Heritability
the proportion of this total variation between individuals in a given population due to genetic variation
The question of whether a trait is heritable is a about
the role that differences in genes play in the phenotypic differences between
individuals or groups within a population
Heritability estimates for IQ are around
0.5, Some estimates as high as 0.8
what are the three major considerations of heredibility
- A heritability coefficient is always specific to a
particular population at a particular time - Heritability is a measure of variation
- A high heritability coefficient does not mean that a trait “is genetic”
- A heritability coefficient is always specific to a
particular population at a particular time
the heritability of weight is approximately 0.6 in North America. Would this coefficient be expected to change if we measured it 1000 years ago in Medieval
England?
- Heritability is a measure of variation
For some attributes there may be no person-to-person variation
- A high heritability coefficient does not mean that a trait “is genetic”
If the heritability of weight was 1 would this mean that one’s weight is 100% determined by genes? No, Genes cannot be understood outside the context of the
environment with which they interact.
2nd consideration of heretibility example
tried to determine the heritability of
“having a heart” found that h2 was equal to 0. What
does that mean?
heart development is strongly influenced by genes and there is no variation across the sample :
everyone has a heart so the coefficient is 0
3rd consideration of hereditability explanation
heritability coefficient of 1 does mean that trait differences
between individuals within a population at a time are due to genetic factors. if a certain portion of the trait is invariant across the population, heritability does not account for genetic influences on the portion of the trait that does not vary. – Also, if you change the population/time, you will change the
heritability coefficient
3 laws of the genetics of complex traits
- Intelligence has some genetic basis
- Intelligence is not
100% heritable - Intelligence may be caused by many genes of small effect
- Intelligence has some genetic basis
- Rett syndrome
- William Syndrome
- Fragile X syndrome
rett syndrome
rare genetic neurological disorder that mainly affects girls.
leads to severe cognitive and physical impairments. often experience loss of purposeful hand skills, impaired motor functions, repetitive movements (such as hand-wringing), and problems with communication and social interactions
willimas syndrome
genetic condition characterized by developmental delays, learning disabilities, and distinct facial features. They may face challenges in spatial tasks and have a higher likelihood of heart problems
fragile x syndrome
a genetic disorder more common in males that causes intellectual disability, behavioural challenges, and various physical characteristics. often have social and communication difficulties and repetitive behaviours, and may exhibit symptoms of autism spectrum disorder, hyperactivity and sensory sensitivities
- Intelligence is not 100% heritable
- All traits show some
environmental influence - also Interplay
between genes and
environment
IQ = Genes + Environment
+ Interaction + error
Gene x Environment interaction
An interaction effect is not the same as a correlation
Interaction effects quantify how genetic characteristics can change the influence of an environmental variable
gene x environment interaction example
researchers were able to identify a gene that was associated with severe violent behaviour, but only for individuals who had been victims of abuse during childhood.
Individuals who had not been victimized, but who carried the
gene were less likely to commit violence
- Intelligence appears to be caused by many genes of small effect
(polygenic model)
Genome-wide association (GWA) studies
- Benyamin et al 2014
- 18 000 children
- No genome-wide significant associations of IQ with 1 gene
- Largest effect sizes = 0.2% of the variance of intelligence scores
Desrivieres et al 2014
- 1500 children
- Largest effect sizes = 0.5% of the variance of intelligence scores
- Genes can also interact (i.e., the expression of one gene might depend
on the presence of another gene)
human genome project allows
estimates of genetic influence on
complex traits using genome-wide genotypes
in large samples of unrelated individuals
what is the human genome project limited to
additive genetic variance
Heritability of intelligence increases from
infancy to adulthood.
Small genetic differences are magnified as children select, modify and create environments
correlated with their genetic propensities (active model of selected environments)
simplified of first of the five main findings
Proximal vs distal effect of genes
