation model: what group can be added?

what can be tested?

Answer 13

adding a 5th group

> DZOS (DZ opposite sex pairs)

>>> test if the A correlation is 0.5

>>> if rA < 0.5, genes in males and females may differ

Question 14

sex limited model. all parameters are unequal between males and females but rA = 0.5

> what could be the case?

> how to test for it?

Answer 14

could be a scalar sex limited model, no difference in variance components but only in total variance

> test if

Af = x*Am

Cf = x*Cm

Ef = x*Em

Question 15

Gene- environment interaction van be a misnormer.

why?

Answer 15

e.g. interaction between genes and SES

> is SES truly environmental and not depending on genes?

Question 16

what is one problem with detecting dominance using the classical twin model?

Answer 16

the power to detect dominance variance is low in classical twin studies

>> adding sibs can increase power

>> also: detection of twin - singleton differences

Question 17

non-additive genetic effects are present in many personality traits

> what does this suggest?

Answer 17

this suggests that personality is not neutral to selection

>>> neutral mutation plus random genetic drift tends to result in higher additive than non-additive genetic variation

Question 18

what does additive codominance stand for?

Answer 18

additive codominance = linearity (in regression)

>> dominance deviation parameter = 0