PSYC 1100 Section 2.1 Genetics & Environment

philosophical debate about the relative importance of inborn characteristics vs. experience

• - Kant
• - believed that innate or inborn mechanisms were the basis of knowledge and other important charateristics

• Locke and Hume
• believed that sensory experience was the basis of knowledge and other important characteristics 
• - 'tabula rasa' i.e. 'blank state'
• - learn by association, e.g. Law of temporal contiguity

False dichotomy: because for most psychological characteristics both genetic and environmental factor contribute

• Genetic code: information for protein synthesis (amino acid sequence) contained in the sequence of nitrogen-containing bases in the structure of DNA
• DNA=>mRNA=>tRNA=>proteins
• Genotype vs. Phenotype:
• - genotype: genetic makeup of organisms, encoded in DNA
• - phenotype: the expressed traits of an organism, is a product of genetic/environment interaction during every stage of development
• -Behavioral characteristics are PHENOTYPES, not genotypes
• -The genotypes associated with various behavioral phenotypes can either be located on a single gene locus or multiple gen loci (i.e. poly genetic)
• -The vast majority of behavioral traits appear to be influenced by polygenetic coding
• Twin Studies: look at
• - concordance (degree of agreement in characteristics between twins)
• - correlation (degree and direction of linear relation between variables)

• Concordance - if one twin is schizophrenic, what is the probability that the other one is schizophrenic?
• Degree of identical twins reared apart:
• 15-40% depending upon the study
• Frequency of schizophrenia in general population: 1%
• There is a genetic predisposition towards schizophrenia

• Correlation can be expressed by coefficient r
• r values can vary between -1.0 and +1.0
• Correlation coefficients capture how closely the relation between two variables follows a straight line
• -  the sign of the correlation (+ or -) is related to the slope of the line
• - the absolute value is related to how closely the data resemble a line
• -  if the r value is nearer to 0, it means no relation, while absolute value is nearer to 1.0 reflect a stronger linear relation 
• - an r value of -1.0 or +1.0 reflect a perfect relation between the variables

• Most correlational studies with identical twins raised apart show IQ correlation about r=0.7
• The correlation squared (r^2) is equal to the proportion of variability in one set of IQs accounted for by variability in the other sets of IQs.
• r^2=0.7^2=0.49
• There is about 50% of the variability in IQ is accounted for by genetic factors