ASSOCIAZIONE TRA MICROSATELLITI E CARATTERI MORFOLOGICI IN BOVINI DA CARNE

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DNA MICROSATELLITES ASSOCIATED WITH MORPHOLOGICAL TRAITS IN BEEF CATTLE

ROBERTACIAMPOLINI, ELISAMAZZANTI, DARIOCIANCI

SUMMARY

The objective of this research was to detect the relationship between DNA microsatellites and morpho-functional traits on Piemontese cattle breed in the attempt to find out major genes and the genomic markers associated with them. A set of 20 microsatellites was analyzed on 47 young double-muscled bulls in a performance test, for which somatic measurements were available. For every allele of each microsatellite, statistical analysis was carried out estimating the significance of the difference between somatic measurements average values of carrying and not carrying subjects. The study revealed numerous microsatellites with alleles significantly linked to positive or negative meat production traits. The most interesting results were represented by INRA 5, INRA 11, INRA 16, INRA 64 and ETH 131. Genomic formulae were examined: this led to originate two furthermost subpopulations that showed to be significantly distant from each other. The greater homogeneity (genetic similarities) was found in the group of sub- jects with alleles less implicated in meat traits compared to the subjects with positive alleles. The study revealed also that most microsatellites, both in positive and in negative subpopulations, did not respect Hardy-Weinberg proportions, with few microsatellites in clear disequilibrium. Moreover, coefficients for heterozygotes deficiency show the tendency towards homozygosis.

Key words: beef cattle, microsatellites, QTL.

RIASSUNTO

Scopo del presente lavoro è stato identificare le correlazioni tra microsatelliti e caratteri morfo-funzionali nella razza bovina da carne Piemontese, nel tentativo di evi- denziare geni ad effetto maggiore e marcatori genomici ad essi associati. È stato analiz- zato un panel di 20 microsatelliti su 47 giovani tori a groppa doppia in prova di performance per i quali erano disponibili misurazioni somatiche. Per ciascun allele di ciascun microsatellite è stata effettuata l’analisi statistica al fine di saggiare la significatività della differenza tra i valori medi delle misurazioni somatiche di soggetti portatori e non.

Lo studio ha rivelato la presenza di numerosi microsatelliti con alleli significativamente associati a caratteri positivi o negativi di produzione della carne. I risultati più interes-

Dipartimento di Produzioni animali - Direttore Prof. Paolo Verità.

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santi sono forniti dai microsatelliti INRA 5, INRA 11, INRA 16, INRA 64 ed ETH 131.

L’esame delle formule genomiche ha portato alla creazione di due sottopopolazioni estreme tra loro significativamente distanti. L’omogeneità (somiglianza genetica) mag- giore è stata riscontrata nel gruppo di soggetti portatori degli alleli meno implicati nei caratteri di produzione della carne se confrontati con soggetti portatori degli alleli positivi per tali caratteri. Lo studio ha rivelato, inoltre che la maggior parte dei microsatelliti, sia nella sottopopolazione dei soggetti positivi che in quella dei negativi, non rispet- tavano le proporzioni di Hardy-Weinberg e che alcuni microsatelliti manifestavano chia- ro disequilibrio. In aggiunta, i coefficienti di difetto degli eterozigoti hanno rivelato la tendenza verso l’omozigosi.

Parole chiave: carne bovina, microsatelliti, QTL.

INTRODUCTION

Meat production aptitude is dependent on the action of numerous genes; it can derive from the limited but combined effects of many genes as well as from the action of major genes, which may be obscured by gene interactions and modified by environmental factors.

Analyzing the action of single genes in polygenic traits is still out of the question because each locus, aside from contributing only par- tially to the genotype, undergoes variability deriving from other factors, both genetic (penetration, phenocopies, incomplete co-segrega- tion, parent-specific imprinting) and environmental, which make sep- aration of these effects problematic.

Several statistical strategies have been set up, based on the concept that on the whole some genes have a greater action than others in determining a trait; it would therefore be possible to separate their quantitative effect and identify associated markers which may justify up to 10 or 20% of the trait’s variability.

