An investigation of a centric fusion (Robertsonian) translocation of sheep

Long, Susan Elizabeth (1975) An investigation of a centric fusion (Robertsonian) translocation of sheep. PhD thesis, University of Glasgow.

Abstract

The thesis is divided into nine sections. Section I presents a review of the important developments in the field of cytogenetics applicable to the investigations. In this context, the mechanisms involved in leucocytes to cultures were discussed, together with theories concerning the mode of formation of differential staining patterns on chromosomes. Also included in Section I is a review of veterinary cytogenetics which emphasized the relative importance of centric fusion translocations in domestic animals. Section II concerns the examination of the chromosome complement of pre-implantation blastocysts, Blastocysts were collected both from heterozygous male x normal female and normal male x heterozygous female matings. The majority of collections took place post mortem but collection from the live animal by laparotomy was investigated. Information on sex ratio and translocation segregation was obtained from this work. Section III describes the effect, on lambing performance, of heterozygosity for the Massey I translocation in the male. Information was obtained on lambing percentage and ineidence of abortion and stillbriths. In addition, sex ratio and translocation segregation in the live-born lambs were oalculated. Section IV is concerned with male meiosis. Preparations were made from a normal ram and rams hotero and homo for the Masey I translocation. The degree of non at the ecomo meiotic Section V describes the identification of the individual chromosomes comprising' the Massey I translocation. Identification was by means of G-bands and as a corollary of this a G-band idiogram was produced for sheep chromosomes. The Massey I translocation was further categorised by means of c-banding. Section VI is the tables, VII an appendix which describes in more detail some of the routine and less important procedures, VIII is the list of references and Section IX the figures. The work represents the first extensive study of a centric fusion translocation in one of the larger domestic animals. It is argued that whilst the results from the examination of individual aspects of the problem were in themselves inconclusive, collectively, they demonstrated that in the male, heterozygosity for the Massey I translocation did not result in a reduced fertility. Examination of pre-implantation blastocysts failed to reveal zygotes with an unbalanced karyotype and no other chromosomal abnormalities were detected. Examination of lambing performance showed no deviation from the normal sex ratio or the expected translocation segregation ratios, Meiotic studies did show, however, that non-disjunction was occurring at a higher level than in the normal ram and that it was associated with the translocation chromosome. The question remained, therefore, as to whether the unbalanced secondary spermatocytes failed to develop to spermatozoa, or whether, on maturation, they were incapable of fertilisation. The Massey I translocation was identified as a 4/26 translocation by comparison with the G-band idiogram, C-band staining showed that there were two blocks of centromeric heterochromatin, one on either side of the centromere, indicating little or no loss of DNA. It was stressed however, that this could not be taken, per to indicate retention of both centrorneres. It was suggested that a better understanding of the structure of the centromere of centric fusion translocations. would lead to a better understanding of the likely behaviour of such chromosomes during cell division. This would enable a more accurate predication to be made of the effect on fertility.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Animal sciences
• Date of Award: 1975
• Depositing User: Enlighten Team
• Unique ID: glathesis:1975-72671
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 11 Jun 2019 11:06
• Last Modified: 11 Jun 2019 11:06
• URI: https://theses.gla.ac.uk/id/eprint/72671