Week 4 Flashcards
Dmitri K. Belyaev and the foxes
Russian silver foxes Select only for tameness 40 Generations later … Tame Eager to hang out with humans, whimpered to attract attention, and sniffed and licked their caretakers. They wagged their tails when they were happy or excited. Also … Floppy ears, short or curly tails, extended reproductive seasons, changes in fur coloration, changes in the shape of their skulls, jaws, and teeth, lost their "musky” fox smell.
Biology of Behaviour
First Dichotomy
Physiological or psychological?
Nothing in Psychology Makes
Sense Except in the Light of
Evolution
• Cartesian dualism – 2 types of stuff
• Physical matter which obeys the laws of nature (body)
• Mind which controls behaviour – separate, not physical, no
natural laws (soul, self, spirit)
• Now – mostly behaviour has a physiological basis (brain)
• Damage or stimulation to parts of the brain can produce
complex psychological changes
• Some nonhuman species now shown to possess abilities
once considered purely human “mind” stuff
• But … still many feel that some aspect of being human
transcends the physical brain
Biology of Behaviour
Second Dichotomy
Nature or Nurture?
Nothing in Psychology Makes
Sense Except in the Light of
Evolution
• Nurture – John Watson
• “Give me a dozen healthy infants, well-formed, and my
own specified world to bring them up in and I’ll
guarantee to take any one at random and train him to
become any type of specialist I might select—doctor,
lawyer, artist, merchant-chief and, yes, even beggar-man
and thief, regardless of his talents, penchants,
tendencies, abilities, vocations, and race of his
ancestors. (1930)”
• Nature – instinctive behaviours
• Flawed question - interactions
Interactions
Nature Genes drive neural development Nurture Environment influences neural development • Environment modifies gene expression – epigenetics • Behaviour driven by the current situation • Experience depends on behaviour • Most adaptive behaviours succeed influencing the gene pool of subsequent generations
Nature
Genes drive neural
development
Nurture
Environment
influences neural
development
What is the biology of behaviour?
Behaviour is physiological – a biological trait
Current behaviour from complex interactions:
• Genes
• Development
• Past environment (evolution)
• Past experience (genes and function)
• Current environment
Mendelian Genetics
• Offspring share traits with parents – how are these traits passed on?
• Experiments on peas - quantitative experiments not just breeding
• Looked at dichotomous traits (2 versions – round/wrinkled pea;
green/yellow pea; purple/white flower; standard/dwarf plant)
• First establish true breeding varieties – plants that only produce
progeny like themselves when allowed to self pollinate –> P1
generation
• Then breed parents with different traits –> F1 generation
• Then crossbreed F1 –> F2 generation
• Transmission genetics – statistical rules governing transmission of
hereditary elements one gen to next
• Parents true
breeding
• F1 only 1
kind
• F2 mixed in 3
to 1 ratio
How Mendelian genetics work - seed example
• Two factors account for the inheritance of dichotomous traits – e.g.
a brown seed factor and a white seed factor (i.e. genes - different
versions are referred to as alleles)
• One allele (Dominant) dominates the other (Recessive)
• An organism receives (at random) one gene from each parent
• Genotype – the genetic makeup (e.g. 1 brown gene and one white
gene)
• Phenotype – the expressed or observable trait (e.g. brown seeds –
which could be either brown/white genotype or brown/brown)
Molecular Genetics
• Mendel’s “factors” are genes – lengths of DNA that code for proteins • Genes reside on chromosomes – long lengths of DNA that contain many genes (and other stuff – promoters, enhancers, inhibitors) • Chromosomes come in pairs (and therefore so do genes) • Humans – 23 pairs – 1 pair from each parent • 22 pairs are autosomal chromosomes • 1 pair sex chromosomes (XX=F; XY=M)
How molecular genetics work
Replication- DNA Polymerase (DNA->DNA) Transcription- RNA Polymerase (DNA->RNA) Translation- Ribosome (RNA-> Protein) Central Dogma • Flow of genetic information • The version of a gene (allele) determines the form of the protein • Proteins may be structural elements, enzymes, signalling elements • Proteins • Early neural development • Synapse formation and maintenance • NT manufacture • NT receptors • NT transporters • Brain expresses more genes than any other organ • Within the brain, different cell populations express different groups of genes
Mutation and Variation
First source of variation – different functioning alleles in the population • During replication things can go wrong • Small changes – SNPs – single base pair change • More complex changes – small or large deletions or additions • Whole genome duplications • Sometimes fatal • Sometimes produces slightly modified proteins • Sometimes produces extra genes that are free to evolve further
The steps in Meiosis and
During meiosis, pairs of similar chromosomes line up parallel to each other.
Then, the replicate their genetic material.
Next, one chromosome crosses over the other.
The crossed-over chromosomes break apart at the crossover.
Crossing over shuffles the genetic material; it is why all the genes on a chromosome are not always inherited together.
Nature versus Nurture
• Many traits (phenotypes) are polygenic (exceptions e.g. Huntington’s
Disease)
• Especially true for complex traits like intelligence or personality
• Many genotypes influence the likelihood of a particular phenotype –
typically not all or none (exceptions e.g. Huntington’s, Down
Syndrome)
• Often interested more in the genetics underlying variations in a trait
rather than the trait itself (e.g. intelligence)
• Heritability is a statistic
Heritability
• Estimate of the proportion of variability in a given study on a particular trait
as a result of genetic variation across individuals in that study
• Heritability estimates tell us about the contribution of genetic differences
to phenotypic differences among participants
• It does not tell us anything about the relative contribution of genes and
environment/experience to the development of individuals
• In a sample with low environmental variation, contribution of genetic
variation may be over-estimated (e.g. upper-middle class American
households are environmentally very similar)
• In Western samples, complex psychological traits all have heritability
estimates somewhere between 40% and 80% percent.
Twin Studies
The main tool for assessing the relative contributions of genetics and
environment on psychological traits has been to study monozygotic and
dizygotic twins.
Minnesota Study of Twins Reared Apart
• 59 pairs of monozygotic twins (100% genes shared)
• 47 pairs of dizygotic twins (on average 50% genes shared)
• Ages from 19 - 68
• 50 hours of testing on each participant (including personality, interests, and
attitudes)
Results:
• MZ twins were more similar on all psychological dimensions than DZ twins
• Regardless of whether they were raised in the same or different household
Jim Twins
• MZ twins adopted at the age of four weeks
• Both of the adopting couples named their son James
• Both married to Bettys and divorced from Lindas
• One named first son James Alan, the other named first son James Allan
• Both twins have an adopted brother whose name is Larry
• Both named their pet dog “Toy”
• Both had law-enforcement training and been a part-time deputy sheriff
• Each did poorly in spelling and well in math
• Each did carpentry, mechanical drawing, and block lettering
• Each vacation in Florida in the same three-block-long beach area
• Both twins began suffering from tension headaches at eighteen, gained ten
pounds at the same time, and are six feet tall and 180 pounds
Down Syndrome
• Trisomy 21 – extra copy of chromosome 21
• A genetic condition but outcomes depend on environment
• Intellectual disability – level varies
• DSCAM – a gene on chromosome 21 that encodes a signalling
molecule (Down Syndrome Cell Adhesion Molecule)
• Expressed in the developing nervous system – over-expressed in DS
• Developing neurons – axons need to find the right target
• DSCAMs facilitate attraction/repulsion
• Influences nervous system development
