Genetic similarities

Genetic similarities - the proportion of genes or DNA that is shared between populations.

• 99.9% genetically similar to someone we are not related to, 96% to chimpanzees, 60% to a banana and 90% to a cat.

• By looking at people or animals that share high proportions of DNA with us we can understand the potential role of the gene on our behaviour.

• If you share a higher proportion of genetics and you do the same behaviour - it is mare likely to have a genetic root.

• Parents and siblings 50% concordance rate (CR), grandparents 25% CR, niece/nephew 25% CR and cousin 12.5% CR.

TWIN STUDIES:

• Twin studies - conducted on identical and fraternal twins to understand the importance of genetic and environmental impacts.

• Monozygotic twins (MZ) : identical 100% genetically identical twins

• Dizygotic twins (DZ): fraternal, 50%

• Should be the case that the higher the genetic relationship, the more similar individuals will be if particular characteristics being investigated is inherited called concordance rate.

• CR - the % of cases in which both members of a pair have a particular attribute. MZ (100%) higher CR than DZ (50%) if behaviour is genetic.

FAMILY STUDIES:

• Family studies - studies done across generations between members of a family to understand role of genetics.

• Child inherits 50% mum 50% dad

• Brothers/sisters 50%

• Grandparents 25%

• Cousins 12.5%

• Different degrees of genetic relatedness are compared with respect to specific traits of behaviour. Therefore CR should be higher with mum and dad than from cousin.

• For example high IQ child must = high IQ parents

ADOPTION STUDIES:

• Adoption studies - studies to compare the role of genetics and the environment.

• Allows the most direct comparison of genetic and environmental influences of behaviour.

• Adopted children generally share none of their genes with their adoptive parents but they do share 50% with their biological parents.

• It would be reasonable to suppose , therefore, that if the heritability of a behaviour is high and the environment has little part to play , then the behaviour of adopted children should correlate more strongly with the behaviour of their biological parents than their adoptive parents.

• If it is the other way around, the environment has the strongest role to play.

COCCARO ET AL (1997) - twin studies

Aim: IV: MZ or DZ years DV: level of aggression and type of aggression RM: quasi + survey

• Subjects for the MZ and DZ twin pairs recruited from the Vietnam Era Twin (VET) registry.

• Consists 7375 (target pop) born between 1939 and 1955. Surveys sent, 796 responded, 628 took part.

• Burk and Durkee hostility scale (BDHI) is a 75 item paper and personal questionnaire designed to assess different types of hostile behaviour - direct assault, indirect assault, verbal assault, and irritability.

• The MZ twin pairs were found to have a 50% CR whilst DZ twins were only 19%.

Ethics:

• Met consent - volunteered

• Met right to withdraw

• Not met protection from harm - they are war veterans/ could have PTSD, potential emotional harm.

BELYAEV (1969)

Aim: IV: genetic inheritance DV: tameness RM: lab + observation

• 30 male foxes and 100 vixens (130)

• Selected foxes for tameness not more than 4-5% of male offspring and about 20% of female offspring have been allowed to breed.

• To ensure that their tameness results from genetic selection, foxes were not trained. Most of them spend their lives in cages and are allowed to be

HUTCHINGS AND MEDNICK (1975)

Aim: IV: adopted vs biological father DV: criminality RM: quasi

• The researchers decided to look at the level of genetic similarity in adopted children who had biological parents with criminal convictions and likelihood of further gens committing criminal acts in future gens.

• Look at 14,000 adopted children

• If both the biological and the adoptive fathers in Denmark had criminal records, then 36% of the sons also had a criminal record.

• If the biological father was the only one who had criminal record, the rate of a child also having a criminal record dropped to 11%. Where neither had criminal records than the likelihood was 10%.

• Overall, the results suggest that the closer the level of genetic similarity between male criminals, the more likely future male generations were to be involved in criminal records.