Anyway, the detection of major genes and of the genomic markers associated with them is a very promising research goal for reinforcing selective progress in quantitative traits by means of Marker Assisted Selection (MAS). Genetic linkage maps can provide the basis for determining Quantitative Trait Loci (QTL) and furthering genetic progress, especially for traits which may be difficult or expensive to measure such as carcass or meat quality (Stone et al., 1999).

Current research aims to establish a unified model of estimation for each QTL, in which various regions of the genome are assigned an importance proportional to the QTL variance which they explain. A

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unified model would permit better examination of additive effects, tracing alleles combinations, estimation and prediction of non-additive genetic effects such as heterosis and consanguinity (Haley &

Wischer, 1998). A methodology applied to the analysis of variability, which can also be applied to the study of QTL, was formulated by Ciampolini et al. (1995, 2000).

MATERIALS AND METHODS Somatic measurements

The study was conducted on 47 young double-muscled bulls in a performance test. The morpho-functional evaluations as established by the Breed Standard were performed by ANABORAPI (Associazione Nazionale Bovini di Razza Piemontese).

DNA analysis

DNA was purified from 20-ml samples of peripheral blood using the method described by Jeanpierre (1987). The PCR reactions and the procedures for determining the genotypes of the microsatellites were performed according to the methodology described by Vaiman et al. (1994). For this study 20 microsatellites were analyzed; 17 of these were produced in the INRA laboratories (Vaiman et al., 1994) and the rest by Steffen et al. (1993). Information concerning the 20 microsatellites is shown in Table I.

Statistical analysis

The average values of the somatic measurements of subjects carrying every allele of each microsatellite were calculated; these were compared statistically with the average values of subjects not carrying the allele, and the significance of the difference was estimated using the J.M.P. computer programme (1996). The subjects carrying alleles with positive or negative implications for meat traits were grouped in subpopulations and the biosys computer package (Swofford & Selander, 1989) was applied for the calculation of allele frequencies, Hardy- Weinberg proportions, excess or deficiency of heterozygotes and genetic distance according to Cavalli Sforza and Edwards (1967).

The genetic similarities between and within populations were esti-

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Tab. I.Analysed microsatellites and their polymorphism. Numbers MarkerLocusChromosomeBibliographyof alleles INRA5D12S412Vaiman et al., 19945 INRA6D3S93Vaiman et al., 19946 INRA11D1S61Vaiman et al., 199410 INRA13D16S1016Vaiman et al., 19949 INRA16D27S2027Vaiman et al., 199410 INRA23D3S103Vaiman et al., 199411 INRA25D17S617Vaiman et al., 19948 INRA27D27S1627Vaiman et al., 19946 INRA31D21S1221Vaiman et al., 19946 INRA32D11S911Vaiman et al., 19949 INRA35D16S1116Vaiman et al., 19947 INRA37D4S264Vaiman et al., 199412 INRA50D15S515Vaiman et al., 199410 INRA53D7S67Vaiman et al., 19945 INRA63D18S518Vaiman et al., 19947 INRA64D23S1523Vaiman et al., 19946 INRA72D4S114Vaiman et al., 199410 ETH 131D21S421Steffen et al., 199313 ETH 152D5S15Steffen et al., 19937 ETH 225D9S19Steffen et al., 19935

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mated according to the method of Ciampolini et al., (1995) based on the Individual Multilocus Genotype (IMG). Each subject was defined according to its own multilocus genotype (in our case, 20 microsatellite loci) consisting of a series of 40 alleles. In order to estimate the genetic similarity between two individuals, or groups of individuals, the proportion (P) of shared alleles (A) in relation to the 2L possibili- ties (L = number of loci considered) was calculated.

Genetic similarity was measured by P = A/2L. The similarities calculated for each pair of subjects were averaged in order to obtain similarity values between breeds or subpopulations. To estimate the similarity (or the genetic distance) between breeds or subpopulations the average values of the similarities between each subject of a group and each subject of the comparison group were calculated.

