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2005-07-05 16:55:44 | Hit : 26520 | Vote : 9077 |
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[ÀÚ·á] Major histocompatibility complex (MHC) variation in the endangered Mexican wolf and related canids |
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Major histocompatibility complex (MHC) variation in the endangered Mexican wolf and related canids
PHILIP W. HEDRICK*, RHONDA N. LEE & KAREN M. PARKER¢æ
Department of Biology, Arizona State University, Tempe, AZ 95287, U.S.A.
We have examined in Mexican wolves and related canids the amount of genetic variation for a class II gene in the major histocompatibility complex (MHC), thought to be part of the most important
genetic basis for pathogen resistance in vertebrates. In Mexican wolves, descended from only seven founders over three lineages, there were five different alleles. These were in three phylogenetic groups, only one of which was shared between lineages. Using single stand conformation polymorphism (SSCP), we found that in samples of animals from the two polymorphic lineages, the observed
heterozygosity was 0.74 and the genotypes were not different statistically from Hardy¡¾Weinberg proportions. The Ghost Ranch lineage of Mexican wolves was monomorphic for the locus, consistent
with the lower level of variation found previously for microsatellite loci and predicted from pedigree analysis. Samples of grey wolves, red wolves, and coyotes had 16 additional alleles. One Mexican wolf
allele was also found in grey wolves and another allele was shared between grey and red wolves. Most of the nucleotide variation resulted in amino acid variation and there were five different amino acids found at two di•erent positions. Only two of the 21 variable amino acid positions had solely synonymous nucleotide variation. The average heterozygosity for eight individual amino acid positions in the Mexican wolves was greater than 0.4. The estimated rate of nonsynonymous substitution was 2.5 times higher than that for synonymous substitution for the putative antigen binding site positions, indicative of positive selection acting on these positions. Examination of the known dog sequences for this locus showed that one of the Mexican wolf alleles was found in dogs and that the allele found in both grey and red wolves is also found in dogs.
Keywords: adaptive variation, dogs, heterozygosity, phylogenetic tree, substitution rate.
Heredity 85 (2000) 617¡¾624 Received 1 March 2000, accepted 27 September 2000 |
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