Birds are characterised by feathers, flight, a small genome and a very distinctive karyotype. Despite the large numbers of chromosomes, the diploid count of 2n ≈ 80 has remained remarkably constant with 63% of birds where 2n = 74–86, 24% with 2n = 66–74 and extremes of 2n = 40 and 2n = 142. Of these, the most studied is the chicken (2n = 78), and molecular cytogenetic probes generated from this species have been used to further understand the evolution of the avian genome. The ancestral karyotype is, it appears, very similar to that of the chicken, with chicken chromosomes 1, 2, 3, 4q, 5, 6, 7, 8, 9, 4p and Z representing the ancestral avian chromosomes 1–10 + Z; chromosome 4 being the most ancient. Avian evolution occurred primarily in three stages: the divergence of the group represented by extant ratites (emu, ostrich etc.) from the rest; divergence of the Galloanserae (chicken, turkey, duck, goose etc.) – the most studied group; and divergence of the ‘land’ and ‘water’ higher birds. Other than sex chromosome differentiation in the first divergence there are no specific changes associated with any of these evolutionary milestones although certain families and orders have undergone multiple fusions (and some fissions), which has reduced their chromosome number; the Falconiformes are the best described. Most changes, overall, seem to involve chromosomes 1, 2, 4, 10 and Z where the Z changes are intrachromosomal; there are also some recurring (convergent) events. Of these, the most puzzling involves chromosomes 4 and 10, which appear to have undergone multiple fissions and/or fusions throughout evolution – three possible hypotheses are presented to explain the findings. We conclude by speculating as to the reasons for the strange behaviour of these chromosomes as well as the role of telomeres and nuclear organisation in avian evolution.

Arnold AP: Sex chromosomes and brain gender. Nat Rev Neurosci 5:701–708 (2004).
Bed’Hom B, Coullin P, Guillier-Gencik Z, Moulin S, Bernheim A, Volobouev V: Characterization of the atypical karyotype of the black-winged kite Elanus caeruleus (Falconiformes: Accipitridae) by means of classical and molecular cytogenetic techniques. Chromosome Res 11:335–343 (2003).
Burt DW, Bruley C, Dunn IC, Jones CT, Ramage A, et al: The dynamics of chromosome evolution in birds and mammals. Nature 402:411–413 (1999).
Chowdhary BP, Raudsepp T: HSA4 and GGA4: remarkable conservation despite 300-Myr divergence. Genomics 64:102–105 (2000).
Christidis L: Animal Cytogenetics 4: Chordata 3 B: Aves (Gebrüder Borntraeger, Berlin 1990).
de Oliveira EH, Habermann FA, Lacerda O, Sbalqueiro IJ, Wienberg J, Muller S: Chromosome reshuffling in birds of prey: the karyotype of the world’s largest eagle (Harpy eagle, Harpia harpyja) compared to that of the chicken (Gallus gallus). Chromosoma 114:338–343 (2005).
Delany ME: Patterns of ribosomal gene variation in elite commercial chicken pure line populations. Anim Genet 31:110–116 (2000).
Denjean B, Ducos A, Darre A, Pinton A, Seguela A, et al: Caryotype des canards commun (Anas platyrhynchos), Barbarie (Cairina moschata) et de leur hybride. Revue Med Vet 148:695–704 (1997).
Derjusheva S, Kurganova A, Habermann F, Gaginskaya E: High chromosome conservation detected by comparative chromosome painting in chicken, pigeon and passerine birds. Chromosome Res 12:715–723 (2004).
Dimcheff DE, Drovetski SV, Mindell DP: Phylogeny of Tetraoninae and other galliform birds using mitochondrial 12S and ND2 genes. Mol Phylogenet Evol 24:203–215 (2002).
Donne-Gousse C, Laudet V, Hanni C: A molecular phylogeny of anseriformes based on mitochondrial DNA analysis. Mol Phylogenet Evol 23:339–356 (2002).
Edwards SV, Bryan Jennings W, Shedlock AM: Phylogenetics of modern birds in the era of genomics. Proc Biol Sci 272:979–992 (2005).
Foster HA, Bridger JM: The genome and the nucleus: a marriage made by evolution. Genome organisation and nuclear architecture. Chromosoma 114:212–229 (2005).
