| Comparative mapping has been performed between the chicken and human genomes in regions corresponding to human chromosomes 1, 4, and 9, along with several other smaller areas of conserved synteny. These regions were initially chosen because of their relevance to previously identified Marek's disease (MD) resistance quantitative trait loci (QTL) (Vallejo et al. 1998, Yonash et al. 1999). Segments of chicken orthologues of mapped human genes were PCR-amplified from parental DNA of the East Lansing Backcross (BC) reference population, and the two parental alleles were sequenced. Single nucleotide polymorphisms (SNP) differences were then used to design allele-specific PCR primers with which to genotype the mapping panel; 52 BC progeny. Inheritance data were analyzed and the map location of the chicken orthologues were determined. Statistical analysis, based on the theoretical treatment of Nadeau and Taylor (1984), was performed using the region specific comparative map data to derive an estimate of the genome-wide conservation of gene order between avian (chicken) and mammalian (human) genomes. The average length of a conserved segment was calculated to be 38 ± 9 centimorgans (cM), approximately 1% of the present estimate of the total genome. This corresponds to a rate of .13 ± 0.04 reciprocal translocations per million years of evolution, a rate substantially less than found for some intra-mammalian genomes, suggesting an unusual level of evolutionary stability exists among avian genomes. A significant portion of human chromosome 9 was shown to correspond to a portion of the chicken Z sex chromosome, thereby providing some insight into the evolution of ZW-type chromosomal sex determination in birds.; In addition to the comparative map, the initial steps to building a physical map of the chicken genome were begun. Recently, through collaboration with the Texas A&M BAC Center, a 5-fold BAC library of the chicken genome has been generated. This is comprised of approximately 38,000 clones with an average insert size of 150 kb. The BAC library is composed of chromosomal DNA from a Jungle Fowl (JF) female parent of the reference population. Because of the relative marker density, MD QTL, and number and positions of conserved markers between humans and chickens, microchromsome E41 was chosen to begin the physical mapping project. The BAC library has been spotted on 20 nylon membrane filters and these were screened using radio-labeled probes derived from six markers on E41. Ten positive BAC clones have been identified from four of the six markers tested. |
