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GENETICS: Research Note |
Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg 24061
2 Corresponding author: esmith{at}vt.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: heritage turkey • commercial turkey • microsatellite • genetic relatedness • genetic analysis
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Genetic variation within and among CO turkey populations was previously evaluated by Smith et al. (1996), Zhu et al. (1996), and Ye et al. (1998). Though Smith et al. (2005) also analyzed the genetic relatedness of 5 heritage turkey varieties, the relatedness between the CO and heritage turkeys has never been investigated. Information regarding the genetic relatedness between CO and heritage turkey varieties can be used for genetic improvement of the different turkey strains such as the introgression of novel genes important for economic traits including disease resistance.
Commercial turkeys have been highly selected for increased BW and growth rate. In turn, they have a relatively higher rate of susceptibility to diseases (Li et al., 2001; Huff et al., 2005) that may be due to a relatively narrow genetic background. There are only a few highly selected strains of the Large White variety, and these may lack the genetic diversity they need to be able to resist or tolerate diverse disease conditions. Indications are that emphasis in the turkey breeding programs on meat quantity and quality, but not on disease resistance, could have led to the increased vulnerability of the CO turkey to diseases (Christman and Hawes, 1999).
The relatively high vulnerability of CO birds to various disease conditions is of serious concern to the turkey industry. Because there is no comprehensive linkage map available for the turkey, exploring the turkey genome and thus identifying QTL for economic traits such as disease resistance in CO birds is impossible. The need to evaluate the status of turkey genetic diversity is attracting attention from poultry scientists, because it is now realized that the diversity of the non-CO turkey varieties are essential genetic resources that will enable breeders to improve their birds’ health and vigor or to respond to changing environmental conditions, production systems, or consumer needs (Christman and Hawes, 1999).
The objective of the current research was to conduct molecular genetic analysis of relatedness between CO and heritage turkey varieties including Bourbon Red (BR), Blue Slate (BS), Narragansett (NA), Royal Palm (RP), and Spanish Black (SB). Understanding this genetic relationship between CO and heritage turkeys may be useful in breeding programs that could involve the introgression of novel genes important for economic traits including disease resistance.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Twenty-five birds were used from each of CO, NA, BR, BS, SB, and RP varieties. Birds from the heritage varieties were obtained from Privett Hatcheries (Portales, NM) as day-old birds and raised at the Virginia Tech Turkey Farm using standard protocols. Though the genetic background of the heritage turkeys is unknown, the varieties are true breeding (Smith et al., 2005). Blood was collected by brachial venipuncture in tubes containing 0.5 M EDTA. Aliquots of 50 µL of blood were used for genomic DNA isolation according to Smith et al. (1996). Isolated genomic DNA from each sample was air-dried and dissolved in sterile water to a concentration of 50 ng/µL before use in PCR.
Microsatellite DNA Analysis
The sequences for the 10 primer pairs used in the present work are presented in Table 1
. These primers were previously described by Burt et al. (2003). The PCR amplifications were carried out in a final volume of 10 µL. Each reaction contained 50 ng of genomic DNA, 50 mM KCl, 10 mM Tris-HCl (pH 8.3), 1.5 mM Mg2+, 200 µM each deoxynucleotide triphosphate, 160 ng of each primer, and 1 U of AmpliTaq DNA Polymerase (Eppendorf, West-bury, NY). Amplifications were carried out in a Mastercy-cler Gradient Thermocycler (Eppendorf) under the following conditions: an initial denaturation step of 5 min at 95°C, followed by 38 cycles of denaturation for 45 s at 95°C; annealing for 45 s at optimized temperature (Table 1) and extension for 45 s at 72°C; with final extension for 7 min at 72°C. Electrophoresis of the amplified products was performed on a 4% metaphor agarose gel with 1% ethidium bromide at 40 V for 7 h). To test the efficiency of metaphor agarose in distinguishing among microsatellite alleles, PCR products of 2 SB samples amplified by the TUM20 primer and 1 amplified by the RHT0011 primer were randomly selected and genotyped using an ABI PRISM 3100 Genetic Analyzer (Applied Biosystems, Foster City, CA), and allele sizes were observed using Gene-Scan 3.7 (Applied Biosystems).
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The microsatellite alleles were analyzed by direct count within each population, and allele frequencies were computed according to Hartl and Clark (1997). Genetic distance was estimated according to Nei (1972), and these estimates were used to construct a consensus tree with bootstrap values using the neighbor-joining method in PHYLIP (Felsenstein, 1989) and visualized using TREE-VIEW (Page, 1996).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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for primer TUM20 with SB birds as template for the PCR. Two alleles were observed for ADL0023; 3 for the RHT0024, RHT0294, RHT0095, RHT0009, RHT0131, RHT0011, and TUM16 loci; and 4 for TUM20 and RHT0216. The genetic distance estimates among the 6 populations are presented in Table 1
. The lowest genetic distance was observed between the BS and the NA (0.07) and RP (0.07). The highest genetic distance was observed between the CO and the SB (0.40) and RP (0.41). The extended majority rule consensus tree with bootstrap values (Figure 2) depicts the genetic relationship among the 6 different populations, clustering the RP with the BS and the BR with the CO population. The clustering of the turkey populations was unstable, as indicated by the low bootstrap values, suggesting that these turkey varieties were very closely related and therefore no group clustering was observed at a significantly high frequency.
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The genetic relatedness among the heritage varieties appears to be consistent with that observed by Smith et al. (2005), but with a slight difference. When a tree was constructed using only the heritage varieties (data not presented), the SB clustered with the BR, which was the same observed by Smith et al. (2005). However, the tree showed a closer relatedness between RP and BS, unlike that observed by Smith et al. (2005), which showed closer relatedness between RP and NA. Considering that the NA was the second closest strain to RP, results of the current research and that of Smith et al. (2005) were actually showing that the BS, NA, and RP heritage varieties were genetically closely related.
The current studies provide a foundation on which CO turkeys could be improved using heritage turkeys. Though the bootstrap values were generally low, the use of randomly distributed microsatellite markers provides a level of support for the relationships estimated in the present work. Explanations that have been advanced for low bootstrap values, including a short internal branch (Hirt et al., 1999), could be responsible for the lack of statistical significance in the estimates observed here. However, the lack of statistical significance appears to support the long-held view that all turkey varieties are a single breed, because the use of 10 markers distributed on different chromosomes may represent the most unbiased estimate of the relationships to date. Using agarose in the genotyping will facilitate the use of these markers by a larger number of laboratories. For example, agarose gel-based genotyping of these microsatellite markers could be used to provide additional support for estimates of genetic relatedness among CO strains previously reported by Smith et al. (1996), Zhu et al. (1996), and Ye et al. (1998).
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Received for publication June 27, 2005. Accepted for publication August 10, 2006.
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REFERENCES |
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