Galkina SA, Deryusheva S, Fillon V, Vignal A, Crooijmans R, et al: FISH on avian lampbrush chromosomes produces higher resolution gene mapping. Genetica 128:241–251 (2006).
Griffin DK, Haberman F, Masabanda J, O’Brien P, Bagga M, et al: Micro- and macrochromosome paints generated by flow cytometry and microdissection: tools for mapping the chicken genome. Cytogenet Cell Genet 87:278–281 (1999).
Guttenbach M, Nanda I, Feichtinger W, Masabanda JS, Griffin DK, Schmid M: Comparative chromosome painting of chicken autosomal paints 1–9 in nine different bird species. Cytogenet Genome Res 103:173–184 (2003).
Habermann FA, Cremer M, Walter J, Kreth G, von Hase J, et al: Arrangements of macro- and microchromosomes in chicken cells. Chromosome Res 9:569–584 (2001).
Hedges SB, Poling LL: A molecular phylogeny of reptiles. Science 283:998–1001 (1999).
Hughes AL, Piontkivska H: DNA repeat arrays in chicken and human genomes and the adaptive evolution of avian genome size. BMC Evol Biol 5:12 (2005).
ICGSC (International Chicken Genome Sequencing Consortium): Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution. Nature 432:695–716 (2004).
Itoh Y, Arnold AP: Chromosomal polymorphism and comparative painting analysis in the zebra finch. Chromosome Res 13:47–56 (2005).
Jaszczak K, Zawadzka M, Jaszczak J, Rabsztyn A: Karyotype vs DNA fingerprinting in geese. Anim Sci Papers Reports 20:103–109 (2002).
Kasai F, Garcia C, Arruga MV, Ferguson-Smith MA: Chromosome homology between chicken (Gallus gallus domesticus) and the red-legged partridge (Alectoris rufa); evidence of the occurrence of a neocentromere during evolution. Cytogenet Genome Res 102:326–330 (2003).
Kohn M, Hogel J, Vogel W, Minich P, Kehrer-Sawatzki H, et al: Reconstruction of a 450-My-old ancestral vertebrate protokaryotype. Trends Genet 22:203–210 (2006).
Kumar S, Hedges SB: A molecular timescale for vertebrate evolution. Nature 392:917–920 (1998).
Kumazawa Y, Nishida M: Complete mitochondrial DNA sequences of the green turtle and blue-tailed mole skink: statistical evidence for archosaurian affinity of turtles. Mol Biol Evol 16:784–792 (1999).
Ladjali-Mohammedi K, Bitgood JJ, Tixier-Boi- chard M, Ponce De Leon FA: International system for standardized avian karyotypes (ISSAK): standardized banded karyotypes of the domestic fowl (Gallus domesticus). Cytogenet Cell Genet 86:271–276 (1999).
Marshall Graves JA, Shetty S: Sex from W to Z: evolution of vertebrate sex chromosomes and sex determining genes. J Exp Zool 290:449–462 (2001).
Masabanda JS, Burt DW, O’Brien PC, Vignal A, Fillon V, et al: Molecular cytogenetic definition of the chicken genome: the first complete avian karyotype. Genetics 166:1367–1373 (2004).
Matsuda Y, Nishida-Umehara C, Tarui H, Kuroiwa A, Yamada K, et al: Highly conserved linkage homology between birds and turtles: bird and turtle chromosomes are precise counterparts of each other. Chromosome Res 13:601–615 (2005).
Meyne J, Ratliff RL, Moyzis RK: Conservation of the human telomere sequence (TTAGGG)n among vertebrates. Proc Natl Acad Sci USA 86:7049–7053 (1989).
Meyne J, Baker RJ, Hobart HH, Hsu TC, Ryder OA, et al: Distribution of non-telomeric sites of the (TTAGGG)n telomeric sequence in vertebrate chromosomes. Chromosoma 99:3–10 (1990).
Muller J, Reisz RR: Four well-constrained calibration points from the vertebrate fossil record for molecular clock estimates. Bioessays 27:1069–1075 (2005).
Nanda I, Schmid M: Localization of the telomeric (TTAGGG)n sequence in chicken (Gallus domesticus) chromosomes. Cytogenet Cell Genet 65:190–193 (1994).
