genetic similarity

• methods of research

  • kinship studies
  • twin studies
  • adoption studies
  • molecular genetics
• kinship studies

  looks at the concordance rate of behaviour within a family across several generations
• twin studies

  looks at the concordance rate of behaviour in MZ twins and DZ twins.
• adoption studies

  compare children with their biological mother and adoptive mother to measure concordance rate.
• molecular genetics

  based on using modern technology for genetic mapping and identifying the alleles of particular genes in a particular individual. Genetic variants are then correlated with observed behaviour.
• concordance rate

  the proportion of pairs of individuals that share a particular attribute, given that one of the individuals has that characteristic.
• Bouchard and McGue (aim)

  meta-analysis of IQ correlations between relatives.
• Bouchard and McGue (procedure)

  collate the data from 111 studies on IQ correlations between family relatives to gather information on concordance rates for IQ MZ twins raised together and apart, DZ twins raised together, siblings raised together and apart, parent and offspring raised together and apart and adopted parent and child.
• Bouchard and McGue (findings)

  apporximatly 70% of observed variation in the samples IQ could be attributed to genetic variation. Shows that a large proportion of a perons intelligence is based off of environmental factors.
• Bouchard and McGue (conclusion)

  intelligence is 54% inherited.
• Bouchard and McGue (strengths)

  • increased reliability - using multiple studies
• Bouchard and McGue (weaknesses)

  • generalisability - twins within study were self-volunteered.
  • correlational - cannot establish cause and effect relationship
• Hamer (aim)

  determine why cancers (e.g. Kaposi sarcoma) afflict unusually large numbers of homosexuals.
• Hamer( procedure)

  He begun by studying the family histories of 114 gay men and found more homosexual brother, uncles and cousins than expected. A follow up kinship study looked at DNA from 40 homosexual brothers, 33/40 shared genetic markers on the X chromosome, nothing like this was found n heterosexual men.
• Hamer (findings)

  concluded that the chromosome that it was found on is important for hetero and homosexual development and there are small differences within the gene of each group. However the finding doesn't explain homosexuality.
• Hamer (strength)

  • ethical benefits of genetic links to homosexuality - proves it is not 'a choice'
• Hamer (weaknesses)

  • replicability - mixed results have been found from follow-up studies
  • limited controls - other variables may have affected results.
  • small samples - 7/40 didn't conform to results, limits generalisability
• Bailey and Pillard (aim)

  to investigate the genetic basis of sexual orientation
• Bailey and Pillard (procedure)

  recruited MZ, DZ twins and adopted brothers through gay publications; all twins were raised together so have similar environmental factors. Sexual orientation of relatives was assessed indirectly or directly by asking questions. Questionnaires were used to ask participants an=bout childhood gender non-conformity.
• Bailey and Pillard (findings)

  52% of MZ twins were self-identified as homosexual.

  22% of DZ twins were self-identified as homosexual.

  11% of adopted brothers were self-identified as homosexual. Later study showed that result to be 9.2%.
• Bailey and Pillard (results)

  more closely genetically linked pairs were more likely to present homosexual or heterosexual tendencies.

  Researchers found that the level of childhood gender non-conformity did not predict results of homosexuality in any participants. (childhood gender non-conformity does not correlate with the development of homosexuality.)
• Bailey and Pillard (strengths)

  • confounding variables - gender non conformity, removes the variable
  • replicability - later study reinforces findings.
• Bailey and Pillard (weaknesses)

  • sample is not representative - female homosexuality, participants already had homosexual relative.
  • self reported data - assumed to be MZ twins but no proof
  • retrospective data - stereotypes could affect memories of childhood