Quantitative Trait Loci
Loci that contribute to the variance of a continuously distributed characteristic.
The proportion of a sample of pairs of relatives (e.g. twins) who both show a particular
trait or disease. The most useful way of calculating concordance is ‘‘probandwise,’’ that
is, a series of twins is ascertained via affected index cases or probands. The
probandwise concordance is then simply the number of affected cotwins divided by the
total number of cotwins.
Strictly, relative risk is the proportion of individuals exposed to a risk factor for a
disorder who are affected divided by the proportion of nonexposed individuals who are
affected. In genetic studies, the term is sometimes used slightly more loosely to refer to
the proportion of relatives of affected individuals of a particular type (e.g. siblings) who
are affected, divided by the proportion of the general population who are affected.
The causes of a particular disorder.
Variable Number Tandem Repeat (VNTR)
A small motif of DNA that is repeated tandemly a varying number of times to produce
alleles of different sizes.
Single Nucleotide Polymorphism (SNP)
A nucleotide substitution occurring within DNA.
An individual identiFed as having a characteristic or disorder of interest through whom
other family members are ascertained.
An observable characteristic of an individual.
Behavior genetics is the study of the inheritance of normal psychological traits, such
as personality and cognitive ability, as well as abnormal traits and illnesses, such
as mood disorders and psychoses. The questions addressed by behavior genetics
include the following: Why do individuals differ? Why aren’t children of the same
parents alike? To what extent are genes and environmental factors accountable for
the differences and similarities in human behavioral traits? What are the salient