Silencing of duplicate genes: a null allele polymorphism for lactate dehydrogenase in brown trout (Salmo trutta) |
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Authors: | F W Allendorf G St?hl N Ryman |
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Institution: | Department of Zoology, University of Montana, Missoula 59812. |
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Abstract: | A previously described isozyme polymorphism at one of two skeletal muscle
LdhA loci in brown trout is due to a null allele, Ldh1(n), producing no
detectable catalytic activity. Homozygotes for this allele have
approximately only 56% of the LDH activity in skeletal muscle relative to
homozygotes for the active allele. The remaining activity results from
enzyme subunits produced by other LDH loci. The Ldh1(n) allele is common
and widespread throughout brown trout populations in Sweden and is also
found in populations from Ireland. The persistence of duplicate gene
expression for the LdhA loci in almost all salmonid species is best
explained by natural selection against individuals containing null alleles.
However, there is no indication of natural selection against brown trout
with the Ldh1(n) allele: We suggest that the selection against individuals
containing null alleles that is apparently responsible for the persistence
of duplicate LdhA loci in salmonids occurs only under certain environmental
conditions.
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