Heterozygosity excess at the cattle<i>DRB</i>locus revealed by large scale genotyping of two closely linked microsatellites

Haeringen, Wa. Van; Gwakisa, Paul; Mikko, Sofia; Eythórsdóttir, Emma; Holm, Lars‐Erik; Olsaker, I.; Outteridge, P.M.; Andersson, Leif

doi:10.1046/j.1365-2052.1999.00436.x

Cited by 13 publications

(8 citation statements)

References 14 publications

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“…Nevertheless, we detected a trend of lower values of observed homozygosity in comparison with the expected one (33 in 36 breed/loci combination). This trend was also found by van Haeringen et al. (1999) when analysing the DRBP1 and DRB3 microsatellites in 23 cattle breeds from Northern Europe and Africa.…”

Section: Allelic Richness (Ar) Observed (Ho) Expected (He) Heterozsupporting

confidence: 58%

Genetic variation in BoLA microsatellite loci in Portuguese cattle breeds

Bastos-Silveira

Luı́s

Ginja³

et al. 2009

Animal Genetics

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Major histocompatibility complex (MHC) typing based on microsatellites can be a valuable approach to understanding the selective processes occurring at linked or physically close MHC genes and can provide important information on variability and relationships of populations. Using microsatellites within or in close proximity with bovine lymphocyte antigen (BoLA) genes, we investigated the polymorphisms in the bovine MHC, known as the BoLA, in eight Portuguese cattle breeds. Additional data from non-BoLA microsatellite loci were also used to compare the variability between these regions. Diversity was higher in BoLA than in non-BoLA microsatellites, as could be observed by the number of alleles, allelic richness and observed heterozygosity. Brava de Lide, a breed selected for aggressiveness and nobility, presented the lowest values of observed heterozygosity and allelic richness in both markers. Results from neutrality tests showed few statistically significant differences between the observed Hardy-Weinberg homozygosity (F) and the expected homozygosity (F(E)), indicating the apparent neutrality of the BoLA microsatellites within the analysed breeds. Nevertheless, we detected a trend of lower values of observed homozygosity compared with the expected one. We also detected some differences in the levels of allelic variability among the four BoLA microsatellites. Our data showed a higher number of alleles at the BoLA-DRB3 locus than at the BoLA-DRBP1 locus. These differences could be related to their physical position in the chromosome and may reflect functional requirements for diversity.

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Section: Allelic Richness (Ar) Observed (Ho) Expected (He) Heterozsupporting

confidence: 58%

Genetic variation in BoLA microsatellite loci in Portuguese cattle breeds

Bastos-Silveira

Luı́s

Ginja³

et al. 2009

Animal Genetics

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“…For the MHC class II, we found that three populations, the Big Qualicum, Puntledge, and Kitsumkalum, exhibited heterozygosity that significantly exceeded Hardy-Weinberg expectations. Other studies of the MHC have also found higher levels of observed heterozygosity than expected, suggesting that selection for heterozygotes is occurring in many species (for example, Seddon and Baverstock, 1999;van Haeringen et al, 1999;Peters and Turner, 2008;Oliver et al, 2009;see Garrigan and Hedrick, 2003 for review). In a recent study, we have shown that MHC class II heterozygous Chinook salmon fry exhibit fewer bacterial infections that do homozygotes (Evans and Neff, 2009).…”

Section: Evans Et Almentioning

confidence: 99%

MHC genetic structure and divergence across populations of Chinook salmon (Oncorhynchus tshawytscha)

2009

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The major histocompatibility complex (MHC) is thought to be under strong selection pressure because of its integral role in pathogen recognition. Consequently, patterns of MHC genetic variation should reflect selection pressures across the landscape. We examined genetic variation and population genetic structure at the MHC class I-A1 and class II-B1 exons in five Chinook salmon (Oncorhynchus tshawytscha) populations from two geographic regions in British Columbia, Canada. We then compared estimates of population structure at the MHC genes with neutral estimates based on microsatellites to examine the potential for local adaptation at the MHC. Chinook salmon are in decline throughout much of their native range and understanding the degree of local adaptation exhibited by the MHC may be important in conservation planning. Comparisons among populations yielded higher G 0 ST estimates for the MHC class I than expected under neutrality based on the microsatellites. In contrast, the MHC class II tended to exhibit lower G 0 ST values than did the microsatellites. These results suggest that across populations unique selection pressures are driving allele frequency differences at the MHC class I but that the MHC class II may be the subject of homogenizing selection. Rates of nonsynonymous versus synonymous substitutions found in codons associated within the MHC class I and II peptide-binding regions provided strong evidence of positive selection. Together, these results support the hypothesis that selection is influencing genetic variation at the MHC, but suggest that selection pressures may vary at the two classes of loci both at the sequence and population levels.

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“…MHC-embedded microsatellite loci in European sheep breeds were found to be highly polymorphic as is the case in a number of other domestic ungulates (Paterson, 1998;van Haeringen et al, 1999). Both the number of alleles per locus and the genotypic diversity as measured by the expected number of heterozygotes are consistently higher compared to other microsatellite loci dispersed throughout the sheep genome.…”

Section: Discussionmentioning

confidence: 69%

“…The analysis of variation at these loci has produced contrasting results. High polymorphism and heterozygote excess relative to neutral expectations were observed in cattle (van Haeringen et al, 1999) and in free living Soay sheep (Paterson, 1998), while no deviation from Hardy-Weinberg equilibrium was found in a sample of Dutch people (Moghaddam et al, 1998). Low levels of variation and no evidence of selection were reported in bighorn sheep (Boyce et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

Selection on MHC-linked microsatellite loci in sheep populations

et al. 2007

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Microsatellites within the major histocompatibility complex (MHC) region have received increasing attention as proxy measures of the level of polymorphism at the Mhc genes themselves. We assessed the diversity of microsatellite loci within or in close proximity of the Mhc genes in several breeds of domestic sheep (Ovis aries) and the wild Mouflon (Ovis orientalis musimon). This was compared to variation at other microsatellite loci scattered throughout the sheep genome. Significantly higher number of alleles were observed at the MHC microsatellites. The sheep breeds studied fell into high-and low-diversity group. This grouping is not related to the agricultural use of the breeds, whether for milk, meat or wool. It is, however, correlated with the geographic origins of the breeds. Southern breeds are genetically more diverse than northern breeds. The observed heterozygosity was in most cases lower than Hardy-Weinberg expectations. The potential impact of selective breeding by man on this is discussed. Neutrality tests indicated that for most of the breeds, the distribution of alleles at the MHC-linked microsatellites are more even than would be expected if the genes were neutral and sampled from populations under driftmutation equilibrium. Hitchhiking due to tight linkage with alleles at the MHC loci that are under balancing selection is proposed as a possible explanation for this pattern.

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Heterozygosity excess at the cattleDRBlocus revealed by large scale genotyping of two closely linked microsatellites

Cited by 13 publications

References 14 publications

Genetic variation in BoLA microsatellite loci in Portuguese cattle breeds

Genetic variation in BoLA microsatellite loci in Portuguese cattle breeds

MHC genetic structure and divergence across populations of Chinook salmon (Oncorhynchus tshawytscha)

Selection on MHC-linked microsatellite loci in sheep populations

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