comparable genes in the insulin/IGF-1 path-
genes in humans?
way of humans. Scientists then determine
whether the genes are linked to longevity in
The human genetic blueprint, or genome,
humans by looking to see if a variant of the
consists of approximately 25,000 genes made
genes is prevalent among people who live
up of approximately 3 billion letters (base
healthy, long lives but not for people who have
pairs) of DNA. Small deviations in the base
an average health span and lifespan.
pairs naturally occur about once in every
In one NIA-funded project, researchers
1,000 letters of DNA code, generating small
studied 30 genes associated with the insulin/
genetic variants. Scientists are finding that
IGF-1 pathway in humans to see if any vari-
some of these variants (polymorphisms) are
ants of those genes were more common in
actually associated with particular traits or
women over 92 years old compared to women
chance of developing a specific disease. People who were less than 80 years old. Variants with a certain trait, for example, those living
of certain genes—like the FOXO3a gene—
past age 100, may be more likely to have one
predominated among long-lived individuals,
variant of a gene, while people without the
suggesting a possible role with longer lifespan.
same trait may be more likely to have another This finding provides evidence that, like in variant. While it is very difficult to prove that
animal models, the insulin/IGF-1 pathway has
14
GENETICS
HUMAN GENETIC BLUEPRINT
CELL
23 PAIRS OF CHROMOSOMES
GENES