Genetic relationships between Spanish Assaf (Assaf.E) and Spanish native dairy sheep breeds

At present, the Assaf is the main dairy sheep in Spain. The Spanish Assaf (Assaf.E) was formed by male-mediated absorption of native Spanish sheep. Here we assess the genetic relationships among the Assaf.E and major native Spanish dairy breeds using microsatellites to contribute to the knowledge of the formation and within-population genetic variability of the breed. Blood samples from 44 unrelated Assaf.E individuals from 23 different Assaf.E flocks spread throughout 6 different Spanish provinces were obtained and genotyped using 14 microsatellites. Up to 312 additional samples belonging to the Awassi and Milchschaf sheep breeds and to six native Spanish dairy sheep breeds (Castellana, Churra, Latxa, Manchega, and Rubia de El Molar) as well as samples from Merino individuals to be used as the outgroup were also analysed observed (H_o) and expected (H_e) heterozygosity, rarefacted number of alleles per locus and distances based on molecular coancestry information were computed. Probabilities of assignment of the Assaf.E individuals to native Spanish dairy sheep breeds and cryptic genetic structure in the whole dataset were also assessed. It can be concluded that the Assaf.E breed has low genetic variability and high genetic distance with respect native Spanish dairy sheep breeds. From our results, the formation of the Assaf.E breed basically occurred via the absorption of individuals belonging to the Entrefino type, particularly to the Castellana and Manchega populations. Furthermore, Churra individuals may have participated in the formation of the Assaf.E breed at an early moment of the introduction of the breed into Spain.     

Genetic relationships between Spanish Assaf (Assaf.E) and Spanish native dairy sheep breeds

At present, the Assaf is the main dairy sheep in Spain. The Spanish Assaf (Assaf.E) was formed by male-mediated absorption of native Spanish sheep. Here we assess the genetic relationships among the Assaf.E and major native Spanish dairy breeds using microsatellites to contribute to the knowledge of the formation and within-population genetic variability of the breed. Blood samples from 44 unrelated Assaf.E individuals from 23 different Assaf.E flocks spread throughout 6 different Spanish provinces were obtained and genotyped using 14 microsatellites. Up to 312 additional samples belonging to the Awassi and Milchschaf sheep breeds and to six native Spanish dairy sheep breeds (Castellana, Churra, Latxa, Manchega, and Rubia de El Molar) as well as samples from Merino individuals to be used as the outgroup were also analysed observed (H_o) and expected (H_e) heterozygosity, rarefacted number of alleles per locus and distances based on molecular coancestry information were computed. Probabilities of assignment of the Assaf.E individuals to native Spanish dairy sheep breeds and cryptic genetic structure in the whole dataset were also assessed. It can be concluded that the Assaf.E breed has low genetic variability and high genetic distance with respect native Spanish dairy sheep breeds. From our results, the formation of the Assaf.E breed basically occurred via the absorption of individuals belonging to the Entrefino type, particularly to the Castellana and Manchega populations. Furthermore, Churra individuals may have participated in the formation of the Assaf.E breed at an early moment of the introduction of the breed into Spain.     

Utilization of frozen-thawed epididymal ram semen to preserve genetic diversity in Scrapie susceptible sheep breeds

The European Union has introduced transmissible spongiform encephalopathy (TSE) resistance breeding programmes for several sheep breeds to cope with the genetic susceptibility to Scrapie infections. Due to the different allele frequencies among breeds, strong selection for ARR alleles is associated with a loss of genetic diversity in small populations and in larger populations with unfavourable ARR allele frequencies. To ensure maintenance of genetic diversity, an adhoc cryopreservation programme was initiated employing epididymal sperm from 109 rams representing 16 different breeds within one breeding season. Epididymal semen was chosen for this adhoc programme because time consuming training of rams for ejaculated semen collection via an artificial vagina was not possible. Prior to freezing, average sperm motility was 79.7% and acrosome integrity was 93.7%. After freezing, these levels were decreased to 60.5 and 72.8%, respectively. An insemination trial using frozen-thawed epididymal semen resulted in a lambing rate of 87.5%. Results show that this semen preservation method is robust and efficient and associated with high fertility. It may also be useful for other animal species.     

