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NEUR3302 > Wk3 Cognitive Genetics > Flashcards

Wk3 Cognitive Genetics Flashcards

1
Q

what do genes basically do?

A

code for a protein product

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2
Q

what could be the consequences of slight variation in protein expression?

A

alterations in brain function and structure between people

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3
Q

what is the basic idea/model of how cognitive genetics works?

A

genetic variation -> protein expression -> brain (structure/function) -> cognition

genes affect cognition through the above pathway

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4
Q

what is a genotype?

A

variation in genes across people

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5
Q

what is the aim of cognitive genetics?

A

linking genetic variation to variation in cognitive abilities

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6
Q

what are three ways to investigate genotypes?

A

twin studies
candidate genes
genome wide association

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7
Q 
def complex trait. 
what influences it? 3
A

a quantifiable property of an organism

influenced by

  • multiple genes
  • enviornmental factors
  • interactions between them
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8
Q

phenotype?

A

physical appearance of an organism with respect to a trait

how a complex trait manifests

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9
Q

endophenotype?

A

measurable components that lie along the causal pathway between disease (phenotype) and distal genotype

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10
Q

why examine an endophenotype?

A

can be hard to examine the full expression of a phenotype. e.g. complex clinical diagnoses are required for ADHD vs easier to look at sustained attention as an aspect of the full trait

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11
Q

what is an advantage to investigating an endophenotype? consequence?

A

simpler and easier to measure (than a complex trait) ,

so possibly controlled by fewer genes.

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12
Q

what makes up the genome?

A

23 pairs of chromosomes, in each pair one comes from each parent

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13
Q

what is a gene?

A

length of DNA that specifies a particular protein product

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14
Q

what is an allele?

A

one of two or more forms of a gene (different versions of the same gene)

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15
Q

what does homozygous mean?

A

the same alleles on both chromosomes (mother and father)

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16
Q

what does heterozygous mean?

A

different alleles (forms of the same gene) at each chromosome

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17
Q

if you got different alleles from your mother and father this gene is ___

A

heterozygous

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18
Q

what are two common types of genetic variation?

A

single nucleotide polymorphisms (SNP)

variable number of tandem repeats (VNTR)

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19
Q

what is a single nucleotide polymorphism?

A

when alleles differ at a single base pair (or one location)

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20
Q

if AAGCCTA differs from AAGCTTA, this is a ___

A

single nucleotide polymorphism

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21
Q

what is a VNTR?

A

a location in a genome where a short nucleotide is organised as a tandem repeat of a particular (variable length, 10 -100)

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22
Q

how are individuals classified using VNTR?

A

based on how many copies of the repeat length of interest they have: 0, 1, or 2.

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23
Q

what is a polymorphism?

A

the presence of two or more variants (alleles) in a gene or DNA sequence in a population

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24
Q

what are the most common polymorphisms?

A

SNPs

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25
Q

what does a SNP reflect?

A

a change in a single base in the DNA that differs from the usual base at that position

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26
Q

a polymorphism in the length of tandemly repeated short sequences of DNA is called ___

A

VNTR

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27
Q

2 phenotypical aspects of ADHD required for diagnosis

A

inattention

hyperactivity/impulsivity

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28
Q

what would be an endophenotype in ADHD?

A

sustained attention

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29
Q

def sustained attention

A

ability to maintain goal-directed focus in the absence of exogenous or external cues

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30
Q

what task can test sustained attention? how does it measure it?

A

SART: sustained attention to reaction time

behaviourally

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31
Q

what does a SART task involve?

A

press or don’t press a button, in response to a cue presented earlier

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32
Q

what is an advantage of heritability/twin studies?

A

they can measure both genetics and environment and compare their interaction

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33
Q

what is a disadvantage of heritability/twin studies?

A

they can’t specify which genes, only that genes are important

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34
Q

what are the 3 influences in a twin study model?

A

additive genetic influences
shared environmental influences
non-shared environmental influences

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35
Q

what could you conclude if MZ twins have low correlation on an ability/trait? why?

A

differences are due to non-shared environments

MZ twins share genes and environment

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36
Q

what could you conclude if there are high correlations of a trait/ability in both MZ and DZ twins? why?

