title: Distribution of telomeric (TTAGGG)(n) sequences in avian chromosomes.
abstract: The physical ends of mammalian and other vertebrate chromosomes consist of tandemly repeated (TTAGGG)(n) hexamers, nucleating a specialized telomeric structure. However, (TTAGGG)(n) sequences can also occur at non-telomeric sites, providing important insights into karyotypic evolution. By fluorescence in situ hybridization (FISH) we studied the chromosomal distribution of (TTAGGG)(n) sequences in 16 bird species, representing seven different orders. Many species, in particular the ratites, display (TTAGGG)(n) hybridization signals in interstitial and centromeric regions of their macrochromosomes in addition to the typical telomeric signals. In some but not all species these non-telomeric sites coincide with C-band-positive heterochromatin. The retention and/or amplification of telomeric (TTAGGG)(n) repeats at interstitial and centromeric sites may indicate the fusion of ancestral chromosomes. Compared with the macrochromosomes, the microchromosomes of most species are enriched with (TTAGGG)(n) sequences, displaying heterogeneous hybridization patterns. We propose that this high density of (TTAGGG)(n) repeats contributes to the exceptionally high meiotic recombination rate of avian microchromosomes.
authors.affiliation: Department of Human Genetics, University of Würzburg, Würzburg, Germany.
authors.forename: Indrajit
authors.initials: I
authors.lastname: Nanda
authors.forename: David
authors.initials: D
authors.lastname: Schrama
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Feichtinger
authors.forename: Thomas
authors.initials: T
authors.lastname: Haaf
authors.forename: Manfred
authors.initials: M
authors.lastname: Schartl
authors.forename: Michael
authors.initials: M
authors.lastname: Schmid
mesh_terms: D000818:Animals; D001717:Birds / Q000145:classification / Q000235:genetics*; D018929:Cell Culture Techniques; D002503:Centromere; D016678:Genome; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D016615:Telomere / Q000737:chemistry / Q000235:genetics*