Differences in gene density on chicken macrochromosomes and microchromosomes

The chicken karyotype comprises six pairs of large macrochromosomes and 33 pairs of smaller microchromosomes(1.) Cytogenetic evidence suggests that mi crochromosomes may be more gene-dense than macrochromosomes. In this paper, we compare the gene densities on macrochromosomes and microchromosomes bas ed on sequence sampling of cloned genomic DNA, and from the distribution of genes mapped by genetic linkage and physical mapping. From these different approaches we estimate that microchromosomes are twice as gene-dense as ma crochromosomes and show that sequence sampling is an effective means of gen e discovery in the chicken. Using this method we have also detected a conse rved linkage between the genes for serotonin 1D receptor (HTR1D) and the pl atelet-activating factor receptor protein gene (PTAFR) on chicken chromosom e 5 and human chromosome 1p34 .3. Taken together with its advantages as an experimental animal, and public access to genetic and physical mapping reso urces, the chicken is a useful model genome for studies on the structure, f unction and evolution of the vertebrate genome.