RESULTS

The study revealed numerous microsatellites with alleles significantly linked to positive or negative meat production traits. The most interesting of the 20 cases we studied were microsatellites INRA 5 (locus D12S4), INRA 11 (locus D1S6), INRA 16 (locus D27S16), INRA 64 (locus D23S15), ETH 131 (locus D21S4), with alleles present in subjects with greater somatic development, and obviously dif- ferent alleles present in less-developed subjects.

In order to point out the differences on a somatic level, we calculated the average values of somatic measurements in subjects carrying the most significant and interesting alleles (both positive and negative). These values, compared to the average values of the measurements of the non-carrier individuals, at times show significantly dif- ferent values (P < 0.01 or P < 0.05).

In particular, the INRA 5 microsatellite (chromosome 12) presents Allele 4 in those subjects with most of the measurements, as well as a live weight at 250 and 300 days, greater than that of non-carrier subjects (P < 0.01). On the other hand Allele 3 was present in many less- developed subjects (but for P < 0.05). As shown in Table II, the differences between the subjects carrying Allele 4 and those with Allele 3 were particularly noticeable, arriving at a 2-cm difference in hight and a 20-kg weight difference.

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Tab. II.Somatic measuraments of animals evidencing alleles at locus D12S4 (INRA5) associatedawith beef characters. Subjets withOtherSubjets withOther allele 4subjetsallele 3subjets MeanSDbMeanSDMeanSDMeanSD Height at withers, cm118.81*1.91117.311.87116.77*1.78118.531.96 Height at pelvis, cm126.60**1.72125.011.58124.76*1.42126.251.81 Depth of chest, cm61.39**1.0460.440.9560.28*0.8661.181.09 Body lenght, cm142.49**2.90139.812.66139.39*2.39141.893.05 Chest lenght, cm77.21**0.9876.300.9076.15*0.8177.011.04 Lenght of rump, cm50.49**0.7949.760.7349.64*0.6650.320.83 Width of brisket, cm40.430.8839.960.7939.800.7140.340.87 Width of chest, cm43.820.8543.630.6443.450.5243.810.81 Fore width of rump, cm43.50**0.9642.610.8842.47*0.8043.301.01 Medium width of rump, cm45.71*1.0145.070.9644.970.9445.571.03 Hind width of rump, cm38.960.8938.470.8338.390.8238.850.90 Lenght of head, cm43.801.4943.120.9943.570.9743.551.43 Crest girth, cm182.682.95181.402.69181.202.73182.392.92 Fore cannon girth, cm18.95*0.3318.680.3118.630.2818.890.35 Buttock girth, cm140.696.42140.084.03139.503.32140.615.97 Weight at 150 d, kg161.715.90160.075.72157.946.93161.685.53 Weight at 250 d, kg322.51**22.04303.4618.87302.5117.23317.9122.94 Weight at 350 d, kg437.75**18.63420.5617.12417.82*15.38433.9319.60 Daily gain from 150 to 250 d, kg1.3600.1901.3620.1301.4000.1601.3540.170 Daily gain from 150 to 350 d, kg1.3910.1401.3720.1101.4180.1101.3780.140 Daily gain from 250 to 350 d, kg1.4330.2201.3840.1701.4420.1801.4100.210 Referees score5.6170.7605.8000.8105.6690.7905.6880.790 aBy convention; * designates P< 0.05 and ** designates P< 0.01. bSD designates standard deviation.

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The INRA 11 microsatellite (chromosome 1) presents Allele 1 in subjects that are significantly superior to the rest of the population in growth, hindquarter development and evaluation of the referees.

Instead Allele 6 characterizes subjects with lower growth rate, larger head and negative referee evaluation (Tab. III). In particular, the growth rate of subjects with Allele 1 surpasses that of subjects with Allele 6 by more than 12%.

The INRA 16 microsatellite (chromosome 27) was present with Alleles 7 and 8 in animals with good hindquarter development and with Allele 9 in the subjects with greater growth and more positive referee evaluation (Tab. IV); instead Allele 10 determines lower growth rate (13% less than Allele 9).

The case of the INRA 64 microsatellite (chromosome 23) is very unusual; it has no alleles with positive significance but it is interesting due to Allele 3, present in subjects with a significantly reduced development (P < 0.05 or P < 0.01, depending on the measurements) of nearly all parameters and even P < 0.001 for chest width (Tab. V).