The PrP genotype of sheep of the improved Valachian breed

In a worldwide majority of sheep breeds an excessive susceptibility to scrapie associated with the PrP gene alleles coding for valine (V; at the 136 codon) and glutamine (Q; at the 171 codon) (e.g., VRQ/VRQ, VRQ/ARQ, or ARQ/ARQ) was demonstrated. Particularly the PrPVRQ allele is closely associated with the high-risk development of the disease; the PrPARQ allele can also fulfill this function but under certain limited conditions. Polymorphism in the PrP gene sequences (conclusively related to the increased susceptibility of sheep to scrapie) of improved Valachian sheep from two Slovak regions, Orava and Spis, was determined. Examination of 735 sheep showed that ARR/ARQ was the most frequent genotype (45.2%). High-risk genotypes were determined in 32.4% of sheep (ARQ/ARQ 19.3, ARR/VRQ 9.0, ARR/VRQ 3.5, VRQ/VRQ 0.3, ARR/VRR 0.3). Low-risk genotypes were found in 67.7% of sheep (ARR/ARQ 45.2, ARR/ARR 10.9, ARR/AHQ 5.7, ARQ/ARQ 4.9, AHQ/AHQ 0.7, ARR/AHR 0.3). Despite the geographically distant flocks of improved Valachian sheep investigated no difference in the occurrence of individual PrP genotypes was observed.     

新疆地区绵羊品种朊蛋白基因136、154和171位点的多态性

绵羊痒病是一种渐进性和致死性中枢神经系统疾病,绵羊朊蛋白基因(Prion protein gene,PRNP)多态性与痒病的易感或抗性有关,其中PRNP136位(V/A)、154位(H/R)和171位(H/Q/R)的基因多态性与该病发生最相关。为评价新疆地区主要绵羊品种对痒病的易感性,文章对新疆地区10个绵羊品种(阿勒泰、巴士拜、巴音布鲁克、多浪、和田、策勒黑、中国美利奴、德国肉用美利奴、特克赛尔和萨福克羊)共746只个体PRNP基因的136位(V/A)、154位(H/R)和171位(H/Q/R)的遗传多态性进行分析,检测到了ARQ、ARR、ARH、ARK、VRQ、AHR、AHQ、AHH8种等位基因,其中ARQ和ARR等位基因存在于所有品种中,且ARQ在所有品种中的基因频率最高。ARH存在于除萨福克和德国肉用美利奴羊外的8个绵羊品种中。仅在新疆地方品种阿勒泰、巴音布鲁克、巴士拜和多浪羊中检测到ARK等位基因。而VRQ、AHR、AHQ和AHH4种等位基因只在中国美利奴羊上存在,且频率极低。在10个品种中共检测到了ARQ/ARQ、ARQ/ARK、ARR/ARR、ARH/ARH、ARQ/ARR、ARH/ARQ、ARH/ARR、ARK/ARK、ARH/ARK、ARQ/VRQ、ARQ/AHQ、ARQ/AHR和ARH/AHH13种基因型,其中中度易感的ARQ/ARQ基因型频率最高,而抗性最强的ARR/ARR基因型仅存在于巴音布鲁克、策勒黑、中国美利奴、特克赛尔和德国肉用美利奴羊,且频率较低。文章首次在中国美利奴羊上发现了易感性很强的VRQ/ARQ基因型。上述结果提示新疆的主要绵羊品种对痒病的抗性较弱。     

Prion protein (PrP) gene polymorphism in Red Maasai and Black Head Persian sheep breeds in Tanzania: Consistent profile regardless of locations

The status of scrapie in Africa is largely unknown. The susceptibility to scrapie and its pathology is determined by amino acid polymorphisms at positions 136 (A/V), 154 (R/H) and 171 (Q/R/H) of the ovine PrP gene (PrP genotype) of the animals. Despite the widely studied PrP gene polymorphisms worldwide, limited data is available on PrP genotypes of sheep from the African continent. Previously, we have reported six PrP genotypes derived from four different alleles in Red Maasai and Black Herd Persian (BHP), the ARQ/ARQ genotype being more frequent in the Red Maasai than in the BHP sheep. The highly susceptible VRQ allele was not found in any of the sheep breeds; the ARR allele was absent in the Red Maasai or occurred at a low frequency in the BHP. The lack of the highly susceptible VRQ alleles among Tanzanian sheep examined, necessitated further examinations on genetic susceptibility in sheep of the same breeds, but originating from an entirely different part of Tanzania. Consistently, ARQ/ARQ genotype was observed in 88% of Red Maasai and 64% of BHP sheep, ARQ/AHQ genotype was present in 12% in Red Maasai and 36% in BHP. Neither the highly resistant (ARR/ARR), nor the highly susceptible (VRQ/VRQ) genotypes were found. The ARQ and AHQ were the only alleles observed. The ARQ allele constituted 94%, 82% and 67% in the Red Maasai, BHP and cross-bred sheep, respectively. The AHQ constituted 6%, 18% and 33%, respectively. Data reported here, provide additional information on genetic susceptibility of the Red Maasai, BHP and their crosses; they may be helpful in policy formulation for future prevention of scrapie.     

