Genes and behaviour Flashcards
what do genes produce?
proteins
how can genes influence behav through proteins?
neurons
hormones
brains
muscles
what do expressed behaviours depend on?
gene x env interactions
what do genes influence?
mechanisms for learning
what is a key feature of most living organisms?
behavioural flexibility
where are genes located?
on chromosomes (DNA coiled around histones) located in the cell nucleus
what does gene expression involve?
transcription
translation
what are proteins?
large, complex molecules that do most of the work in cells
examples of proteins
antibodies
enzymes
messengers - e.g. hormones
structural components - e.g. membrane channels, actin in muscles
transport/storage
how much of the vertebrate genome codes for proteins
1.5%
what is the relationship between amount of chromosomal DNA and organism’s complexity?
no consistent r’ship
what amount of DNA do 2 humans share?
99.8%
how much of their DNA do humans share with chimpanzees?
98%
what % of DNA do humans share with mice?
92%
genotype
the set of genes an individual possesses
phenotype
the observable characteristics of an individual, influenced by genes and environment
alleles
Individuals have one or two alleles (variants) of a gene, but multiple alleles can exist in the population
e.g. eye colour
agouti gene
involved in coat pattern and shading of mammals
when upregulated, hair follicle melanocytes switch from making black to yellow pigment
lethal alleles
lead to death of homozygous recessive offspring
Homozygous yellow-coated mice die as embryos
polygenic inheritance
(multi-gene) inheritance of human skin colour
additive genetic variance
alleles A, B, Cdominant, dark pigmentation (more melanin)
alleles a, b, crecessive, light pigmentation (less melanin)
each parent produces eight different types of gametes
these combine with each other in 64 different ways
results in a total of seven skin colours
challenges of behavioural genetic research - Sokolowski (2001)
difficulty in defining and quantifying behaviour
environmental influences on behaviour
within- and between-individual variation in behaviour
involvement of many genes
different genes function in different tissues at different times during the development of an organism
burrow structure in Peromyscus mice
Deer mouse (P. maniculatus)
- lives in grassy/forest habitat
- builds burrows with short entrance tunnel and no escape tunnel
Oldfield mouse (P. polionotus)
- lives in open habitats (beaches, fields)
- builds burrows with long entrance tunnel and escape tunnel
burrow structure in Peromyscus mice - Weber et al. (2013)
Captive-reared mice placed in sand-filled arena for first time
- builds species-typical burrow
F1 offspring of maniculatus × polionotus hybrid
- 100% escape tunnels
Backcrossed F1 × maniculatus
- ~50% escape tunnels
single, dominant locus controls building of escape tunnel
foraging in fruit-fly larvae
Both behavioural types are wild-type phenotypes (70% rovers, 30% sitters in natural populations)
F1 offspring of female sitter x male rover
- essentially all same phenotype (rover)
F2 offspring of female F1 x male F1
- 3:1 phenotypic ratio
single gene influences expression of behaviour (but does not encode it)
foraging in fruit-fly larvae - da Belle et al. (1989)
for gene encodes protein kinase G, which affects neuronal activity (short- and long-term memory)
sitters homozygous for recessive allele forS
rovers have at least one copy of dominant allele forR
maternal behaviour in mice
fosB mutation in mice causes disruption of maternal behaviour: creating a nest, cleaning the pups, retrieving them to the nest, crouching over them for warmth and nursing
Single gene can determine phenotypic expression of complex behaviour
- fosB gene products widely expressed in brain, but mainly in preoptic area of hypothalamus (critical for nurturing behaviour)
- fosB-deficient mice: normal motor behaviour, normal levels of reproductive hormones and intact glands—not a pleiotropic effect
where does gene expression act?
at 3 diff phenotypic levels
what can expression of a gene influence?
expression of other genes
activity of the cell, other tissues and organs
developmental processes
activity of brain, muscles, messenger systems→ expression of behaviour
what do env influences act on?
gene expression and/ on phenotype
what are traits determined by?
genes and env in conjunction - continuous variation
what can quan traits be?
morphological
physiological
behavioural
norm of reaction
Pattern of phenotypic expression of a single genotype across a range of environments
what is total phenotypic variance (VT) in a trait based on?
additive effects of genetic variance (VG)
environmental variance (VE)
VT = VG + VE
trait heritability
h2 = VG / VT
proportion of phenotypic
variance associated with genetic variance
N.B. heritable ≠ ‘genetically determined’
artificial selection of heritable traits
h2 = R/S
h2 = 0 (no resemblance)
h2 = 1 (full resemblance)
artificial selection: rats selected for maze-running ability
Effects of genotype can be masked by environmental effects
enriched environment improved performance of maze-dull rats
restricted environments prevented expression of inherited ability
genetic mutation
Most mutations are harmful or neutral in their effects; only rarely are mutations beneficial
Alleles at >1% frequency termed wild-type
Alleles at <1% frequency
termed mutant
Gene with one wild-type allele is monomorphic
Gene with >1 wild-type allele is polymorphic
germ-line = whole body - gametes carry mutation
somatic = certain area - gametes don’t carry mutation
what increases mutation rate above spontaneous level?
mutagens and radiation
examples of mutagens and radiation
Oxidative radicals
Intercalating agents cause single-nucleotide insertions/deletions
shorter wavelength (high-energy) radiation capable of inducing mutations in DNA
example of genetic mutation
social amnesia is related to mutation in single gene
Oxt−/− males cannot produce oxytocin
- continue acting same way towards female even when already met her
identical twins
monozygotic
Genetically identical
Shared same early (pre-natal) rearing environment
Shared same late (post-natal) rearing environment
non-identical twins
dizygotic
Genetically different
Shared same early (pre-natal) rearing environment
Shared same late (post-natal) rearing environment
adopted children
Genetically different
Different early (pre-natal) rearing environment
Shared same late (post-natal) rearing environment
nature v nurture
Genetic factors contribute to individual differences in general cognitive abilities
A = additive genetic variance, heritability (i.e. effect if you substitute one allele for another) - plays biggest role
