Biology Reference
In-Depth Information
BOX 16.1
(cont'd
)
Gene Flow: A Hypothetical-but-
Easy-to-Imagine-in-Real-Life Case
Study
Imagine that a group of blue-eyed Danes
moves to a small village in Zaire, in which
all Zairians without exception have brown
eyes. This sudden influx of gene variants
that lead to blue eyes being present in the
Zairian village is gene flow. The blue eye
version (or allele) of an eye color gene
has flowed into the population. Before the
movement of blue-eyed people into the
village, the Zairian village population had
100% brown alleles, whereas afterwards, it
becomes more like 30% blue to 70% brown
alleles. The gene frequency of the blue allele
has increased in this village population due
to gene flow.
4
Itan, Y., Jones, B.L., Ingram, C.J., Swallow, D.M.,
Thomas, M.G., 2010. A worldwide correlation of
lactase persistence phenotype and genotypes. BMC
Evolutionary Biology 10, 36, online publication.
5
Gerbault, P., Liebert, A., Itan, Y., Powell, A., Burger,
J., Swallow, D.M., Thomas, M.G., 2011. Evolution of
lactase persistence: an example of human niche
construction. Philosophical Transactions of the Royal
Society London, B, Biological Sciences 366, 863-877.
6
Cochran, G., Harpending, H., 2009. The 10,000 Year
Explosion: How Civilization Accelerated Human
Evolution. Basic Books, New York.
7
Kemp, B.K., Schurr, T.G., 2010. Ancient and modern
genetic variation in the Americas. In Auerbach, B.M.
(Ed.), Human Variation in the Americas: The Inte-
gration of Archaeology and Biological Anthropology.
Center for Archaeological Investigations, Carbondale,
IL, pp. 12
e
50.
Population Genetics
The field of population genetics concerns itself with understanding how these evolu-
tionary forces combine with population demography to ultimately produce evolutionary
change short and long term. Since about the 1920s, population geneticists have been
developing analytical (mathematical) and simulation models that are used to evaluate
actual, observed genetic data vis-
`
-vis hypothetical evolutionary scenarios. Many of
the interpretive tools presented below are based on innovations in population genetic
theory.
Population genetic theory is important to understanding
population structure
and its
history. Population structure is the study of the relationship between group composition
(including size), mating practices, and genetic drift. Studies of population structure ask
what mechanisms impact the observed pattern in the genetic variation of populations.
Studies of
population history
ask whether any similarities or differences in population struc-
ture between two or more populations are due to a shared ancestry or mate exchange
(
Harpending and Jenkins, 1973
).
This concept of “
population history
” is often contrasted with that of “
adaptive
history
.” When embarking on an investigation of population history, you are essentially
attempting to understand what factors have shaped genetic variation in your sample,
except
for natural selection. In contrast, an investigation of adaptive history is a study
of the history of natural selection on one or more traits exhibited by the population sample
in question.
