behavioural genetics 2 Flashcards
1
Q
Mendel (1822-1884)
A
- studied dichotomous traits
–> one form or another
–> NEVER in combination - quite different to what psychologists tend to focus on (tend to focus on traits on a spectrum/scale)
2
Q
Mendel’s pea pods summary
A
- Green pods (GG) bred with yellow pods (yy)
–> GG x yy - first gen of offspring were green
–> Gy - second gen of offspring had ratio of 3:1
–> 3 green (Gy)
–> 1 yellow (yy)
3
Q
phenotype
A
- physical manifestation of the genotype
- trait/characteristic
–> e.g. blue eyes
4
Q
genotype
A
the genetic material
5
Q
allele
A
different forms of a gene that control the same trait
–> e.g. G vs y
6
Q
heterozygous
A
- one dominant allele and one recessive allele
–> e.g. Gg
7
Q
homozygous
A
- same type of allele
- two dominant or two recessive
- e.g. GG or yy
8
Q
Dominant and recessive
A
- dominant = capital letter (G)
- recessive = lower case letter (g)
–> recessive need two alleles to present the characteristic
9
Q
gene for serotonin transporter
A
- gene for serotonin transporter (reuptake of serotonin into the presynaptic neuron - ready for rebuilding in vesicles) has 2 forms
1. long (l)
2. short (s) - both are recessive
- l isn’t recessive to s
10
Q
forms of serotonin transporter
A
- short form (s) associated with higher incident rate of depression
11
Q
additive genes?
A
- both l and s are recessive
- they are additive
- heterozygous genotypes lead to about 50% of each
–> e.g. ls will lead to about 50% long and 50% short - homozygous will produce all of one type
–> e.g. ss will produce all short proteins - additive genotypes do not produce a definitive phenotype due to dominance, rather the effects of genotypes sort of add up
12
Q
additive genes and the variance equation
A
- Vp = A squared + C squared + E squared
- A is the ADDIDITVE genetic component
13
Q
why two alleles in a genotype?
A
- alleles refer to chromosomes
- chromosomes come in pairs
- autosomes = all other traits, practically identical (22 pairs)
- allosomes = sex chromosome (XX or XY)
14
Q
chromosomes and DNA
A
- made of DNA
- DNA is made up of 4 bases:
1. adenine
2. Thymine
3. Cytosine
4. Guanine - in 2 pairs
- AT, GC (@ gemma collins)
15
Q
what does DNA do?
A
- replicates
- double helix (2 strands) unwind
- exposed pairs line up with each strand
- 2 new complementary strands form - makes proteins
- DNA unwinds, complementary strand of mRNA lines up
–> old DNA and ONE NEW mRNA
–> uses tRNA, have codes which bind to complementary codes on the mRNA, amino acids on tRNA bind together
16
Q
RNA recap
A
- ribose
- uracil not thymine
- base pairs = AU, GC
17
Q
the Tryptophan Hydroxylase gene (+ mutations)
A
- enzyme that makes serotonin
- mutant forms of the gene can result in less serotonin cells
–> in vitro (grown in a dish) cell with this gene made 80% less serotonin than cells with the more common gene
18
Q
Zhang et al. (2005)
A
- 87 depressed Ps
–> 9 patients with mutant form - 219 control group Ps
–> 3 people with mutant form - suggests that the mutant form led to less serotonin and thus higher chances of depression
- history of mental health, anxiety and alcoholism were found in the 3 mutant subjects in the control group
19
Q
issues with Zhang et al. (2005)
A
many clinically depressed Ps didn’t have the mutant form of the gene
20
Q
does short forms of the serotonin transporter protein always result in higher depression levels?
A
- no
- sometimes linked to depression and sometimes it isn’t
–> could be that psychological measures of depression are inaccurate
–> could be that the link doesn’t exist - solution: use brain scanners
21
Q
brain scanners and negativity
A
- use fMRI scanner
- ask people to judge angry and afraid faces
- look at response of amygdala
–> brain region that deals with emotions and memory - compare 2 groups
1. those with normal gene
2. those with 2 forms of the short gene - look at size of response (who responds more to negative emotions?)
–> likely to find higher brain activation to negative emotions in short form of the gene
22
Q
effects of the short form of the serotonin transporter gene
A
- makes the brain “over-respond” to negative emotions
- risk factor for depression?
–> but many people have short gene(s) and not depression? - NEED THE ENVIRONMENT
23
Q
Brown (1993) environment and depression
A
- 84% of depressed Ps had severed stress in the previous year
- only 32% in the control group has severe stress in the past year
24
Q
diathesis-stress model
A
- can have risk factor genes or NO risk factor genes
can have stress or NO stress - having risk factor genes AND stress is the only combination linked to depression
–> risk factor + stress = depressed patient
25
Q
Caspi et al. (2003)
A
- subjects from Dunedin multidisciplinary Health and development study
–> 1037 subjects
–> age 26 - measured stressful events
- divided subjects into groups based on forms of serotonin transporter gene
- measured depressive symptoms
26
Q
results of Caspi et al. (2003)
A
- no difference in number of stressful events between genetic groups
- depressive symptoms:
–> number of stress full life events = non-significant
–> genotype = non-significant
–> interaction of genes AND environment = highly significant
27
Q
Caspi study summary
A
- 5HT-T gene short (s) and long (l)
- more short forms you have more likely to be depressed
–> ss versus ls versus ll
–> BUT only when combined with stressful life events - gene x environment interaction
28
Q
Nicotine Acetylcholine Receptor α4 Subunit Gene
A
- ** smoking **
- addiction in general
- ADHD
- internet gaming in male Koreans
29
Q
GABRA2 – a GABA receptor (inhibitory)
A
- ** alcohol dependence**
- autism
- epilepsy
30
Q
DAT1 Gene – dopamine reuptake transporter
A
- cocaine addiction
- ADHD
- schizophrenia
- alcohol use
31
Q
comorbidity
A
- as gene variants are associated with lots of traits/diagnosis this could suggest comorbidity
- could be that a gene underlies lots of different disorders (common theme?)
