Reciprocal translocations in cattle: frequency estimation

Abstract

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 -

De novo Reciprocal Translocation t(5;6)(q13;q34) in Cattle: Cytogenetic and Molecular Characterization

“…Using the banding techniques, a comparison of the abnormal chromosomes against the standard karyogram enabled the definition of the cytogenetic bands involved in the anomaly: 5q13 and 6q34. Once again, the 2 breakpoints were found to be located in the telomeric and centromeric regions as expected in this case [De Lorenzi et al, 2012]. Considering the results reported by De Lorenzi et al [2012], theoretically only onehalf of the RCPs involving BTA5 and BTA6 would produce a derivative longer than BTA1 or shorter than BTA29.…”

“…Once again, the 2 breakpoints were found to be located in the telomeric and centromeric regions as expected in this case [De Lorenzi et al, 2012]. Considering the results reported by De Lorenzi et al [2012], theoretically only onehalf of the RCPs involving BTA5 and BTA6 would produce a derivative longer than BTA1 or shorter than BTA29. On the other hand, considering that the human eye is incapable of detecting small changes in the chromosome length, this value decreases to about a quarter (26.3%) even with an experienced operator.…”

“…This difference in the distribution of breakpoints along entire chromosomes is not linked to the phenotype observed but is a result of the detailed investigation that hypo-fertile subjects undergo [De Lorenzi et al, 2012]. These subjects are always studied with banding techniques that allow for highlighting RCPs even without the presence of an abnormal sized chromosome.…”

The Utility of Chromosome Microdissection in Clinical Cytogenetics: A New Reciprocal Translocation in Sheep

“…So far, centric fusions in sheep are more frequent than reciprocal translocations, while in human newborns the frequency of these anomalies is quite similar. In cattle, only 16% of all reciprocal translocations can be detected by analyzing the conventional karyotype, and, consequently, the real frequency could be 5 times higher than de novo Robertsonian translocations [De Lorenzi et al, 2012]. It is important to remember that chromosomal abnormalities are one cause of economic loss in the animal production.…”

Cytogenetic Elaboration of a Novel Reciprocal Translocation in Sheep

“…In cattle, only 16% of all reciprocal translocations can be detected by analyzing the conventional karyotype and, consequently, the real frequency could be 5 times higher than de novo Robertsonian translocations [De Lorenzi et al, 2012].…”