Generation of an improved cytogenetic and comparative map of Bos taurus chromosome BTA27

Molecular Cytogenetics in Domestic Bovids: A Review

The discovery of the Robertsonian translocation (rob) involving cattle chromosomes 1 and 29 and the demonstration of its deleterious effects on fertility focused the interest of many scientific groups on using chromosome banding techniques to reveal chromosome abnormalities and verify their effects on fertility in domestic animals. At the same time, comparative banding studies among various species of domestic or wild animals were found useful for delineating chromosome evolution among species. The advent of molecular cytogenetics, particularly the use of fluorescence in situ hybridization (FISH), has allowed a deeper investigation of the chromosomes of domestic animals through: (a) the physical mapping of specific DNA sequences on chromosome regions; (b) the use of specific chromosome markers for the identification of the chromosomes or chromosome regions involved in chromosome abnormalities, especially when poor banding patterns are produced; (c) better anchoring of radiation hybrid and genetic maps to specific chromosome regions; (d) better comparisons of related and unrelated species by comparative FISH mapping and/or Zoo-FISH techniques; (e) the study of meiotic segregation, especially by sperm-FISH, in some chromosome abnormalities; (f) better demonstration of conserved or lost DNA sequences in chromosome abnormalities; (g) the use of informatic and genomic reconstructions, in addition to CGH arrays, to predict conserved or lost chromosome regions in related species; and (h) the study of some chromosome abnormalities and genomic stability using PCR applications. This review summarizes the most important applications of molecular cytogenetics in domestic bovids, with an emphasis on FISH mapping applications.

Cytogenetic anchoring of radiation hybrid and virtual maps of sheep chromosome X and comparison of X chromosomes in sheep, cattle, and human

A comprehensive physical map was generated for Ovis aries chromosome X (OARX) based on a cytogenomics approach. DNA probes were prepared from bacterial artificial chromosome (BAC) clones from the CHORI-243 sheep library and were assigned to G-banded metaphase spreads via fluorescence in-situ hybridization (FISH). A total of 22 BACs gave a single hybridization signal to the X chromosome and were assigned out of 32 tested. The positioned BACs contained 16 genes and a microsatellite marker which represent new cytogenetically mapped loci in the sheep genome. The gene and microsatellite loci serve to anchor between the existing radiation hybrid (RH) and virtual sheep genome (VSG) maps to the cytogenetic OARX map, whilst the BACs themselves also serve as anchors between the VSG and the cytogenetic maps. An additional 17 links between the RH and cytogenetic maps are provided by BAC end sequence (BES) derived markers that have also been positioned on the RH map. Comparison of the map orders for the cytogenetic, RH, and virtual maps reveals that the orders for the cytogenetic and RH maps are most similar, with only one locus, represented by BAC CH243-330E18, mapping to relatively different positions. Several discrepancies, including an inverted segment are found when comparing both the cytogenetic and RH maps with the virtual map. These discrepancies highlight the value of using physical mapping methods to inform the process of future in silico map construction. A detailed comparative analysis of sheep, human, and cattle mapping data allowed the construction of a comparative map that confirms and expands the knowledge about evolutionary conservation and break points between the X chromosomes of the three mammalian species.

A radiation hybrid map of river buffalo (Bubalus bubalis) chromosome 1 (BBU1)

The largest chromosome in the river buffalo karyotype, BBU1, is a submetacentric chromosome with reported homology between BBU1q and bovine chromosome 1 and between BBU1p and BTA27. We present the first radiation hybrid map of this chromosome containing 69 cattle derived markers including 48 coding genes, 17 microsatellites and four ESTs distributed in two linkage groups spanning a total length of 1330.1 cR(5000). The RH map was constructed based on analysis of a recently developed river buffalo-hamster whole genome radiation hybrid (BBURH(5000)) panel. The retention frequency of individual markers across the panel ranged from 17.8 to 52.2%. With few exceptions, the order of markers within linkage groups is identical to the order established for corresponding cattle RH maps. The BBU1 map provides a starting point for comparison of gene order rearrangements between river buffalo chromosome 1 and its bovine homologs.