What are the assumptions of the Biological Approach?
Genetic determinism, biological basis of behavior, and the influence of evolution.
What is the biological Approach?
explanation of our behaviours mainly in terms of biological factors
How long has the biological study of the brain and behaviour been going on?
In parallel with the history of experimental psychology
Understanding Genetics
The body is made up of cells and each cell contains 23 pairs of chromosomes
What does DNA stand for?
Deoxyribonucleic acid
What is DNA?
the substance that chromosomes are made of
a chain of two or more nucleotides joined together
each cell in your body has the exact same DNA
What is a gene?
A gene is a segment of DNA that contains the production of one specific protein.
control our physical traits
Animals of the same species broadly have the same set of genes, and different species have different sets of genes.
What do we call different versions of a gene?
Alleles
if there is different versions of a gene (alleles) we say there is genetic variation in that characteristic e.g. hair colour.
what are sex cells?
either a sperm or egg
have 23 chromosomes
What occurs in reproduction?
Where a males sex cell (sperm) meets a women's sex cell (eggs) to form a new cell that has 46 chromosomes
what is genetic inheritance?
when traits are passed down from parent to child
what is a genotype?
A description of all of the genes and alleles in a body
what is a phenotype?
The observable characteristics or behaviours of a person (physical traits)
Genotype + environment = phenotype
What do we call Environmental factors?
things in the environment can affect our physical traits e.g. sun
behaviours and psychological traits are partly inherited
To sum up, the biological approach studies the extent to which behaviours are determined by genetics and genes determine behaviour by affecting processes inside the brain.
Environmental factors have a bigger impact on behaviour than they do on physical traits
What are the two types of twin?
MZ / Mono-zygotic (same genotypes, 100%)
DZ / Di-zygotic (different genotypes, 50%)
What type of twins are Monozygotic?
identical twins
What type of twins are dizygotic?
un-identical twins
Monozygotic twins come from one Zygote, which splits into two identical zygotes, whereas dizygotic twins come from two different zygotes.
Both monozygotic and dizygotic twins have some shared and some non-shared environments
The concordancerate is how often we see a trait or disorder within a group of people who share genes compared with those who do not share genes.
Concordance rates for MZ twins tend to be higher than for DZ twins because they share more genetic material.
Assumptions
Both MZ and DZ have a similar amount of shared environment
Shared environment has a similar impact on phenotype
What is a shared environment?
the environment that a pair of twins share in common.
what is a non-shared environment?
the environment that a pair of twins don't share in common.
what do we say for twins that have the same phenotype?
concordant
In twin study's, we don't include sets of twins where neither twin has the trait we're studying.
what is the concordance rate?
The percentage of twins who share a characteristic, given that at least one twin has the characteristic.
Genetic variation contributes to a trait if....
the concordance rate for monozygotic twins is bigger that the concordance rate for dizogotic twins
The bigger the difference in concordance rates between monozygotic and dizygotic twins, the more influence genetic variation has on the trait.
In 1996, McGuffin performed a twin study on the presence of depression in twins
McGuffin found that if one monozygotic twin had major depression, there was a 46% chance the other twin had depression too. They had a concordance rate of 46%.
For Dizygotic twins, McGuffin found that if one twin had major depression, there was a 20% chance that the other twin did too, having a concordance rate of 20%
McGuffin could conclude genetic variation does contribute to depression because the concordance rate was bigger for monozygotic (46%) than dizygotic (20%) twins.