behavioural genetics 2

Question 1

Mendel (1822-1884)

Answer 1

• 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)

Question 2

Mendel’s pea pods summary

Answer 2

• 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)

Question 3

phenotype

Answer 3

• physical manifestation of the genotype
• trait/characteristic
  –> e.g. blue eyes

Question 4

genotype

Answer 4

the genetic material

Question 5

allele

Answer 5

different forms of a gene that control the same trait
–> e.g. G vs y

Question 6

heterozygous

Answer 6

• one dominant allele and one recessive allele
  –> e.g. Gg

Question 7

homozygous

Answer 7

• same type of allele
• two dominant or two recessive
• e.g. GG or yy

Question 8

Dominant and recessive

Answer 8

• dominant = capital letter (G)
• recessive = lower case letter (g)
  –> recessive need two alleles to present the characteristic

Question 9

gene for serotonin transporter

Answer 9

• 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

Question 10

forms of serotonin transporter

Answer 10

• short form (s) associated with higher incident rate of depression

Question 11

additive genes?

Answer 11

• 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

Question 12

additive genes and the variance equation

Answer 12

• Vp = A squared + C squared + E squared
• A is the ADDIDITVE genetic component

Question 13

why two alleles in a genotype?

Answer 13

• alleles refer to chromosomes
• chromosomes come in pairs
• autosomes = all other traits, practically identical (22 pairs)
• allosomes = sex chromosome (XX or XY)

Question 14

chromosomes and DNA

Answer 14

• 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)

Question 15

what does DNA do?

Answer 15

1. replicates
   - double helix (2 strands) unwind
   - exposed pairs line up with each strand
   - 2 new complementary strands form
2. 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

Question 16

RNA recap

Answer 16

• ribose
• uracil not thymine
• base pairs = AU, GC

Question 17

the Tryptophan Hydroxylase gene (+ mutations)

Answer 17

• 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

Question 18

Zhang et al. (2005)

Answer 18

• 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

Question 19

issues with Zhang et al. (2005)

Answer 19

many clinically depressed Ps didn’t have the mutant form of the gene

Question 20

does short forms of the serotonin transporter protein always result in higher depression levels?

Answer 20

• 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

Question 21

brain scanners and negativity

Answer 21

• 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

Question 22

effects of the short form of the serotonin transporter gene

Answer 22

• 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

Question 23

Brown (1993) environment and depression

Answer 23

• 84% of depressed Ps had severed stress in the previous year
• only 32% in the control group has severe stress in the past year

Question 24

diathesis-stress model

Answer 24

• 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

Question 25

Caspi et al. (2003)

Answer 25

• 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

Question 26

results of Caspi et al. (2003)

Answer 26

• 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

Question 27

Caspi study summary

Answer 27

• 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

Question 28

Nicotine Acetylcholine Receptor α4 Subunit Gene

Answer 28

• ** smoking **
• addiction in general
• ADHD
• internet gaming in male Koreans

Question 29

GABRA2 – a GABA receptor (inhibitory)

Answer 29

• ** alcohol dependence**
• autism
• epilepsy

Question 30

DAT1 Gene – dopamine reuptake transporter

Answer 30

• cocaine addiction
• ADHD
• schizophrenia
• alcohol use

Question 31

comorbidity

Answer 31

• 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?)