Ask A Scientist© Molecular Biology Archive

name        sandy
status      educator
age         50s

Question -  How does one explain the difference between multiple
alleles and polygenic inheritance?

For the sake of simplicity, we usually teach genetics using
examples with only two possible alleles (A and a).  But a single gene
can actually have many possible alleles (A, a, A1, A2, A', etc.).  For
example, hair color in mice is determined by a single gene with a
series of alleles, each resulting in different coloration.  There are
alleles for black, brown, agouti, gray, albino, and others.  The twist
here is that the same allele can be dominant or recessive depending on
context.  Allelic series are often written as
agouti > black > albino.
This means that agouti is dominant to black, and black is dominant to
albino.  (And agouti is necessarily also dominant to albino.)
If the black allele is in the presence of an agouti allele, the
mouse will be agouti because black is recessive to agouti.  If that same
black allele is paired with an albino allele, the mouse will be black
since black is dominant to albino.

Polygenic traits are the result of the interaction of several genes. For
instance, phenotypes like high blood pressure (hypertension) are not the
result of a single "blood pressure" gene with many alleles (a 120/80
allele, a 100/70 allele, a 170/95 allele, etc.)  The phenotype is an
interaction between a person's weight (one or more obesity genes),
cholesterol level (one or more genes controlling metabolism), kidney
function (salt transporter genes), smoking (a tendency to addiction), and
probably lots of others too.  Each of the contributing genes can also have
multiple alleles.

Christine Ticknor
Ph.D. candidate
Yale University
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Multiple alleles are different forms of the same gene...that is the sequence
of the bases is slightly different in the genes lovcated on the same place
of the chromosome.  In polygenesis there is more than one gene involved and
their may be multiple alleles of the multiple genes...which is far more
complex...involving potentially a number chromosomes.

PF
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Alleles are different versions or forms of ONE gene.  For example, there can
are 3 alleles (A, B, and O) that contribute to blood types in humans.  Each
person can have only two versions of the trait in their genome at one time,
but in the population there are 3 forms.  In fruit flies, there are many
different versions of eye color in the population, but one fly can have only
2 alleles at a time.  Polygenic traits are those where more than one GENE
contributes to the phenotype.  For example, the current model of skin color
is that there are 3 genes that contribute to skin color.  So there are 6
total alleles, 3 from the mother and 3 from the father.
Multiple alleles=more than two forms of the same gene in the population
Polygenic traits=more than one gene contributes to the phenotype


vanhoeck
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