Identification of the sex-determining region in flathead grey mullet (Mugil cephalus).

Elucidation of the sex-determination mechanism in flathead grey mullet (Mugil cephalus) is required to exploit its economic potential by production of genetically determined monosex populations and application of hormonal treatment to parents rather than to the marketed progeny. Our objective was to construct a first-generation linkage map of the M. cephalus in order to identify the sex-determining region and sex-determination system. Deep-sequencing data of a single male was assembled and aligned to the genome of Nile tilapia (Oreochromis niloticus). A total 245 M. cephalus microsatellite markers were designed, spanning the syntenic tilapia genome assembly at intervals of 10 Mb. In the mapping family of full-sib progeny, 156 segregating markers were used to construct a first-generation linkage map of 24 linkage groups (LGs), corresponding to the number of chromosomes. The linkage map spanned approximately 1200 cM with an average inter-marker distance of 10.6 cM. Markers segregating on LG9 in two independent mapping families showed nearly complete concordance with gender (R2  = 0.95). The sex determining locus was fine mapped within an interval of 8.6 cM on LG9. The sex of offspring was determined only by the alleles transmitted from the father, thus indicating an XY sex-determination system.

Chimaerism detection in bovine twins, triplets and quadruplets using sex chromosome-linked markers.

The phenomenon of chimaerism occurs in the majority of cattle twin pregnancies. The objectives of this study were to develop a powerful diagnostic test for chimaerism in bovine male and female co-twins using X and Y chromosome-linked markers and to determine the extent of chimaerism in twins, triplets and quadruplets. We developed a multiplex PCR set of three polymorphic markers on chromosome X (DIK2865, DIK2283, AGLA257), where the presence of >1 and >2 alleles per marker is sufficient to prove chimaerism in males and females, respectively. In addition, a specific segment on chromosome Y (BOV97M) is included in the set to indicate chimaerism in females. Visualization of chimaeric alleles was best for DNA extracted from blood, fair for DNA from vaginal smears and failed for DNA extracted from hair. The power of chimaerism identification using this set of markers for DNA extracted from blood was calculated as 99% in males and virtually 100% in females. All females and males in heterosexual twins, triplets and quadruplets displayed evidence of a chimaeric allele in at least one and maximum of three of three X chromosome markers analysed. In addition, all females showed the presence of the BOV97M segment and were validated as chimaeric by the standard clinical diagnosis of impaired vaginal length. Quantitative PCR analysis of BOV97M copies in all twins vs. their sires showed a mean ratio of 45-68% in females and 39-49% in males, indicating a substantial symmetrical exchange of cells among all co-twins. The proposed analysis of X and Y chromosome-linked markers is advantageous to previous methods based on Y chromosome sequences only, because it detects chimaerism in both male and female co-twins.

An ordered comparative map of the cattle and human genomes.

A cattle-human whole-genome comparative map was constructed using parallel radiation hybrid (RH) mapping in conjunction with EST sequencing, database mining for unmapped cattle genes, and a predictive bioinformatics approach (COMPASS) for targeting specific homologous regions. A total of 768 genes were placed on the RH map in addition to 319 microsatellites used as anchor markers. Of these, 638 had human orthologs with mapping data, thus permitting construction of an ordered comparative map. The large number of ordered loci revealed > or =105 conserved segments between the two genomes. The comparative map suggests that 41 translocation events, a minimum of 54 internal rearrangements, and repositioning of all but one centromere can account for the observed organizations of the cattle and human genomes. In addition, the COMPASS in silico mapping tool was shown to be 95% accurate in its ability to predict cattle chromosome location from random sequence data, demonstrating this tool to be valuable for efficient targeting of specific regions for detailed mapping. The comparative map generated will be a cornerstone for elucidating mammalian chromosome phylogeny and the identification of genes of agricultural importance."Ought we, for instance, to begin by discussing each separate species-in virtue of some common element of their nature, and proceed from this as a basis for the consideration of them separately?" from Aristotle, On the Parts of Animals, 350 B.C.E.

Comparative organization of cattle chromosome 5 revealed by comparative mapping by annotation and sequence similarity and radiation hybrid mapping.

A whole genome cattle-hamster radiation hybrid cell panel was used to construct a map of 54 markers located on bovine chromosome 5 (BTA5). Of the 54 markers, 34 are microsatellites selected from the cattle linkage map and 20 are genes. Among the 20 mapped genes, 10 are new assignments that were made by using the comparative mapping by annotation and sequence similarity strategy. A LOD-3 radiation hybrid framework map consisting of 21 markers was constructed. The relatively low retention frequency of markers on this chromosome (19%) prevented unambiguous ordering of the other 33 markers. The length of the map is 398.7 cR, corresponding to a ratio of approximately 2.8 cR(5,000)/cM. Type I genes were binned for comparison of gene order among cattle, humans, and mice. Multiple internal rearrangements within conserved syntenic groups were apparent upon comparison of gene order on BTA5 and HSA12 and HSA22. A similarly high number of rearrangements were observed between BTA5 and MMU6, MMU10, and MMU15. The detailed comparative map of BTA5 should facilitate identification of genes affecting economically important traits that have been mapped to this chromosome and should contribute to our understanding of mammalian chromosome evolution.