Hereditary Influences on Development
Genotype - the entire genetic makeup of a given person
Phenotype - all the genetic traits that are expressed in a person
A variety of phenotypes are possible
for each genotype.
Alcoholism
There is evidence that alcoholism has a genetic component:
- some ethnic groups have a higher proportion of alcoholics
- some people react to alcohol in ways that discourage drinking
Alcoholism is not simply a biochemical reaction:
- if the culture promotes drinking, alcoholism is more likely
- if the culture discourages or prohibits drinking, alcoholism is less likely
- alcoholism is most likely to develop between the ages of 15 and 25
alcoholism is not inevitable, whatever the genotype
Schizophrenia
Mortensen (1999) - study involved 2 million
Danes born between 1935 and 1978
10% of people who had a close relative with schizophrenia themselves had the disorder
Other risk factors:
1. birth month
2. place of birth
What does the genotype set?
Canalization - when the developmental outcomes for a phenotype are restricted to a small
number of outcomes, e.g., babbling in infancy
Reaction Range - the upper and lower limits of an attribute in the phenotype, set by the
genotype
Examples:
- physical changes at adolescence
- graying at ...
- IQ
Heritability - the trait variability in a population that is determined by variations in genetic inheritance
Heritability measurements take into account both genetic and environmental factors.
- if a genetically similar population shows marked individual differences, they must be the
result of environmental factors
- if a population within a similar environment shows marked individual differences, they must
be the result of genetic factors
Genotype/Environment Interaction
Scarr (1992) - the genetic uniqueness of individuals results in the creation of unique
environmental experiences
Passive genotype/environment correlation
- musical parents may both pass on their musical genes and provide a home environment
that is rich in musical experiences
Evocative genotype/environment correlation
- genetically influenced attributes may affect others' responses: a cranky baby or a nonresponsive baby may discourage playful interaction
Active genotype/environment correlation
- children choose environments that are compatible with their predispositions: sociable
children are likely to search out companionship
Genetic differences become more influential across development as individuals mature and do
their own "niche-picking."
Shared environmental influences - experiences that individuals living in the same home share, e.g.,
parental interests, church attendance,
Non-shared environmental influences - experiences that individuals living in the same home do not
share, e.g., sibling relationships, family income (over time)
- the impact of genotype may lead to microenvironments, environmental characteristics that are
specific to a child