twin and adoption studies

• adoption studies compare the childs behaviour with both biological and adoptive parents
• if adopted children are similar to adoptive parents in particular behaviours it suggests role of the environment
• if an adoptive child is similar to their biological parents in a particular behaviour it suggests the role of genes
• mednick et al (1987) analysed all the court convictions between 1927 and 1947 in denmark and found over 14,000 adoptees, they investigated criminal convictions of both the adoptive and biological parents
• if biological and adoptive had no crim record 13.5% of adoptees had a crim record, if only biological have one its 20%, if just adoptive its 14.7, if both biological and adoptive have a crim record it is 24.5%
• mednick et al findings ?

  strong relationship between convicted biological parent and son committing a crime but it shows the greatest influence is both genetics and environment
• monozygote twins are identical, dizygote are unidentical
• identical twins are made by a single egg and single sperm and then splits in two
• fraternal twins are born from separate eggs fertilised from separate sperms
• concordance rate?

  the extent to which twins share the same characteristic
• twin studies ?

  compare identical and non identical twins, MZ twins share 100% of their genes, DZ twins share about 50% of their genes
• twins share 100% of the same environment with their twin pair in a twin study
• twin studies measure the number of twins in each sample that both posses the behaviour, the result is a concordance rate, the higher the number the more similar the twins are
• twin study evaluation?

  although mz concordance is higher its never 100%, although the biological parent-child similarity is higher than the adopted which suggests the importance of genetics, the strongest impact is environmental and genetic causes, this is explained by the diathesis stress model