Genes and Behaviour

Question 1

GENES & BEHAVIOUR

Answer 1

• genes produce proteins NOT beh
• BUT can influence beh via effects of proteins on neurons/hormones/brains/muscles
• resulting beh affected by environmental conditions where it develops (gene x environment interaction)
• expressed beh depends on said interactions
• genes influence learning mechanisms
• beh flexibility = key feature of most organisms

Question 2

GENES

Answer 2

• located on chromosomes (DNA coiled around histones) located in cell nucleus
• gene expression = transcription (DNA -> RNA) + translation (RNA -> protein)
• produce proteins (large complex molecules; do most cell work)
• genotype = entire gene set an individual prossesses
• phenotype = observable characteristics of individual influenced by genes x environment
• OMIM (Online Mendelian Inheritance in Man) = large searchable up to date database of human genes/traits

Question 3

PROTEINS

Answer 3

primary structure (amino acid) -> secondary structure (a-helixes) -> tertiary structure (polypeptide chains) -> quatemary structure (protein molecule complex)
- include: antibodies/enxymes/hormones/structural components/transport/storage

Question 4

ALLELES & GENETIC DIVERSITY

Answer 4

• individuals have 1/2 alleles (variants) of gene BUT multiple alleles can exist in pop
• 74% = human eye colour variance (ie. dominant brown over blue = brown eyes)
  AGOUTI GENE
• involved in coat pattern/shading of mammals
• when upregulated hair follicle melanocytes switch from making black -> yellow pigment
• lethal alleles lead to death of homozygous recessive offspring

Question 5

POLYGENIC INHERITANCE

Answer 5

• quantitative traits often show polygenic inheritance (influenced by many genes each w/small effect) ie: height/skin/educational attainment/sex orientation

Question 6

EXTENT OF BEHAVIOUR TRANSMITTED BY GENES

Answer 6

SOKOLOWSKI (2001)

• challenges of beh genetics research
• difficulty in defining/quantifying beh
• environmental influences beh
• within/between individual beh variation
• involvement of many genes
• dif genes function in dif tissues at dif times during organism development

Question 7

PEROMYSCUS MICE BURROW STRUCTURE

Answer 7

WEBER et al (2013)

• deer mouse = grassy habitat/no escape tunnel
• oldfield mouse = open habitat/escape tunnel
• captive-reared mice placed in sand-filled arenas for first time; build species-typical burrows
• F1 offspring (deer x oldfield) = 100% escape tunnels
• backcrossed (F1 x deer) = 50% escape tunnels
• single dominant locus controls escape tunnel building

Question 8

FRUIT FLY LARVAE FORAGING

Answer 8

DE BELLE & SOKOLOWSKI (1987)

• sitters or rovers
• both beh types = wild-type phenotypes (70% rovers; 30% sitters in natural pop)
• female sitter x male rover = same phenotype (rover)
• female F1 x male F1 = 3:1 phenotypic ratio
• single gene influences beh expression BUT doesn’t encode it

Question 9

FRUIT FLY LARVAE FORAGING +

Answer 9

DE BELLE et al (1989)

• FOR gene encodes kinase G protein; affects neuronal activity (STM/LTM)
• sitters homozygous for recessive allele FOR^S
• rovers have at least 1 dominant allele FOR^6 copy

Question 10

MATERNAL MICE BEHAVIOUR

Answer 10

• fosB mice mutation causes maternal beh disruption ie. creating nest/cleaning pups/retrieving pups to nest/crouching for warmth/nursing
• single gene can determine phenotypic complex beh expression
• fosB products widely expressed in brain; mainly in preoptic hypothalamus area (critical for nurturing beh)
• fosB-deficient mice = normal motor beh/reproductive hormones/intact glands (ie. specific mutation effect)

Question 11

GENES X PHENOTYPES

Answer 11

• gene expression acts at dif phenotypic levels
• environmental influences act on gene expression/phenotype
• gene expression can influence:
  1. other gene expression
  2. cell/tissue/organ activity
  3. developmental processes
  4. brain/muscles/messenger systems activity -> beh expression

