1022-7954/03/3906- $25.00 © 2003 MAIK “Nauka /Interperiodica” 0681 Russian Journal of Genetics, Vol. 39, No. 6, 2003, pp. 681–686. Translated from Genetika, Vol. 39, No. 6, 2003, pp. 819–825. Original Russian Text Copyright © 2003 by Sazanov, Sazanova, Kozyreva, Smirnov, Andreozzi, Federico, Motta, Saccone, Bernardi. INTRODUCTION Compositional mapping consists in determining the distribution along chromosomes of extended (at least 300 kb) DNA fractions with homogeneous nucleotide composition, referred to as isochores [1]. Of particular interest is comparing the compositional and cytoge- netic chromosome maps and correlating isochore frac- tions with morphological (centromeres and telomeres) and cytochemical (G/R bands) markers. In most animal species, DNA fractions differing in the buoyant density are obtained by centrifugation of DNA fragments in sucrose gradient. This reflects DNA heterogeneity for the nucleotide composition: the GC- rich sequences have higher buoyant density than AT- rich ones. In human, two “light” (L1, c = 1.698 and L2, c = 1.700) and three “heavy” (H1, c = 1.704; H2, c = 1.708; and H3, c = 1.712) isochore families were found [1–5]. In the mouse genome, the families L1, L2, H1, and H2 are present [6]. The light isochores comprise about 63% of the mammalian genome [3]. In the cold- blooded animals, only the light isochore families, L1 and L2, are presented [4]. In several avian species belonging to different taxa, the genome composition was shown to be homoge- neous [6]. Unlike mammals, birds have a family of heavy isochores H4 (c = 1.712) [6]. In addition, heavy isochore fractions contain a GC-rich satellite character- istic of birds and reptiles [6]. In mammals, different isochore families are irregu- larly distributed. The heaviest H3 isochores were local- ized to T bands, where concentration of genes, espe- cially of housekeeping genes and oncogenes is the highest. In general, the light isochore fractions tend to be located in G bands, where gene concentration is much lower than in R bands and mostly tissue-specific genes are present, while heavy isochores are mainly associated with R bands [7, 8]. The avian karyotype has some morphological fea- tures that are interesting with respect to the composi- tional mapping. Microchromosomes constitute about 30% of the avian genome. They are not only much shorter than macrochromosomes, but also possess spe- cific cytological and biochemical features [9]. Micro- chromosomes are R-positive and GC-rich [10]. Unlike macrochromosomes, microchromosomes contain many Comparative Compositional Mapping of Chicken and Quail Chromosomes A. A. Sazanov 1 , A. L. Sazanova 2 , A. A. Kozyreva 2 , A. F. Smirnov 1, 2 , L. Andreozzi 3 , C. Federico 3 , S. Motta 3 , S. Saccone 3, 4 , and G. Bernardi 5 1 All-Russia Institute of Animal Genetics and Breeding, Russian Academy of Agricultural Sciences, St. Petersburg, Pushkin, 189504 Russia; fax: (812) 470-99-89; e-mail: Alexei_Sazanov@mail.ru 2 Biological Research Institute, St. Petersburg State University, St. Petersburg, Stary Petergof, 198504 Russia 3 Dipartamento di Biologia Animale, University of Catania, Catania, 95124 Italy; fax: (812) 428-77-33; e-mail: Anna_Sazanova@mail.ru, Aleksandr. Smirnov@paloma. spbu.ru 4 Dipartamento di Protezione e Valorizzazione Agroalimentare, Sez. Allevamenti Zootecnici, University of Bologna, Regio Emilia, Italy 5 Laboratorio di Evoluzione Molecolare, Stazione Zoologica Anton Dohrn, Villa Comunale, Napoli, 80121 Italy Received June 20, 2002 Abstract—The distribution of various isochore families on mitotic chromosomes of domestic chicken and Jap- anese quail was studied by the method of fluorescence in situ DNA–DNA hybridization (FISH). DNA of vari- ous isochore families was shown to be distributed irregularly and similarly on chromosomes of domestic chicken and Japanese quail. The GC-rich isochore families (H2, H3, and H4) hybridized mainly to microchro- mosomes and a majority of macrochromosome telomeric regions. In chicken, an intense fluorescence was also in a structural heterochromatin region of the Z chromosome long arm. In some regions of the quail macrochro- mosome arms, hybridization was also with isochore families H3 and H4. On macrochromosomes of both spe- cies, the pattern of hybridization with isochores of the H2 and H3 families resembled R-banding. The light iso- chores (L1 and L2 families) are mostly detected within macrochromosome internal regions corresponding to G bands, whereas microchromosomes lack light isochores. Although mammalian and avian karyotypes differ significantly in organization, the isochore distribution in genomes of these two lineages of the warm-blooded animals is similar in principle. On macrochromosomes of the two avian species studied, a pattern of isochore dis- tribution resembled that of mammalian chromosomes. The main specific feature of the avian genome, a great num- ber of microchromosomes (about 30% of the genome), determines a compositional specialization of the latter. This suggests the existence of not only structural but also functional compartmentalization of the avian genome. ANIMAL GENETICS