Genes Flashcards
Genotype
The genes an organism has inherited
How many genes does an organism inherit from each parent?
23
23 genes into chromosomes
46 chromosomes
Phenotype
The traits that are actually expressed
Examples of a physical phenotype:
Eye colour
Examples of non physical phenotype:
Temperament
Depression
Whether the gene is expressed or not depends on two different things:
- the interaction of the gene with other genes (dominant or recessive)
- the interaction between the genotype and the environment
Dominant allele
[Written as a capital letter]
If a dominant allele is inherited from either parent, the particular characteristic will always be expressed in the phenotype.
Recessive allele
[Written as a lowercase letter]
Will only be expressed in the phenotype if inherited from both parents.
What is the interaction between genes and the environment:
- psychological disorders
- stress diathesis model
Development of disorder=
Combination of diathesis factors (genetic vulnerability) and stress factors (environmental triggers)
- one factor alone can’t cause behaviour
Method of investigating influence of genes
Twin study
What twin studies do:
Investigate many pairs of twins and assess how often they share a particular characteristic
Concordance rate
The likelihood that 2 individuals share the same characteristic
Monozygotic twins
Identical
Share 100% of their DNA
Dizygotic twins
Non identical
Share 50% of their DNA
If a characteristic is purely genetic:
Concordance rate for MZ twins 100%
Concordance rate for DZ twins 50%
If the concordance rate is significantly higher for MZ twins than DZ:
The behavioural characteristics are mainly genetic
- increases the likelihood of the twins sharing a behaviour
If concordance rate for MZ and DZ is similar:
The characteristic is determined by the environment
Golden rule of twin studies:
As the proportion of shared genes increases, so does the likelihood of both twins demonstrating the same behaviour
The concordance rate is proportionally acceptable only if it is
Double or more