Prion protein gene polymorphisms in sheep in the state of Paraná, Brazil

To determine the polymorphisms of the prion protein gene in sheep from the state of Paraná, Brazil, 323 animals of meat breeds (Suffolk, Hampshire Down, Texel, Ile de France, Dorper, Dorset, Santa Inês and crossbreds) were genotyped by restriction fragment length polymorphism (RFLP) analysis. The most frequent allele was ARQ, with a frequency of 0.61, followed by ARR (0.30). VRQ and AHQ alleles were present at very low frequencies (0.13 and 0.05 respectively), and the ARH allele was not found. Seven genotypes were identified (ARR/ARR, ARR/ARQ, ARQ/ARQ, ARR/VRQ, ARR/AHQ, ARQ/VRQ and ARQ/AHQ), of which ARQ/ARQ was the most frequent (0.41). The Santa Inês breed and crossbred animals showed the highest genotypic variability.     

Prion protein gene (PrP) polymorphisms in healthy sheep in Turkey

Scrapie, a transmissible spongiform encephalopathy (TSE) or prion disease, is a fatal, neurodegenerative disease in sheep and goats. This disease has been known in Europe for more than 250 years. Susceptibility to scrapie is associated with polymorphisms in the sheep prion protein gene (PrP) gene. In sheep, polymorphism in the PrP gene has been identified at a number of codons, and polymorphisms at codons 136, 154 and 171 have reported linkage with susceptibility to scrapie. Polymorphisms at the PrP locus were studied in 413 animals representing three native sheep breeds (Imroz, Chios and Kıvırcık) in Turkey. Genomic DNA was obtained from blood, and genotypes were screened using PCR and direct DNA sequencing. We report 17 genotypes derived from seven different alleles. The most frequent genotype in the Kıvırcık sheep is ARQ/ARQ, whereas the ARR/ARQ genotype is predominant in the Chios and Imroz breeds. In general, the ARQ haplotype was the predominant haplotype. ARQ haplotype was also predominant in the Kıvırcık and Chios sheep breeds, whereas the Imroz sheep predominantly had the ARR haplotype. The susceptibility-associated VRQ haplotype was found in 2.38%, 0.35% and 0.81% of the Imroz, Kıvırcık and Chios sheep, respectively. Moreover, seven additional polymorphisms have been detected at codons G127S, G127V, H143R, G145S, Y172D, N174Y and Q189L. Among these polymorphisms, the N174Y allele is a novel polymorphism, and the G145S allele is a novel allele for a known polymorphic locus.     

Genotyping of the prion protein (PrP) gene in Red Maasai and Black Head Persian sheep in Tanzania

Susceptibility to scrapie in sheep is largely influenced by four polymorphic amino acid positions of the ovine PrP gene at codons 136, 141, 154 and 171. Genotyping of corresponding DNA polymorphism can be used as a basis for selection decisions. A total of 100 Red Maasai and 79 Black Herd Persian sheep, representative of the widely distributed breeds in Tanzania, were genotyped by real-time PCR. Genomic DNA was extracted from buccal epithelial cells. We report six genotypes derived from four different alleles, with the ARQ/ARQ genotype being more frequent (p = 0.0081) in the Red Maasai than in the Black Head Persian sheep. Our study also demonstrated higher allelic frequency (p = 0.00055) of the ARQ in the Red Maasai than in Black Head Persian sheep, while the AHQ allelic frequency was higher (p = 0.00086) in the Black Head Persian. All the animals were homozygous LL₁₄₁. The highly susceptible VRQ allele was not found in any of the sheep breeds examined in this study. Both breeds were genetically low-level resistant to scrapie (NSP3). Due to absence or very low frequency of the ARR allele in the two breeds, selection for genetic resistance to scrapie through an increase of the ARR allele does not seem very relevant. If new breeds of sheep are to be introduced for crossbreeding in Tanzania, care should be taken to avoid import of the VRQ allele. To our knowledge, this is the first study exploring the PrP genotypes in sub-Saharan African sheep and in the Red Maasai and Black Head Persian sheep breeds in particular. The data provide base-line information on genetic susceptibility of the two sheep breeds to scrapie, which may be useful in policy formulation for prevention and future research on prion diseases.     

