The Biological Approach


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  • Created by: Hannah
  • Created on: 24-05-10 15:07


Identical share 100% of their genes- Monozygotic (Mz) twins

Fraternal/non-identical share 50% of their genes- Dizygotic (Dz)

Mz can be compared with Dz twins to see if they are more similar

If genes do control characteristics, Mz twins should be more similar than Dz twins.

Seperated twins

Can compare similarity of Mz twins who have grown up in the same or different environment.

If the twins are more alike despite being reared apart, supports nature argument.

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Seperated Twins

  • Loehin (1992) showed similarity in personality between Mzs reared together and apart

Evidence suggests schizophrenia is part inherited (Gottesman and Shields)

He concluded: Mzs have a higher probability of sharing schizophrenia than Dz twins

Therefore schizophrenia is partially a result of our genes. Not entirley because otherwise all Mz twins of suffrers would have it so there must be other factors such as disfunctional family Tienari (1992)

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Twins and the environment

  • Genes play a role in psychological characteristics but environmental factors are important
  • Seperating twins can help show this

Extraversion- how impulsive and sociable we are

Neuroticism- being anxious and moody

Although personality twins is less similar than those raised together, they are still more alike than we think

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Homosexuality and genes

  • X chromosome sometimes has a genetic marker associated with homosexuality
  • Hu et al (1995)- found genetic marker present in gay brothers not lesbian sisters. Gene in males not females

Suggests genetics only play part of a role in male's sexuality

Twin studies and homosexuality:

Bailey et al (2000)- found that concordance of homosexuality was less in male Mz twins than female Mz twins. Figures for Dz twins much lower suggesting gentic component to sexuality,

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Evaluation Twin Studies


  • Twins studies have generated a large volume of data with large sample sizes which makes studies more valid and credible
  • Twin studies are replicable so are more reliable
  • Lots of studies to support role of genes for example Gottesman and Shields
  • Twin studies suggest genetic components may be involved in a range of genetic phenomina e.g. sexuality, schizophrenia and smoking
  • Money study supports nature (genes) over nature as David Riemer always felt like a boy
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Evaluation Twin Studies


  • usefulness of data from twin studies relies on methods used to gather data ,such as IQ tests, being reliable and valid
  • Psychological variables are difficult to measure anyway
  • seperated twins may have been seperated at different ages, in a variety of circumstances and often not assessed for similarity until reunited
  • Twins may have experienced a similar environement despite being seperated therefore difficult to know if the similarites between twins are a result of genes or the environement
  • adults tend to treat Mzs more similary than Dzs as they look more alike so it may mean that a similar environment as well as identical DNA leads to the similarites between Mzs.
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