Question 12

PHENOTYPIC VARIANCE

Answer 12

• total phenotypic variance (VT) in trait based on genetic variance (VG) additive effects/environmental variance (VE); VT = VG + VE
• trait heritability ((h^2) = VG/VT) = phenotypic variance proportion associated w/genetic variance
• N.B. heritable ISN’T “genetically determined” (ie. height highly heritable in time of plenty; less in famine)
• response to selection (R = h^2 x S)

Question 13

SELECTIVE BREEDING

Answer 13

• artificial selection = mice selected for dif nest building levels/rate for maze-running ability
• genotype effects can be masked by environmental effects; enriched environment improved performance of maze-dull rats
• restricted environments prevented inherited ability expression

Question 14

GENETIC MUTATION

Answer 14

• most harmful/neutral in effects; rarely beneficial
• wild-type = >1% frequency alleles
• mutant = <1% frequency alleles
• monomorphic = gene w/1 wild-type allele
• polymorphic = gene w/>1 wild-type allele
• knockout = lab strain where known mutation inactivates/knocks out gene’s normal function

Question 15

GENETIC MUTATION TYPES

Answer 15

GERM-LINE
- germ-line mutation
- entire organism carries mutation 
- half of gametes carry mutation
SOMATIC
- gametes 
- somatic mutation to embryo
- patch of affected area on organism
- no gametes carry mutation

Question 16

DNA BASES

Answer 16

NUCLEOTIDES

• adenine
• guanine
• thymine
• cytosine

Question 17

GENETIC MUTATION X RADIATION

Answer 17

• mutagens/radiation increase mutation rate ^ spontaneous level
• intercalating agents cause single-nucleotide insertions/deletions
• ie. social amnesia related to single gene mutation

Question 18

TWIN STUDIES

Answer 18

• twin/adoption studies investigate genetic/environmental influences on human beh/cog
  MONOZYGOTIC/IDENTICAL
• genetically identical
• shared pre/post-natal rearing environment
  DIZYGOTIC/NON-IDENTICAL
• genetically dif
• shared pre/post-natal rearing environment
  ADOPTED
• genetically dif
• dif pre-natal rearing environment
• shared post-natal rearing environment

Question 19

TWIN STUDIES CORRELATIONS

Answer 19

• strong/+ correlation -> important genetic component
• weak correlation -> genetic component unimportant
• E = variance resulting from non-shared environment/errors of measurement
• C = variance due to shared environment
• A = additive genetic variance/heritability (ie. effect if you substitute 1 allele for another)

Question 20

TWIN STUDIES LIMITS

Answer 20

• heritability estimates AREN’T comparable across environmental contexts (ie. IQ linked to genetic variance in wealthy families to environmental variance in poor families)
• biased sampling across dif family situations -> confounding factors (ie. adoptions rare in low-income families)
• comparisons don’t clearly separate genetic/environmental effects (ie. monozygotic twins share environment > dizygotic)

Question 21

SUMMARY

Answer 21

• gene = DNA region encoding protein production (coding + regulatory regions)
• genes affect beh via effects on neurons/hormones/brains/muscles
• to understand genetic beh basis, we need to understand not only single gene expression but also its regulation/other gene interaction
• heritability = phenotypic variance proportion associated w/genetic variance; doesn’t indicate degree to which trait is “genetically determined”
• genetic effects on beh evidence:
  1. beh difs maintained under common rearing conditions (ie. Peromyscus mice)
  2. mendelian phenotypic ratios under cross-breeding (ie. rover/sitter fruit flies)
  3. individuals carrying known mutations behave dif (ie. fosB/Oxt^-1-)
  4. beh divergence in selectively bred lines (ie. nest building)
  5. genetic relatives/non-relatives comparison reared together/apart (ie. twin/adoption studies)