Nanda I, Schrama D, Feichtinger W, Haaf T, Schartl M, Schmid M: Distribution of telomeric (TTAGGG)(n) sequences in avian chromosomes. Chromosoma 111:215–227 (2002).
Nanda I, Karl E, Volobouev V, Griffin DK, Schartl M, Schmid M: Extensive gross genomic rearrangements between chicken and Old World vultures (Falconiformes: Accipitridae). Cytogenet Genome Res 112:286–295 (2006).
Raudsepp T, Houck ML, O’Brien PC, Ferguson-Smith MA, Ryder OA, Chowdhary BP: Cytogenetic analysis of California condor (Gymnogyps californianus) chromosomes: comparison with chicken (Gallus gallus) macrochromosomes. Cytogenet Genome Res 98:54–60 (2002).
Rodionov AV: Evolution of avian chromosomes and linkage groups. Russ J Genet 33:605–617 (1997).
Schmid M, Nanda I, Guttenbach M, Steinlein C, Hoehn M, et al: First report on chicken genes and chromosomes 2000. Cytogenet Cell Genet 90:169–218 (2000).
Schmid M, Nanda I, Hoehn H, Schartl M, Haaf T, et al: Second report on chicken genes and chromosomes 2005. Cytogenet Genome Res 109:415–479 (2005).
Shetty S, Griffin DK, Graves JA: Comparative painting reveals strong chromosome homology over 80 million years of bird evolution. Chromosome Res 7:289–295 (1999).
Shibusawa M, Minai S, Nishida-Umehara C, Suzuki T, Mano T, et al: A comparative cytogenetic study of chromosome homology between chicken and Japanese quail. Cytogenet Cell Genet 95:103–109 (2001).
Shibusawa M, Nishida-Umehara C, Masabanda J, Griffin DK, Isobe T, Matsuda Y: Chromosome rearrangements between chicken and guinea fowl defined by comparative chromosome painting and FISH mapping of DNA clones. Cytogenet Genome Res 98:225–230 (2002).
Shibusawa M, Nishibori M, Nishida-Umehara C, Tsudzuki M, Masabanda J, et al: Karyotypic evolution in the Galliformes: an examination of the process of karyotypic evolution by comparison of the molecular cytogenetic findings with the molecular phylogeny. Cytogenet Genome Res 106:111–119 (2004a).
Shibusawa M, Nishida-Umehara C, Tsudzuki M, Masabanda J, Griffin DK, Matsuda Y: A comparative karyological study of the blue-breasted quail (Coturnix chinensis, Phasianidae) and California quail (Callipepla californica, Odontophoridae). Cytogenet Genome Res 106:82–90 (2004b).
Shields GF: Comparative Avian cytogenetics: A review. Condor 84:45–58 (1982).
Stock AD, Bunch TD: The evolutionary implications of chromosome banding pattern homologies in the bird order Galliformes. Cytogenet Cell Genet 34:136–148 (1982).
Stock AD, Mengden GA: Chromosome banding pattern conservatism in birds and nonhomology of chromosome banding patterns between birds, turtles, snakes and amphibians. Chromosoma 50:69–77 (1975).
Summers AP: Evolution: warm-hearted crocs. Nature 434:833–834 (2005).
Takagi N, Sasaki M: A phylogenetic study of bird karyotypes. Chromosoma 46:91–120 (1974).
van Tuinen M, Hedges SB: Calibration of avian molecular clocks. Mol Biol Evol 18:206–213 (2001).
van Tuinen M, Sibley CG, Hedges SB: The early history of modern birds inferred from DNA sequences of nuclear and mitochondrial ribosomal genes. Mol Biol Evol 17:451–457 (2000).
Wienberg J: The evolution of eutherian chromosomes. Curr Opin Genet Dev 14:657–66 (2004).
Yang F, Muller S, Just R, Ferguson-Smith MA, Wienberg J: Comparative chromosome painting in mammals: human and the Indian muntjac (Muntiacus muntjak vaginalis). Genomics 39:396–401 (1997).
Zardoya R, Meyer A: The evolutionary position of turtles revised. Naturwissenschaften 88:193–200 (2001).
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.