heritability issues Flashcards
(28 cards)
what is genotype?
genotype is the genetic constitution of an individual
can learn about genotype by observing DNA
what is phenotype?
the phenotype is an observed quality of an organism e.g. eye colour, personality traits etc
phenotype is influenced by genotype + environment
what is heritability?
heritability is a statistical measure that expresses a proportion of the observed variability in a trait that is a direct result of genetic variability
three types of genetic variance
additive
dominant
static
what is additive genetic variance?
genetic variation in behaviour, personality or intelligence as a function of the individual’s genes inherited from parents
what is dominant genetic variance?
part of a process by which certain genes are expressed (dominant) and others are not (recessive)
what is epistatic genetic variance?
refers to epistasis which is a process by which genes interact
certain genes that we inherit determine whether other genes we inherit will be expressed or suppressed
what is broad sense heritability?
additive + dominant + static
what is narrow sense heritability?
additive genetic variance only
main heritability we look at
difference between heritability and immutability
heritability does not mean immutability
immutability is something that you can’t change whereas heritability can be changed e.g. by environment
methods of assessing heritability
family studies
twin studies
adoption studies
twin study using the Big Five
Riemann, Angleitna and Strelau (1997)
correlation for MZ twins was between 0.42 and 0.56
correlation for DZ twins was between 0.13 and 0.35
similar environments, different genes, different correlations
what is Falconer’s formula?
the heritability estimate = (the correlation for MZ twins - the correlation for DZ twins) x 2
x100 to get percentage
adoption study into extraversion
children are more similar to their biological than adoptive parents in respect to personality
genetic factors account for 20-50% of phenotypic variance
concordance rates of intelligence
Ridley (1999) showed concordance rates of IQ for strangers and relatives
Eysenck used data to conclude that the estimation of heritability of intelligence was about 69%
Recent estimates are more conservative and state that heritability of intelligence ranges from 40-80% with 50% commonly accepted in nowadays psychology
problems with assessing heritability
- Difficulty with measuring dominant and epistatic genetic variance
- No experimental control
- Twin and adoption studies involve families that are not necessarily representative of the normal population and so the genetic influences in these samples may not be representative of the whole population
e.g. twins are slightly less intelligent than non-twins on average likely due to rivalry over nutrients in the womb
e.g. in adoption studies, the adoptees are typically placed with stable and responsible adoptive families which reduces the variance in adoptive families and might inflate heritability estimates - Assortative mating can affect genetic variance and estimates of genetic heritability - people do not mate randomly but mate with those similar to themselves - the model is based on the assumption that heritability is random pairings so estimations may be skewed
- Some studies e.g. Brace (1996) show that heritability varies across cultures
environmental influences on intelligence
biological variables
family environment
school and education
culture
what are some biological variables that influence intelligence?
nutrition
lead
prenatal factors
how does nutrition influence intelligence?
nutrition and healthcare improvement are main factors responsible for the Flynn effect
malnutrition can impair brain function and IQ in the long-term
iodine deficiency during pregnancy can lead to retardation
longer breast-feeding is associated with higher verbal intelligence
vitamin-mineral supplements given to children found to increase non-verbal IQ scores
how does lead influence intelligence?
negative correlation between environmental exposure to lead and mercury and children’s intelligence
how do prenatal factors influence intelligence?
smoking and drinking during pregnancy is connected with health problems and brain damage to children
e.g. foetal alcohol syndrome - children are smaller than average, have characteristic facial abnormalities and are mentally retarded
what are some aspects of family environment that influence intelligence?
shared and non-shared environments
social and economic status
education
birth order
family size
how does shared and non-shared environment influence intelligence?
non-shared unique environmental factors have stronger influence on intelligence differences between individuals than shared environmental factors
what is shared environment?
refers to all common influences within a family that make children resemble each other e.g. parental attitudes to education, parental income etc
