genetic theories Flashcards
(29 cards)
What type of theories are genetic theories?
Biological
What are the three genetic theories?
Twin studied, adoption studied and Jacob’s XYY syndrome
What did the Twin studies suggest?
a heritable trait may increase the risk of criminal behaviour
what is a monozygotic twin?
identical twins - from 1 egg - share 100% of DNA
what is a dizygotic twin?
non-identical twins - from 2 eggs - share 50% of DNA
what is concordance rate?
when twins share characteristics or act in a similar way
What did Johannes Lang (1929) study show?
10/13 MZ twins had served time - 2/17 DZ twins served time
what did Christiansen (1977)
criminality CR for MZ twins was 35% and only 13% for DZ
a biological relationship between MZ twins is..
a naturally occurring variable
who found a higher CR for identical twin than non-identical?
Ishikawa & Raine
why is Twin studied unreliable?
if genes were the only cause of criminality, there would be a 100% CR when one of the twins offends
why is it impossible to isolate biological and environmental factors?
twins may share the same genes but not the same home, life or school opportunities
Why was early twin studies, such as Lang (1929) not reliable?
DNA didn’t exist - they went purely based off appearance
What is the underlying principle of adoption studies?
the comparison of criminals with their biological and adoptive parents
What were Mednick et al (1987) findings?
looked at court convictions - 14,000 adoptees among them
what was found after investigating criminal (bio and adoptive) parent records?
most adoptees had biological parents who were criminals
what issue does adoption studies overcome?
that biological and environmental factors have been separated
what does adoption studied show the importance of?
nature (genes) vs nurture (adopted family environment)
What environments are adopted children usually placed in?
similar to those of their birth parents
If most adoptees aren’t adopted immediately, what does that mean?
they spent time and ‘learnt’ from their bio parents environment
why are the ages 0 - 5 important?
that is the time when most children learn to imitate their parents actions
What does Jacob et al (1965) theory suggest?
that criminality can be attributed to a chromosomal abnormality
What is XYY syndrome?
a genetic condition - males have an extra ‘Y’ chromosome
(occurs in 1 in 1,000 males)
What did Jacob suggest?
that men with XYY were more aggressive
- as they were overrepresented in prison (15 to 1,000)
