Role of genetic factors in intelligence test performance

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Psychology unit 3 intelligence
Role of genetic factors in intelligence test performance
Bouchard and McGue investigated MZ twins who were reared apart in separate
environments and found a closer similarity in IQ scores even though they were
separated as they had concordance rates of 72% compared to DZ twins who were
reared together and had concordance rates of 60%. Therefore genes play a clear
role in IQ performance as their influence was greater than twins who had been
brought up in the same environment, suggesting genes are more influential than the
Removes confounding variable of nurture so we can be sure the findings are due
to genes
Malouf reviewed 9 meta analyses and found that 48% of variance in intelligence
was due to genes and 41% of variance in processing speed was due to genes. This
shows that genes do play a role in IQ performance as some results were due to
genes, however as rates weren't 100% genes aren't the only reason for intelligence
so other factors such as environmental factors may also play a role too.
Good population validity
Didn't separate nature from nurture so we don't know the extent to which the
rates were due to genes
Texas adoption project involved 300 American families where children of
unmarried mothers were adopted into another American family. Found that
children had stronger correlations with the environment and IQ than correlations
between genes (biological mothers) and IQ when they were younger. But when they
were older genetic factors (biological mothers) had the strongest correlation with
IQ as children became less influenced by their environment as they became more
independent and were more able to make decisions, therefore the role of genes is
greater in older children but less influential in younger children.
Separates nature from nurture so we know genetic factors weren't due to the
Correlational- doesn't show that genes cause intelligence
IGF2R gene: Plomin found that 32% of children who were classed as `super bright'
had this gene compared to 16% of those who were classed as average. This suggests
that genes are important as children with higher IQ's had this gene suggesting it
plays a role in determining their intelligence
Not the only gene that influences intelligence as not all of the super bright
group have that gene so the role of genes involves the use of more than one gene.

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Psychology unit 3 intelligence
FADS2 gene found to promote intelligence if the child was breastfed as this
interacted with the C version of the gene. Children who had the weaker G version
of the gene didn't show this increase. This shows that the role of genes is
important but it's influenced by environmental factors as both nature and nurture
combined to measure intelligence
Turkenhiemer found genes play a larger role in intelligence if children are from a
poorer background.…read more


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