twins and Brendgen et al. Flashcards
describe identical twins
-monozygotic (MZ) twins.
-they come from one fertilised egg.
-they have identical genes as there is one sperm, egg and product of fertilisation.
-the DNA is 100% the same and always same sex.
describe the characteristics within identical twins
-if a characteristic is genetic, then MZ twins should both show that characteristic.
-no characteristic connected with behaviour is shared completely by MZ twins- there is always some influence from the environment.
describe non-identical twins
-dizygotic (DZ) twins.
-they come from two fertilised eggs.
-since they develop from different eggs, DNA of DZ twins is only as similar as siblings, it is not 100% the same.
describe the characteristics of non-identical twins
-if a characteristic is genetic, DZ twins would be expected to share that characteristic to an extent.
-when both twins share a characteristic it is known as a concordance rate (to what extend do both twins carry a characteristic)
what were the examiners researching in brendgen et al (2005)?
the genetic and environmental effects on socials and physical aggression using 6 year old twins.
what were the 3 aims of brendgen et al?
-to see if social aggression could be caused by genes or the environment.
-to see if one type of aggression leads to another type.
-to see if social aggression shared the same cause as physical aggression.
what was the starting sample?
322 pairs of twins age 6 born between nov 1995-july 1998 from quebec newborn twin study.
how many pairs of twins had complete data at all stages of the study?
why?
-234 (MZ twins male=44 female=50) (DZ twins male=41 female=32 mixed=67)
-parents may have taken them out
how was the data gathered?
longitudinally at 5,18,30,48 and 60 months then again at 6 years.
data consisted of two ratings:
-teacher (on a 3-point scale)
-classmates
what are two strengths for correlations in twins?
-high in validity
-both MZ and DZ twins share thier environment so there is a natural control over environmental effects.
-this means we can be sure any differences in concordance rates are unlikely to be due to environmental effects
-it is useful as MZ twins share 100% of their DNA showing there is no other way to study genetic influences so clearly
when was the ratings gathered?
in the spring term of the school year to ensure twins were well known by those providing the ratings of their behaviour.
how were the teachers ratings and measures?
Teachers questionnaires asked them to rate each child on a 3-point scale on the 6 statements 1-sometimes 2-often 0-never
-tries to make others dislike a child
-says bad things/spreads nasty rumours about another child.
-becomes friends with another child for revenge
-gets into fights
-physically attacks others.
-hits, bites or kicks others.
what were the childrens tasks
They were shown photos of their classmates and asked to circle photos of 3 children who best fit these 4 descriptions:
-tells others not to play with a child (social aggression)
-gets into fights (physical aggression)
-tells mean secrets about another child
-hits, bites or kicks others.
what type of score was each twin given?
a physical and social aggression score from teachers ratings.
any peer selections on social or physical descriptions that were made of each twin were also recorded.
what were the results for aim 1?
in both teacher and peer ratings for twins there were higher correlation between ratings of MZ twins of physical aggression than between same sex DZ twins.
strong positive correlation for MZ twins on physical aggression scores for social aggression were roughly equally correlated in MZ and DZ twin pairs.