The ETH 131 microsatellite (chromosome 21) reproposes the reduced somatic development with the allele 10 but characterizes good growth with allele 8 and positive referee evaluation with allele 7 (Tab. VI).

Genomic formula of each subject was examinated in order to obtain information about the number of alleles significantly associated with either positive or negative morphological expressions regard- ing meat production. This led to dividing the subjects into three subpopulations: one consisting of 12 individuals with a large number of positive alleles; another, of 7 subjects, with a marked prevalence of negative alleles. the last group of subjects (the largest) presents nearly the same number of positive and negative alleles (data not shown).

The allele frequencies were calculated and the genetic distances estimated for the two subpopulations that were farthest apart. All methods (Nei, 1972; Edwards, 1971, 1974; Cavalli Sforza &

Edwards, 1967) indicated that the two groups of subjects were significantly distant from each other, with a value of 0.365 (Tab. VII) according to the arc distance method of Cavalli Sforza and Edwards (1967).

Hardy-Weinberg proportions (Table VIII) were not respected by any microsatellite of the positive subjects nor by three of the negative

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Tab. III.Somatic measuraments of animals evidencing alleles at locus D1S6 (INRA11) associatedawith beef characters. Subjets withOtherSubjets withOther allele 1subjetsallele 6subjets MeanSDbMeanSDMeanSDMeanSD Height at withers, cm118.291.90118.272.06117.762.13118.721.84 Height at pelvis, cm126.031.75126.031.86125.521.70126.481.84 Depth of chest, cm61.051.0661.051.1260.741.0261.321.11 Body lenght, cm141.522.96141.523.13140.662.86142.283.11 Chest lenght, cm76.881.0076.881.0676.590.9777.141.06 Lenght of rump, cm50.220.8150.220.8549.990.7850.430.85 Width of brisket, cm40.430.4940.230.9240.170.9140.340.83 Width of chest, cm43.900.4543.730.8343.740.7643.770.81 Fore width of rump, cm43.180.9843.181.0442.890.9543.431.03 Medium width of rump, cm45.710.5945.441.0945.371.0745.571.01 Hind width of rump, cm39.000.4638.740.9538.720.9338.840.88 Lenght of head, cm44.001.9143.481.2643.271.0843.801.55 Crest girth, cm183.041.32182.073.08182.162.98182.262.89 Fore cannon girth, cm18.840.3418.880.3518.800.3218.920.36 Buttock girth, cm144.71*6.68139.665.25139.835.54141.005.96 Weight at 150 d, kg159.986.60161.325.76159.875.87162.225.68 Weight at 250 d, kg316.8820.46315.4023.31310.3019.85320.3024.39 Weight at 350 d, kg431.5319.02431.5320.12426.0018.38436.4019.99 Daily gain from 150 to 250 d, kg1.534**0.1001.3300.1601.3420.1301.3780.200 Daily gain from 150 to 350 d, kg1.548***0.1201.3550.1101.341*0.1001.4220.150 Daily gain from 250 to 350 d, kg1.565*0.2201.3890.1901.340*0.1601.4810.220 Referees score6.278*0.7605.5960.7505.430*0.7105.9190.780 a By convention; * designates P< 0.05, ** designates P< 0.01 and *** designates P< 0.001. bSD designates standard deviation.