Genetic diversity of the prion protein gene (<Emphasis Type="Italic">PRNP</Emphasis>) coding sequence in Czech sheep and evaluation of the national breeding programme for resistance to scrapie in the Czech Republic

Of 34 breeds kept in the Czech Republic 45,604 sheep were genotyped for codons 136, 154 and 171 in the prion protein gene (PRNP) during the years 2006–2014. In this cohort, haplotypes ARR, ARQ, ARH, AHQ, VRQ, AHR and ARK were detected. The haplotype AF₁₄₁RQ associated with susceptibility to atypical scrapie was observed in nine out of 30 breeds analysed for this purpose. In addition, six rare nonsynonymous substitutions producing haplotypes AT₁₃₇RQ, AN₁₃₈RQ, AG₁₅₁RQ, AH₁₅₁RQ, ARL₁₆₈Q and ARQE₁₇₅ were identified in various breeds. Due to their low frequencies, these polymorphisms are of no potential importance for the breeding programme. With regard to their genetic particularity, Sumavka, Valachian and Cameroon breeds were screened for additional polymorphisms. Further haplotypes, AR₁₄₃RQ and AS₁₄₆RQ, were found in Sumavka and Cameroon, and in Valachian sheep, respectively. Frequencies of the ARR (resistance-associated), VRQ (susceptibility-associated) haplotypes, and of the most resistant ARR/ARR genotype calculated for sheep born in the years 2001–2003 and 2011–2013 documented effects of the 10 year-lasting national breeding programme. The total frequency of ARR doubled from 36.8 to 75.8 %, while the frequency of VRQ decreased from 4 to 0.7 %. The total frequency of the ARR/ARR genotype increased from 17.7 to 59 %. These data show that the national scrapie resistance breeding programme has had an important desirable effect on haplotype and genotype frequencies of PRNP in Czech sheep.     

Prion Protein Coding Gene (PRNP) Variability in Sheep from Turkey and Iran

This study was designed to analyze variation of ovine prion protein in sheep breeds in Iran and Turkey. A competitive approach was used to analyze the open reading frame (ORF) of the ovine PRNP gene using a total of 186 samples from five indigenous sheep breeds. The ARQ allele was found to be the predominant allele in five breeds. The ARR allele was not observed in homozygous combination among the 11 genotypes found in the study. In addition, six other polymorphisms were indicated. These findings have great significance for estimating genetic variability in the PRNP gene with regard to Iranian and Turkish sheep. Since no information on the susceptibility of some genotypes identified in this study has been reported, no grouping was made on the basis of susceptibility.     

Allele frequency of the spider lamb syndrome in Brazilian Hampshire Down and Suffolk flocks

The spider lamb syndrome (SLS) is an autosomal recessive condition of sheep, characterized by severe bone lesions. The disease is caused by a mutation at codon 700 of the gene fibroblast growth factor receptor 3 (FGFR3), resulting in a valine (V) to glutamate (E) substitution, and leading to an abnormal bone growth. Congenital diseases as SLS may have an important impact on animal production. The objective of this work was to detect the frequency of E allele on Suffolk and H. Down breeds in three flocks from the southern region of Brazil. A total of 256 samples, 146 from two Suffolk flocks and 110 from one H. Down flocks were evaluated. The genomic DNA extracted from peripheral blood was PCR amplified and cleaved with XhoI restriction enzyme. Allele E frequency varied among the different herds: Suffolk, 6% in one flock and 3% in the other, and H. Down 6%, corresponding to 6–12% of heterozygotes for the condition. These results emphasize the need for preventive measures to minimize the birth of affected lambs. Also, the culling of animals, mainly rams, carrying the E allele will bring more efficiency to the sheep industry. These data are important also for sheep breeders, as the genotyping of the breed stock will afford more security to breeding programs and stop the spread of this undesirable allele, reducing economic losses. It is important to note that, in Brazil, the DNA test for SLS is not a routine procedure.     

