Lecture 4 Flashcards
what kind of non-additive genetic variance is called dominance variance?
dominance variance: within locus (within gen) additivity
> interaction between alleles at a locus
what is epistatic interaction?
epistatic interaction:
> interaction between loci
what kind of genotypes exist at a biallelic locus?
what are the frequencies?
onder what assumption?
genotypes: AA, Aa, aa
frequencies: p², 2pq, q²
onder the assumption of random mating
variance explained by linear regression is called…?
unexplained (residual) variance is called …?
explained by linear regression: additive genetic variance
unexplained: dominance genetic variance
in the case of full dominance, how much of genetic variance explained by linear regression?
67,7%
ADE model:
var( pheno) = ?
var(pheno) = var (A) + var (D)
if var(D) = 0 >>> linear model
in var(D) > 0 and var(A) >>> not plausible
what are the expected correlations between twins an siblings in dominance variance?
var(D) correlations:
rMZ = 1
rDZ/Sibs = 1/4
rest = 0
why is the ACDE model not identiefied?
only 3 observed statistics and 4 free parameters
observed:
- 1 variance ( 4 but you assume them equal)
- MZ covariance
- DZ covariance
free:
- A
- C
- D
- E
ACDE model not identified in classical twin design
> solution? (2)
- extend your design so you can fit ACDE
- fit either ACE or ADE
>>> rule of thumb: when
rDZ < 0.5 rMZ >>> fit ADE
rDZ > 0.5 rMZ >>> fit ACE
heritability in the ADE Model
how to calculate narrow sense heritability?
how to calculate broad sense heritability?
narrow sense (additive genetic effects)
> A / A + D + E
broad sense (all genetic effects)
> A + D / A + D + E
how to work with a sex limitation model
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?
what parameters in a homogene sex limitation model?
what parameters in heterogene?
homo: a, c, e
hetero: Am, Cm, Em, Af, Cf, Ef
sex limitation model: what group can be added?
what can be tested?
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
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?
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
Gene- environment interaction van be a misnormer.
why?
e.g. interaction between genes and SES
> is SES truly environmental and not depending on genes?
what is one problem with detecting dominance using the classical twin model?
the power to detect dominance variance is low in classical twin studies
>> adding sibs can increase power
>> also: detection of twin - singleton differences
non-additive genetic effects are present in many personality traits
> what does this suggest?
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
what does additive codominance stand for?
additive codominance = linearity (in regression)
>> dominance deviation parameter = 0