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Tab. IV.Somatic measuraments of animals evidencing alleles at locus D27S20 (INRA16) associatedawith beef characters. Subjets withOtherSubjets withOther allele 8subjetsallele 9subjets MeanSDbMeanSDMeanSDMeanSD Height at withers, cm118.311.28118.262.15118.21.63118.282.09 Height at pelvis, cm125.921.01126.051.96125.91.15126.051.93 Depth of chest, cm60.980.6161.061.1860.970.6961.061.16 Body lenght, cm141.341.71141.563.30141.321.94141.563.25 Chest lenght, cm76.820.5876.891.1276.810.6676.891.10 Lenght of rump, cm50.170.4750.230.9050.170.5350.230.89 Width of brisket, cm40.150.5240.280.9340.610.6140.200.90 Width of chest, cm43.720.3343.760.8544.080.6943.700.79 Fore width of rump, cm43.120.5743.191.1043.110.6443.191.08 Medium width of rump, cm45.270.7645.521.0845.950.5445.391.08 Hind width of rump, cm38.590.6838.820.9339.250.4638.700.93 Lenght of head, cm43.750.4943.510.2243.290.7643.601.45 Crest girth, cm181.552.30182.353.02183.981.43181.912.99 Fore cannon girth, cm18.820.1918.880.3818.820.2418.880.36 Buttock girth, cm144.38*5.34139.595.521405.48140.585.86 Weight at 150 d, kg162.806.41160.775.74158.435.59161.595.81 Weight at 250 d, kg312.3013.81316.3024.21317.0413.14315.3724.11 Weight at 350 d, kg430.3510.99431.7821.21430.2312.48431.7620.88 Daily gain from 150 to 250 d, kg1.370.171.360.171.495*0.091.340.17 Daily gain from 150 to 350 d, kg1.380.181.390.121.477*0.121.370.13 Daily gain from 250 to 350 d, kg1.380.311.420.181.4530.221.410.21 Referees score5.800.715.660.806.32*0.835.570.72

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Tab. IV.Somatic measuraments of animals evidencing alleles at locus D27S20 (INRA16) associatedawith beef characters. (continued) Subjets withOtherSubjets withOther allele 7subjetsallele 10subjets MeanSDMeanSDMeanSDMeanSD Height at withers, cm117.501.65118.452.07118.332.38118.231.82 Height at pelvis, cm125.801.36126.081.93126.192.15125.941.64 Depth of chest, cm60.910.8261.081.1661.141.3060.990.99 Body lenght, cm141.143.29141.613.25141.793.63141.372.77 Chest lenght, cm76.750.7876.911.1076.971.2376.830.94 Lenght of rump, cm50.120.6250.250.8950.300.9950.180.76 Width of brisket, cm40.160.7140.290.9140.181.0140.310.79 Width of chest, cm43.550.6143.800.8243.641.0143.820.63 Fore width of rump, cm43.050.7643.211.0843.271.2143.130.92 Medium width of rump, cm45.550.8745.461.0845.401.1245.521.00 Hind width of rump, cm38.870.7638.760.9338.690.9738.830.86 Lenght of head, cm43.781.5643.501.3343.471.5043.601.30 Crest girth, cm182.632.52182.123.00181.823.17182.442.77 Fore cannon girth, cm18.830.2618.880.3718.940.3918.830.32 Buttock girth, cm141.29**4.79140.345.97139.005.79141.335.66 Weight at 150 d, kg156.505.68162.215.38161.555.59160.885.46 Weight at 250 d, kg317.8216.69315.1024.07317.2526.34314.6920.81 Weight at 350 d, kg429.1014.69432.1120.90433.2723.30430.5517.80 Daily gain from 150 to 250 d, kg1.450.131.340.171.28**0.191.410.14 Daily gain from 150 to 350 d, kg1.390.131.380.131.340.101.410.14 Daily gain from 250 to 350 d, kg1.300.201.440.201.420.181.410.22 Referees score5.660.435.690.855.410.835.850.70 a By convention; * designates P< 0.05 and ** designates P< 0.01. bSD designates standard deviation.

