using twin studies to estimate heritability

Question 1

what are complex diseases due to

Answer 1

alleles at a large number of different loci as well as environmental effects

Question 2

there is not much dispute that physical disorders have a genetic component. what is there much more dispute over

Answer 2

whether psychiatric disorders have a genetic component

Question 3

what is meant by additive variance

Answer 3

if you have 2 alleles at a locus the phenotypic outcome is a arithmetic sum of the alleles that are influencing it

Question 4

what is meant by dominant variance

Answer 4

influence of one allele affecte the outcome of the other (depends on the actual configuration of the alleles)

Question 5

what cannot be transmitted from parents to children

Answer 5

dominance effects

Question 6

what can twin studies do

Answer 6

disentangle the effects of gene and environment

Question 7

what is special about identical twins

Answer 7

have exactly the same genotype

Question 8

how much of the genotype do identical twins share

Answer 8

50%

Question 9

differences in identical twins are said to be from

Answer 9

experiences that one twin has but not the other twin

Question 10

If identical twins are considerably more similar than fraternal twins (which is found for most traits) what does this indicate

Answer 10

genes play an important role in these traits

Question 11

what does the acronym in the ACE model mean

Answer 11

A = additive effects
C = common environment
E = non shared environment

Question 12

what does the additive variance A of identical twins =

Answer 12

1

Question 13

what does the additive variance A of dizygotic twins =

Answer 13

0.5

Question 14

we make the assumption that the common environment (C) = what for both monozygotic and dizygotic

Answer 14

1

Question 15

what does the phenotypic correlation of monozygotic twins =

Answer 15

A + C

Question 16

he difference between the identical and fraternal correlations is due entirely to a halving of the genetic similarity, the additive genetic effect ‘A’ is simply twice the difference between the identical and fraternal correlations:. this can be written as

Answer 16

A = 2(rMZ-rDZ)

Question 17

how do we work out the effect of common environment using correlation of monoxygotic twins

Answer 17

C = rMZ - A

Question 18

how do we work out effect of non shared environment using correlation of monozygotic twins

Answer 18

E = 1 - rMZ

Question 19

what is additive variance ususally denoted as

Answer 19

h^2

Question 20

what are discontinuous traits measured by

Answer 20

concordance

Question 21

what does concordance mean

Answer 21

the presence of the same trait in both members of a pair of twins

Question 22

when can you say twins are “concordant”

Answer 22

twins are concordant when both have or both lack a given trait.

Question 23

A twin study compares the concordance rate of identical twins to that of fraternal twins. what can this help suggest

Answer 23

whether a disease or a certain trait has a genetic cause

Question 24

Because identical twins are genetically virtually identical, it follows that a genetic pattern carried by one would very likely also be carried by the other. If a characteristic identified in one twin is caused by a certain gene, then it would also very likely be present in the other twin. Thus, the concordance rate of a given characteristic helps suggest whether or to what extent a characteristic is related to genetics T/F

Answer 24

T

Question 25

DZT - what % have identical genotypes

Answer 25

25

Question 26

25% of any dominance effects in DZT will be shared

Answer 26

T

Question 27

how do dominance effects compare in monozygotic and dizygotic twins

Answer 27

any dominance effects will be shared by MZT but dominance effects will only be shared with 25% DZT

Question 28

what is meant by epistasis

Answer 28

phenotype of an allele at one locus is affected by the genotype of another locus

Question 29

what is meant by broad sense heritability

Answer 29

the degree to which a trait is genetically determined, expressed as the ratio of the total genetic variance to the phenotypic variance (VG/VP).

Question 30

what is narrow sense heritability

Answer 30

the degree to which a trait is passed from parent to offspring expressed as the ratio of the additive genetic variance to the total phenotypic variance (VA/VP).

Question 31

twin studies are nearer to estimating … sense heritability

Answer 31

broad

Question 32

what are the limitations to twin studies

Answer 32

• not representatie
• in utero environment is different for twins than it is for singular births (may be expoed to different levels of hormones)
• assumes MZT and DZT share environment

Question 33

across wide range of phenotypes about 50% of population variance is due to what

Answer 33

genetic variance