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Terje Raudsepp, PhD, Texas A and M University
Michelle Kutzler, DVM, PhD, Oregon State University
Polina Perelman, PhD, NCI, National Institutes of Health
Many reproduction, and fertility related disorders in alpacas and other camelids are caused by structural and numerical changes in chromosomes. At the same time, chromosome analysis in alpacas lags far back the clinical cytogenetics studies in other domestic species. This is because the karyotypes of all camelids are difficult, having high diploid chromosome number (n=74) with no distinct banding or morphological features that can be effectively used to tell chromosomes apart. Furthermore, there is no internationally accepted chromosome nomenclature for the alpaca, and this essentially complicates efficient cross-talk between research groups. Most importantly and in contrast to cattle, horses, pigs and dogs, there are currently no molecular tools for chromosome identification and characterization of chromosomal rearrangements in alpacas or other camelids. Therefore, the goal of this research project was to generate new DNA-based molecular tools for alpaca clinical cytogenetics and validate their utility in the analysis of chromosome abnormalities affecting reproduction and fertility. Extensive clinical cytogenetic studies were carried out by analyzing chromosomes of over 51 alpacas/llamas with various reproduction related disorders. Chromosome abnormalities were detected in 23.5% of the animals, of which the most frequent was the minute chromosome syndrome. Additionally, an autosomal translocation was found in a sterile male llama. Our studies showed that while conventional cytogenetic methods can be used to determine the overall chromosome number and the presence or absence of the minute or a translocation, these methods are not suitable for understanding the nature of these aberrations or their effect on the fertility and reproduction of alpacas. Therefore, a whole-genome set of molecular markers distributed on 30–alpaca chromosomes, including the sex chromosomes, was generated. The utility of these molecular markers was validated in experiments showing that part of the translocation in the sterile male llama was chromosome 20 - a chromosome that carries major histocompatibility complex genes and is essential in innate and acquired immunity. No molecular markers are, as yet, available for the minute chromosome.
Summary. Chromosome abnormalities are a recognized cause for reproductive disorders in alpacas, and it is recommended to continue and expand cytogenetic survey in the breeding populations. Due to the difficulties to analyze camelid chromosomes using conventional cytogenetic methods, introduction of molecular approaches are necessary. The main achievement of this research project is the generation of a unique molecular tool a whole-genome marker map — for alpaca clinical cytogenetics. The molecular complexity of the minute chromosome syndrome, its severe effect on fertility, and the relatively high incidence in alpaca populations, require further research.