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Tab. V.Somatic measuraments of animals evidencing alleles at locus D23S15 (INRA64) associatedawith beef characters. Subjets withOther allele 1subjets MeanSDbMeanSD Height at withers, cm116.42**1.37118.771.88 Height at pelvis, cm124.89*1.39126.331.82 Depth of chest, cm60.36*0.8461.231.10 Body lenght, cm139.61*2.34142.043.07 Chest lenght, cm76.23*0.7977.051.04 Lenght of rump, cm49.70*0.6450.360.84 Width of brisket, cm39.51**0.6040.460.82 Width of chest, cm43.07***0.4643.940.75 Fore width of rump, cm42.55*0.7843.351.02 Medium width of rump, cm44.75*0.8245.671.00 Hind width of rump, cm38.16*0.7138.950.87 Lenght of head, cm43.901.1043.461.43 Crest girth, cm180.32*2.32182.732.85 Fore cannon girth, cm18.64*0.2718.930.34 Buttock girth, cm140.895.23140.395.95 Weight at 150 d, kg156.60**4.74162.345.53 Weight at 250 d, kg305.7518.47318.2823.22 Weight at 350 d, kg419.26*15.07434.8519.72 Daily gain from 150 to 250 d, kg1.3720.1201.3580.180 Daily gain from 150 to 350 d, kg1.3740.1101.3870.140 Daily gain from 250 to 350 d, kg1.3770.2001.4250.210 Referees score5.5510.7905.7220.780 aBy convention; * designates P< 0.05, ** designates P< 0.01 and *** designates P< 0.001. bSD designates standard deviation.

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Tab. VI.Somatic measuraments of animals evidencing alleles at locus D21S4 (ETH 131) associatedawith beef characters. Subjets withOtherSubjets withOther allele 8subjetsallele 10subjets MeanSDbMeanSDMeanSDMeanSD Height at withers, cm117.982.08118.322.03116.88*1.60118.512.00 Height at pelvis, cm126.071.78126.021.85124.61*1.31126.271.80 Depth of chest, cm61.071.0761.041.1260.19*0.7961.201.08 Body lenght, cm141.593.00141.513.12139.13*2.21141.943.03 Chest lenght, cm76.901.0276.871.0676.07*0.7577.021.03 Lenght of rump, cm50.240.8250.220.8549.57*0.6050.340.83 Width of brisket, cm40.330.7540.250.9039.58*0.6940.380.85 Width of chest, cm43.730.5243.760.8243.350.5743.830.80 Fore width of rump, cm43.201.0043.181.0442.38*0.7343.321.01 Medium width of rump, cm45.710.9845.441.0544.56**0.8445.640.99 Hind width of rump, cm39.000.8338.740.9138.00**0.7338.920.85 Lenght of head, cm43.710.9543.531.4343.001.1543.651.39 Crest girth, cm183.022.65182.072.95179.84*2.41182.632.80 Fore cannon girth, cm18.940.2618.860.3618.57**0.2518.930.34 Buttock girth, cm144.504.64139.835.69138.005.89141.005.67 Weight at 150 d, kg157.947.27161.685.46161.284.88161.096.04 Weight at 250 d, kg319.7221.38314.9023.12296.75*15.35318.9222.29 Weight at 350 d, kg431.9919.32431.4520.07416.16*14.20434.2219.48 Daily gain from 150 to 250 d, kg1.490*0.1001.3380.1701.232*0.1601.3830.160 Daily gain from 150 to 350 d, kg1.476*0.1201.3680.1301.3300.1501.3940.130 Daily gain from 250 to 350 d, kg1.4580.2201.4080.2101.4610.2001.4070.210 Referees score5.9190.6305.6430.8005.7040.9205.6810.760 a By convention; * designates P< 0.05 and ** designates P< 0.01. bSD designates standard deviation.

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subjects. Also, few microsatellites were in clear disequilibrium. A greater significance for the coefficients of heterozygotes deficiency confirms the tendency toward homozygosis.

The calculation of genetic similarity performed according to the method of Ciampolini et al. (1995) indicates a great homogeneity in the group of subjects with alleles less implicated in meat traits (coefficient of similarity within the population equivalent to 0.430) compared to the subjects with positive alleles (similarity coefficient = 0.359, Table VIII).

DISCUSSION

In a previous study (Ciampolini et al., in press) we undertook to investigate the relationships between the morpho-functional typology of Piemontese beef cattle and the Individual Multilocus Genotype (Ciampolini et al, 1995) determined by means of DNA microsatellites.

This work continues our investigation of the same problem, analyzing the relationships between DNA microsatellites (and their alleles) and the morpho-functional traits of young Piemontese bulls.

