Clinical animal cytogenetics development began in the 1960’s, almost at the same time as human cytogenetics. However, the development of the two disciplines has been very different during the last four decades. Clinical animal cytogenetics reached its ‘Golden Age’ at the end of the 1980’s. The majority of the laboratories, as well as the main screening programs in farm animal species, presented in this review, were implemented during that period, under the guidance of some historical leaders, the first of whom was Ingemar Gustavsson. Over the past 40 years, hundreds of scientific publications reporting original chromosomal abnormalities generally associated with clinical disorders (mainly fertility impairment) have been published. Since the 1980’s, the number of scientists involved in clinical animal cytogenetics has drastically decreased for different reasons and the activities in that field are now concentrated in only a few laboratories (10 to 15, mainly in Europe), some of which have become highly specialized. Currently between 8,000 and 10,000 chromosomal analyses are carried out each year worldwide, mainly in cattle, pigs, and horses. About half of these analyses are performed in one French laboratory. Accurate estimates of the prevalence of chromosomal abnormalities in some populations are now available. For instance, one phenotypically normal pig in 200 controlled in France carries a structural chromosomal rearrangement. The frequency of the widespread 1;29 Robertsonian translocation in cattle has greatly decreased in most countries, but remains rather high in certain breeds (up to 20–25% in large beef cattle populations, even higher in some local breeds). The continuation, and in some instances the development of the chromosomal screening programs in farm animal populations allowed the implementation of new and original scientific projects, aimed at exploring some basic questions in the fields of chromosome and/or cell biology, thanks to easier access to interesting biological materials (germ cells, gametes, embryos ...).

During normal cytogenetic investigations on the Chianina cattle (BTA) breed, a normal looking young bull was found to carry an abnormal Y chromosome which was a product of a reciprocal translocation between chromosomes Y and 9. This was revealed by both CBA- and RBG-banding techniques and was clearly confirmed by FISH-mapping analysis with IDVGA50 (which paints the complete Yq arm in a normal Y), as well as with AMD1, CGA, IGF2R (mapping to BTA9q16, BTA9q22 and BTA9q27→q28, respectively) and SRY (mapping to normal BTAYq23). Analysis on sperm from four different samples revealed azoospermia in the carrier, indicating that the rcp(Y;9) induces sterility in the bull.

SummaryChromosomal anomalies, like Robertsonian and reciprocal translocations represent a big problem in cattle breeding as their presence induces, in the carrier subjects, a well documented fertility reduction. In cattle reciprocal translocations (RCPs, a chromosome abnormality caused by an exchange of material between nonhomologous chromosomes) are considered rare as to date only 19 reciprocal translocations have been described. In cattle it is common knowledge that the Robertsonian translocations represent the most common cytogenetic anomalies, and this is probably due to the existence of the endemic 1;29 Robertsonian translocation. However, these considerations are based on data obtained using techniques that are unable to identify all reciprocal translocations and thus their frequency is clearly underestimated.The purpose of this work is to provide a first realistic estimate of the impact of RCPs in the cattle population studied, trying to eliminate the factors which have caused an underestimation of their frequency so far. We performed this work using a mathematical as well as a simulation approach and, as biological data, we considered the cytogenetic results obtained in the last 15 years. The results obtained show that only 16% of reciprocal translocations can be detected using simple Giemsa techniques and consequently they could be present in no less than 0,14% of cattle subjects, a frequency five times higher than that shown by de novo Robertsonian translocations. This data is useful to open a debate about the need to introduce a more efficient method to identify RCP in cattle.-3 -

Robertsonian translocation (rob) involving chromosomes 1 and 29 represents the most frequent chromosome abnormality observed in cattle breeds intended for meat production. The negative effects of this anomaly on fertility are widely demonstrated, and in many countries, screening programs are being carried out to eliminate carriers from reproduction. Although rob(1;29) was first observed in 1964, the genomic structure of this anomaly is partially unclear. In this work, we demonstrate that, during the fusion process, around 5.4 Mb of the pericentromeric region of BTA29 moves to the q arm, close to the centromere, of rob(1;29). We also clearly show that this fragment is inverted. We find that no deletion/duplication involving sequences reported in the BosTau6 genome assembly occurred during the fusion process which originates this translocation.

The oral mucosae of the lips and muzzle appeared histologically normal.Mitotic chromosomes were visualised with conventional staining and RBA-banding from non-synchronised cultures of peripheral blood lymphocytes of the affected calves and their relatives (De Grouchy and others 1964, Dutrillaux and others 1973). No abnormality was detected in either the structure or the number of chromosomes.Genealogical data from the Chianina Breed Stud Book, from the Associazione Nazionale Allevatori Bovini Italiani da Carne (ANABIC), were collected to analyse the pedigrees of the two affected animals and of nine other newborn Chianina calves showing the same condition (Fig 3). Wherever possible, blood samples were collected from the affected animals and their sires, dams and siblings. Parentage relationships were verified by microsatellite analysis with StockMarks for Cattle Paternity PCR typing kits (Applied Biosystems).Forty-nine animals of the familial group were evaluated. Analysis of the pedigree information revealed that all clinical cases were generated by consanguineous matings. In particular, three bulls were acknowledged as being disease carriers: bulls 23, 30 and 34 (Fig 3). Bull 23 sired three affected male calves (26, 28 and 48) and two healthy female calves (31 and 35); bull 30 sired two affected male calves (27 and 49) and two healthy calves, one male (34) and one female (46); and bull 34 sired six affected calves, four males (38, 40, 41 and 47) and two females (43 and 44) and four healthy calves, three males (37, 42 and 45) and one female (39). None of the car-