Chromosome Breakdown Chromosomes Genes DNA Nucleotides With reference to relevant research studies, to what extent does genetic inheritance influence behavior? Gene Mapping • Some scientists are trying to determine the effect of a particular gene on behavior such as temperaments or psychological disorders. Caspi et al. (2003) The role of the 5-TT gene in depression after stressful events. • Longitudinal Study (vs Cross Sectional) • The 5-TT gene influences the level of serotonin, which is known to play a role in mood. Caspi et al. (2003) The role of the 5-TT gene in depression after stressful events. • There are two types of 5HTT genes. • Long- a little over 50% of population • Short- a little less than 50% • The researchers compared participants with normal 5-HTT (long) genes with shorter alleles. • Specifically after stressful events. Caspi et al. (2003) The role of the 5-TT gene in depression after stressful events. Results • After stressful events, the participants with the shorter 5-TT gene were more likely to become depressed. • The 5-TT gene could indicate vulnerability to depression. Caspi et al. (2003) The role of the 5-TT gene in depression after stressful events. Evaluation • Since so many people carry it (almost half the population), it is hard to say that in is the gene that made the difference. • Maybe it was the environmental factors (stressful events) that caused the depression. • Did not show a causeeffect relationship. Chromosomal Abnormalities • Gender comes from 23rd pair of chromosomes…men have XY…woman have XX. • Turner’s syndrome is single X. • Klinefelter’s syndrome is extra X…XXY • XYY- Super male Let’s take a better look at Twins…. • Monozygotic Twins (MZ or identical) come from the same sperm and egg and share 100% of there genes. • Dizygotic Twins (DZ or fraternal) come from two different eggs and share about 50% of their genes. • Regular siblings also share around 50% of their genes. Twins In twin studies, researches focus on something called a concordance rate… • The probability that if one individual has the trait the other will also have it. • It tells us if a trait is inherited. Schizophrenia Fraternal Twins: 15% Identical Twins: 50% • Usually in twin studies, one twin acts as a control for the other twin. • In good twin research sets of MZ are compared to sets of DZ for a trait of disorder. • High concordance rates with MZ and lower with DZ indicates the trait is due to genes (inherited). • Differences within pairs of MZ are thought to be environmental factors. Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence • This study used a selfselected sample of MZ twins who had been reared together (MZT) and MZ twins who had been reared apart (MZA). • Looked at a lot of factors but we will focus on intelligence. Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence Results: • Used the WAIS to measure intelligence. • The concordance rates for MZA was 69%, for MZT it was 88%. Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence • The researchers concluded that environmental factors do play a role in development of intelligence but IQ is to a large extent inherited. • 70% of the observed variation in the sample could be attributed to genetic variation. Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence • They claim that in their sample (white, middle class, industrialized nation) genetic inheritance in IQ accounts for around 2/3 of observed variance of IQ. • They also said that their findings do not indicate that IQ cannot be increased by environmental factors. Bouchard et al. (1990) Twin study investigating genetic inheritance in intelligence Evaluation • Correlational data cannot establish cause/effect relationships. • Concordance rates were high, but far from 100%. • No control for the effect of environmental variables. • Self-selected sample.