Allelic frequencies of an ovine scrapie susceptibility gene

Abstract

The allelic frequencies of an ovine gene associated with susceptibility to scrapie was analyzed in a sample of 30 scrapie affected sheep and 545 clinically normal sheep from 12 flocks. The allele encoding glutamine at codon 171 occurred at a frequency of 0.76 in the overall population. All 30 scrapie affected sheep were homozygous for glutamine at codon 171. This genotype was observed in 56.5% of the clinically normal sheep. None of the 30 scrapie affected sheep carried the allele encoding Valine at codon 136 although this allele was observed in 2/12 flocks sampled.     

Associations of PrP genotype with lamb production traits in three commercial breeds of British lowland sheep

The Ram Genotyping Scheme was launched in Great Britain in 2001 as part of the National Scrapie Plan and was devised to reduce and eventually eradicate classical scrapie susceptible genotypes from the national pedigree flock. Anecdotal claims from breeders suggest that sheep with more resistant PrP genotypes may have inferior phenotypes. In this study, we test this possibility for lamb production traits in three breeds of lowland sheep: Charollais (22 752 lambs), Poll Dorset (22 589 lambs) and Texel (23 492 lambs). Data were received from 50 breeders and comprised weights at birth, 8 weeks and scanning (from which average daily weight gain was derived), and ultrasonic muscle and fat depths. Animal (direct) genetic effects and up to three maternal effects were fitted in linear mixed models for each trait. Fitting either PrP genotype or number of copies of individual alleles carried as fixed effects allowed potential associations with the PrP gene to be assessed. There were no significant associations seen in the Poll Dorset breed; however, significant associations were found with the number of allele copies carried in the other two breeds included in this study. Charollais lambs carrying one copy of the VRQ allele had significantly (P < 0.01) greater ultrasonic muscle depth (0.58 mm) and fat depth (0.2 mm) than non-carriers. In the Texel breed, lambs with one ARR allele were significantly heavier than those with two or zero ARR alleles; heterozygous ARR lambs were 0.07 kg heavier at birth (P < 0.05), 0.42 kg heavier at 8 weeks (P < 0.01) and 0.17 kg heavier at scan weight (P < 0.01), than non-carriers. After Bonferroni corrections to adjust significance thresholds to account for the large number of independent comparisons made, all significant results remained so at P < 0.05 or greater, except for the ARR allele effect on birth weight in the Texel breed, which was no longer significant. These results compare favourably with others from studies on many continental breeds of sheep, published in recent years, and add credence to the conclusion that selection on PrP genotype is unlikely to have any noticeable impact on the measured growth and carcass traits in sheep.     

Population structure in Indian sheep ascertained using microsatellite information

This study attempts to provide a comprehensive insight into the prevailing genetic status of Indian sheep breeds using microsatellite markers. Seventeen Indian sheep breeds from 3 agroecological zones were analysed using a panel of 25 microsatellite markers. All of the sheep breeds investigated were genetically diverse, as evident from the high allele (>6) and gene (>0.6) diversity values. The gene diversity values for all breeds ranged from 0.621 to 0.780. The within-population heterozygote deficit (F(IS)) varied from -0.098 to 0.234, reflecting significant levels for 12 of the 17 breeds investigated. The average genetic differentiation between all breeds (F(ST)) was 11.1%, revealing moderate discrimination between the indigenous sheep breeds. The genetic distance and principal component analysis revealed a separation of sheep breeds based on geographical propinquity. The Bayesian clustering approach suggested poor breed differentiation in the north-western arid and semi-arid region when compared to the breeds from the eastern and southern peninsular regions. The observed results mirror the divergent management strategies in the different agroecological regions, lack of specific selection policies, and intermixing of breeds in close proximity. Immediate steps to curb the intermixing and erosion of breed purity for some of these breeds need to be implemented, for example, by introducing measures like making proven rams available and ensuring their frequent exchange between flocks. The data generated here provides valuable information about the genetic structure of the 17 Indian sheep breeds and this can be used for designating priorities for their conservation.     