Similarly, in the same breed, several authors (Charlier et al., 1995;

Grobet et al., 1997), by means of linkage analysis, have demonstrated the relation between double muscling trait and locus mh (muscular hypertrophy), located on BTA 2. A positional candidate approach sub-

Table VII. Genetic distances between and within furthermost subpopulations Genetic distances

Methods between POS^a within within

and NEG^b POS NEG

Nei (1972) 0.211 - -

Edwards (1971, 1974) 0.424 - -

Cavalli-Sforza and Edwards (1967) 0.365^c - -

Cavalli-Sforza and Edwards (1967) 0.373^d - -

Ciampolini et al., (1995) 0.364 0.359 0.43

a POS designates positive subpopulation; ^bNEG designates negative subpopulation;^c 0.365 = chord distance; ^d0.373 = arc distance.

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Tab. VIII.Hardy-Weinberg proportions and coefficients for heterozygotes deficiency for subjects with a high number of alleles associatedawith positive or negative beef characters. MarkerHardy-Weinberg proportionsbCoefficients for heterozygote deficiencyc. POSdNEGeUNCfPOSNEGUNC INRA50.1370.6170.0780.325**0.322**-0.024 INRA60.9000.955*0.0070.1030.114-0.019 INRA110.2480.955*0.0290.0730.114-0.070 INRA130.3820.2100.863-0.275**-0.487***-0.082 INRA160.7260.7380.6400.0680.379**-0.153 INRA230.9310.5800.3620.0410.000-0.154 INRA250.020*0.6990.7480.0450.000-0.089 INRA270.1180.8430.683-0.352**-0.133-0.210 INRA310.7590.9310.1370.1730.219*-0.057 INRA320.8440.993**0.0910.0560.040-0.149 INRA350.2530.004**0.168-0.195*-0.629***-0.377 INRA370.000***0.1600.000-0.203*-0.226*-0.429 INRA500.0590.1600.207-0.248*-0.015-0.239 INRA530.5620.5820.0290.070-0.015-0.114 INRA630.6840.7860.002-0.241*0.020-0.107 INRA640.019*0.042*0.509-0.418***-0.278**-0.262 INRA720.7530.6970.000-0.072-0.257**-0.004 ETH 1310.8460.020*0.0730.095-0.388***0.034 ETH 1520.2410.7400.7460.000-0.0580.200 ETH 2250.1970.2160.007-0.0370.264*-0.033 a By convention; * designates P< 0.05, ** designates P< 0.01 and *** designates P< 0.001. b0.000 = full disequilibrium; 1.000 = full equilibrium; cvalues below zero = heterozygotes deficiency; dPOS = positive sobpopulation; e NEG = negative subpopulation; fUNC = uncertain subpopulation.

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sequently allowed to identifying an exon 3 missense mutation of myostatin gene as the cause of double muscling in Piemontese cattle breed (Kambadur et al., 1997; McPherron et al., 1997; Smith et al., 1997).

In this study many microsatellites (18 of 20) presented alleles which were significantly linked to somatic measurements more or less relevant to meat production; however only five markers merit further attention since they are present with one allele in more developed individuals and with other alleles in less-developed subjects.

In spite of the aforementioned doubts and uncertainties attending the association of a quantitative trait, such as a somatic measurement or weight gain, to a single marker, the presence of many traits with variability linked to the same alleles appears to confirm that it is no accidental phenomenon. Therefore it also confirms (statistically, as well) the real distance of the population of subjects carrying that allele from those which do not.

Although we propose further investigation of the problem, the results of this study confirm the validity of our methodology, which allowed us to identify several microsatellites which appear to be associated with the production performance of beef cattle. This was reflected in:

• Significant differences between the subpopulation of subjects carrying a certain allele and the subpopulation of carriers of other alleles.

• The consistency between a certain genotype and the phenotypi- cal results (positive or negative) for meat production traits.

• The genetic similarity between subjects corresponding less to the meat typology and the dissimilarity between the ones corresponding more closely to it.

This last observation confirms a previous study’s results (Ciampolini et al., 2001) attributed to the persistence of a base population which remains homogeneous; at the same time, however, the population seems to contain certain “peaks” of advanced selection.

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