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Problems and limitationsa
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Classical Genetic Studies
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Family studies
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Determine if family members of substance
abusers are at increased
risk for substance
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Generational and secular trends in drug
use.
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abuse.
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Nonpaternity.
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Provide evidence consistent with a genetic
basis
for the disorder (not conclusive).
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Inability to separate genetic from family
environmental effects.
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Segregation analyses
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Use the diagnostic status of family members
to
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Affected by statistical non-normality.
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determine the relative likelihood
of alternative
modes of transmission for
a familial disorder
(e.g., polygenic, single
major locus, mixed).
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No direct test of single locus versus
polygenic model of transmission.
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Twin studies
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Determine if within-pair similarity for substance
abuse is greater in genetically
identical twins
than in 50% genetically identical
fraternal twins.
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Requires accurate zygosity
determination.
Assumes equal relevant environments in
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identical and fraternal twins.
Rare subjects.
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Adoption studies
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Separate the effects of genes and environment
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Assumes no selective placement.
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by studying the similarity
between biological
parents, their adopted-away
children, and their
adoptive parents.
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Places prenatal environmental effects in
the genetic component.
Rarity of subjects.
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Molecular genetic studies
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Linkage analyses
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To use family data to statistically link
a trait to a
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Multiple statistical comparisons.
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genetic marker on a particular
chromosome.
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Assumes particular mode of
transmission.
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Rare multigenerational drug abuse
pedigrees.
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Generational and secular trends.
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Association studies
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To compare genetic variation at a specific
site in
affected and unaffected individuals.
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Appropriate control group.
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