A

effects are due to shared environment

differences in % of shared genes between DZ & MZ did not produce an influence

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37
Q

what could you conclude if there are high correlations in a trait/ability for MZ twins, but low correlations for DZ twins? Why?

A

effects are due to genetics

100% shared genes in MZ twins is the only extra factor that could account for increased twin similarity

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38
Q

heritability estimate for ADHD?

A

60-90%

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39
Q

describe the dose effect of genes on ADHD

A

unaffected siblings perform better on sustained attention but worse than healthy controls

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40
Q

heritability estimates for sustained attention change ___ . how?

A

with age

less influence the older you get

41
Q

heritability estimate for sustained attention in children

A

46-72%

42
Q

what was the biggest driver of classroom behaviour in children from wales vs london (davis et al) ? where was this found?

A

non-shared environment

biggest in london but differed across UK

43
Q

what did Davis et al conclude about heritability of classroom behaviour across UK? what was their geocoding evidence ?

A

diverse environments give more possibility for non-shared environmental influence
london had the greatest variance in household income AND the greatest influence of non-shared environment on behaviour

44
Q

what did a huge geocoding survey (Davis et al) find about ADHD expression and genes? what was their conclusion?

A

genes had a bigger influence on ADHD in london

some aspect of the environment is necessary to allow gene’s to express a phenotype

45
Q

why is it not enough to have a gene that is capable of expressing a phenotype? (eg?)

A

genes may not show the phenotype if there is not an environment to display it in

eg: you may have a gene for allergies, but never have hayfever if you don’t live next to a field

46
Q

what was the Scarr-Row hypothesis about nature/nurture interactions for IQ?

A

genes > environment influence for advantaged groups compared to disadvantaged groups

47
Q

in Davis et al twin study on ADHD in UK: twins were aged __ when tested. each pair was __ based on __

A

12
geocoded
postcode

48
Q

in Davis et al twin study on ADHD in UK: 45 phenotypes were investigated including ___ 3

A

IQ
ADHD
school achievement

49
Q

Why is the influence of poverty on IQ dependent on country/culture?

A

low SES people have different access to basic needs in richer vs poorer countries

50
Q

where was a gene x SES interaction found to occur?

A

only in the US

51
Q

what is the biggest determinant of IQ for low SES vs high SES americans?

A

low SES: environment > heritability

high SES: genes > environment

52
Q

def heritability and how it is estimated

A

proportion of variance explained by genetic factors for a certain phenotype
concordance rates of MZ and DZ twins

53
Q

def gene x environment interactions

A

when relationships between experience and altered behaviour/physiology is moderated by individual differences in genes (ie. polymorphisms)

54
Q

candidate gene studies involve a ____ selection of specific genes

A

theory driven

55
Q

what do candidate gene studies investigate?

A

how the candidate gene influences individual differences in a specific cognitive process

56
Q

how many possible versions of a SNP could people in a population have?

A

3

eg c/t, t/t, c/c alleles

57
Q

what is the selction of a candidate gene based on? 4

A

pharmacology
brain imaging
animal research
behavioural studies

58
Q

what NT system is important for ADHD candidate gene selection?

A

dopamine

59
Q

sustained attention brain network overlaps with

A

the network for the dopamine system

60
Q

experimental depletion of dopamine leads to

A

sustained attention deficits

61
Q

what is the most commonly used medication for ADHD? is effective in __ of cases.

A

methylphenidate (MPH)

60%

62
Q

clinical benefit of MPH is often attributed to action on __

A

blockade of the dopamine transporter (DAT)

63
Q

MPH significantly improves sustained attention deficits in children and adults but only for ___

A

those with ADHD

64
Q

where is the dopamine transporter protein DAT1 found?

A

caudate nucleus

65
Q

MPH makes dopamine have a stronger effect in the brain how?

A

stops DAT1 from clearing away DA (inhibiting uptake)

66
Q

what is the most commonly studied variant of DAT1 genes? the most frequent allele has how many variable repeats?