Review: A review on classical and atypical scrapie in caprine: Prion protein gene polymorphisms and their role in the disease

Scrapie is a naturally occurring transmissible spongiform encephalopathy in sheep and goat. It has been known for ~250 years and is characterised by the accumulation of an abnormal isoform of a host-encoded prion protein that leads to progressive neurodegeneration and death. Scrapie is recognised in two forms, classical and atypical scrapie. The susceptibility to both types of scrapie is influenced by polymorphisms of the prion protein gene (PRNP). Sheep susceptibility or resistance to classical scrapie is strongly regulated by the polymorphisms at codons 136, 154 and 171 of the PRNP. The genetic role in atypical scrapie in sheep has been defined by polymorphisms at codons 141, 154 and 171, which are associated with different degrees of risk in the occurrence of the ovine disease. Progress has been achieved in the prevention of scrapie in sheep due to efficient genetic breeding programmes based on eradication and control of the disease. In Europe, the success of these programmes has been verified by applying eradication and genetic selection plans. In general terms, the ovine selection plans aim to eliminate and reduce the susceptible allele and to enrich the resistant allele ARR. During outbreaks all susceptible animals are slaughtered, only ARR/ARR resistant rams and sheep and semi-resistant females are preserved. In the occurrence of scrapie positive goats a complete cull of the flock (stamping out) is performed with great economic loss and severe risk of extinction for the endangered breeds. The ability to select scrapie-resistant animals allows to define new breeding strategies aimed to boost genetic progress while reducing costs during scrapie outbreaks. Allelic variants of PRNP can be protective for caprine scrapie, and the knowledge of their distribution in goats has become very important. Over the past few years, the integration of genetic information on goat populations could be used to make selection decisions, commonly referred to as genetic selection. The objective of this review was to summarise the main findings of polymorphisms of the caprine prion protein (PrP) gene and to discuss the possible application of goat breeding schemes integrating genetic selection, with their relative advantages and limitations.     

Analysis of prion protein genotypes in relation to reproduction traits in local and cosmopolitan German sheep breeds

Due to the genetic determination of susceptibility to scrapie and other forms of transmissible spongiform encephalopathy (TSE) in sheep breeding to the less susceptible prion protein (PrP) genotype ARR/ARR was advanced within EU. In 4961 ewes of nine German sheep breeds (Coburg Fox sheep, Gray Horned Heath sheep, Merinoland sheep, Rhoen sheep, German Blackheaded Mutton sheep, Shropshire, Suffolk, Texel and White East Friesian Milk sheep) representing local and cosmopolitan breeds the reproductive traits number of lambs born, dead (including abortion at the end of pregnancy, stillbirth and death during the first 56 days post natum), weaned and rearing rate at each lambing were recorded and in 1641 of these ewes the PrP genotype was determined. A linear model was used to evaluate associations between PrP genotype and reproduction traits including the effects of PrP genotype (four classes: ewes with two, one and no copy of the ARR allele and with unknown PrP genotype), breed, interaction of PrP genotype and breed, number of lambing, lambing season and stock. Significant associations were only observed between the PrP genotype and the number of dead lambs at each lambing in Shropshire and Merinoland sheep and the rearing rate at each lambing in Shropshire. These significant associations were mainly caused by differences between animals with unknown PrP genotype and animals of the other PrP classes. In conclusion, breeding for TSE resistant sheep will not lead to a reduction in economically important reproduction traits.     

Blood groups and protein polymorphisms in five goat breeds (Capra hircus)

Data on allele frequencies at six red cell blood group systems and three blood protein polymorphic loci in five goat breeds are reported. Two blood proteins, albumin and carbonic anhy-drase, were not found to be polymorphic. The B blood group system of goats, like its homologue in cattle and sheep, is highly complex. At least 44 B phenogroups (haplotypes) have been distinguished in this study. Based on the variation in allele frequencies between breeds, genetic distances were calculated. The distances estimated by four different methods were in close agreement with data from the history and geographic origins of the breeds examined.     

Genetic relationships among Spanish sheep using microsatellites

Five indigenous Spanish breeds of sheep, Churra, Latxa, Manchega, Rasa–Aragonesa and Merino, with Awassi sheep as a reference breed were genotyped for 19 DNA microsatellites. Allele frequencies and mean heterozygosities revealed the greatest genetic variation in Merino sheep and the lowest in Awassis. Differences in variability were not great in the other breeds studied. The dendrograms obtained based on genetic distances showed a large differentiation between Awassi sheep and the Spanish breeds, as was to be expected from their distinct genetic origin. Merinos appeared separated from the other four breeds, of which, according to a classification based on the fleece characteristics, Churra and Latxa belong to the churro type and Manchega and Rasa–Aragonesa to the so called entrefino type, though no clear separation was evident between the two types. These results suggest that morphological data alone are insufficient for determining relationships between breeds and that studies involving genetic markers may be of great assistance.