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Human serum, the fluid
portion of the blood that remains after clotting, contains various
proteins that have been shown to be under genetic control. Study
of genetic influences has flourished since the development of
precise methods for separating and identifying serum proteins.
These move at different rates under the impetus of an electrical
field (electrophoresis),
as do proteins from many other sources (e.g., muscle or nerve).
Since the
composition of a protein is specified by the structure of its
corresponding gene, biochemical studies based on electrophoresis
permit direct 
study
of tissue substances that are only a metabolic step or two away
from the genes themselves. Electrophoretic studies have revealed
that at least one-third of the human serum proteins occur in variant
forms. Many of the serum proteins are polymorphic,
occurring as two or more variants with a frequency of not less
than 1 percent each in a population. Patterns of polymorphic serum
protein variants have been used to determine whether twins are
identical (as in assessing compatibility for organ transplants)
or whether two individuals are related (as in resolving paternity
suits). Whether or not the different forms have a selective advantage
is not generally known.
Gina
Kolata
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