A

a VNTR in the 3’UTR (intron)

10 or 9

67
Q

Ps with one copy of the 10-repeat dopamine transporter allele (10/10 or 9/10) have ____ compared to ___

A

higher dopamine transport density

9/9 carriers

68
Q

children with ADHD that are homozygous for the 10 repeat DAT1 allele perform ___ than ___

A

more poorly on sustained attention tasks

children with other genotypes

69
Q

MPH makes dopamine act __

A

for longer

70
Q

what is a conclusion about one genetic effect and mechanism of ADHD?

A

selective attention is impaired because DAT1 (uptake protein) produces low persistence of DA

71
Q

what function describes the effect of Dopamine on task performance?

A

inverted-U

72
Q

what types of cognitive impairment might be found at the extremes of dopamine levels?

A

too little: inattention & drowsiness

too much: anxiety & dysphoric psychosis

73
Q

DRD4 is a ___

A

dopamine receptor gene

74
Q

what is the most commonly studied varients of DRD4 ? what are the most frequent alleles?

A

VNTR in exon 3

7-repeats or 4-repeats

75
Q

DRD4 has been show to affect __ and is predominantly expressed in the __

A

receptor function

prefrontal cortex

76
Q

how is DRD4-7R associated with endophenotypical expression of ADHD?

A

2 studies find children with 7Repeat better at sustained attention task, but another study found the opposite

77
Q

what is the difference between children with ADHD who have 7-repeat allele of DRD4 and those who don’t?

A

with: display extreme behaviour but no cognitive symptoms
without: at risk for poorer cognition

78
Q

what was the neurological difference between children with ADHD who have 7-repeat allele of DRD4, and those with 4-repeat allele?

A

larger prefrontal grey-matter for 7R than 4R

79
Q

2 things suggesting DRD4 is beneficial for ADHD

A

it protects against negative cognitive effects of ADHD

greater prefrontal volume

80
Q

def candidate gene

A

a gene with a function that suggests it is involved in the variation observed for a particular trait/phenotype

81
Q

def homozygous

A

having the same alleles at a gene locus on homologous chromosomes

82
Q

def heterzygous

A

having two different alleles at a particular gene locus on homologous chromosomes

83
Q

def exon

A

a protein coding portion of a gene

84
Q

def intron

A

a nucleotide sequence in a gene that does not code for the gene product

85
Q

most widely used form of gene studies is __

A

candidate studies

86
Q

genome wide association studies investigate __

A

variation in genes across the entire genome and how this influence individual differences in cognitive processes

87
Q

why are genome-wide association studies somehwat problematic for psychological studies?

A

psychological/cognitive tests are not reliable enough to have low noise when testing thousands of people

88
Q

what is the theoretical tradeoff between strength of genetic effects and allele frequency in genome wide association studies? what are the consequences of this?

A

common gene variants have small effects and rare variants have large effects
rare variants with small effects are hard to identify and there are few examples of common variants having large effects on common diseases

89
Q

what did a genome wide association study reveal about candidate genes for ADHD? what new genes were revealed?

A

none of the candidate genes previously investigated were significant at the genome wide level

genes related to neural development FOXP2 & DUSP6

90
Q

re: gene underpinnings of ADHD, it is likely __

A

polygenetic

91
Q

def GWAS

A

study that surveys most of the genome for causal genetic variants

92
Q

def genome

A

the entirety of an organism’s hereditary information

93
Q

what is ‘genome-wide significance’?

A

significance threshold in GWAS is 5 x 10^-8, due to bonferroni correction for 1 million SNPs being tested

94
Q

what are strengths of candidate gene studies? 3

A

can test specific hypotheses
greater power than GWAS
inexpensive

95
Q

what are weaknesses of candidate gene studies?2

A

not all possible genes are investigated

theory can miss some genetic effects

96
Q

GWAS are hypothesis-__

A

free

97
Q

strengths of GWAS 2

A

no prior info/theory needed

entire genome

98
Q

cons of GWAS

A

expensive

large samples needed for effects to survive correction for multiple comparisons (1 million SNPS)

99
Q

how can genetic influence information help? 5

A 
improved diagnosis
improved treatment 
development of environmental interventions
understand bio- mechanisms
understand co-morbidity

NEUR3302 (7 decks)

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