Application of Molecular Cytogenetic Tools in Camelids: Characterization of an Autosomal Translocation in an Infertile Llama

Balanced autosomal translocations have been associated with reduced fertility and infertility in humans, mice and livestock species. Such translocations typically do not affect the health or viability of the carrier, but disturb chromosome pairing and segregation during gametogenesis, resulting in the formation of both genetically balanced and unbalanced gametes. Here we describe the case of a 10-year old male llama (Lama glama) referred for chromosome analysis due to infertility. Clinical examination showed that 75% of his sperm had morphologic defects (midpiece defects, nuclear and acrosomal vacuoles), whereas the testes and accessory glands appeared normal upon ultrasound. Conventional cytogenetic analysis revealed an abnormal 73,XY karyotype with an autosomal translocation (normal diploid number in camelids is 2n=74). The derivative chromosome, as determined by G-banding, was submetacentric with size and morphology similar to chrX. Molecular cytogenetic analysis using probes specific to chrX and chrY showed that both sex chromosomes were normal. Further FISH analysis with a set of camelid autosome-specific probes revealed that the short arm of the derivative chromosome corresponded to chr20, and the long arm to chr12. Camelid chr20 is homologous to human chr6p and carries the MHC, whereas camelid chr12 corresponds to parts of human chrs12 and 22. Subsequent studies are needed to identify the genes affected by the translocation and whether any of the genes have functions in spermatogenesis. This first case of a translocation ever reported in a camelid species demonstrates effective use of the molecular cytogenetic tools only recently available for these species.