EVOLUTION OF THE AVIAN SEX CHROMOSOMES FROM AN ANCESTRAL PAIR OF AUTOSOMES

Authors: FRIDOLFSSON, ANNA-KARIN - SWEDISH UNIV OF AG SCI; Cheng, Hans; COPELAND, NEAL - FREDERICK CANCER RSCH CTR; JENKINS, NANCY - FREDERICK CANCER RSCH CTR; LIU, HSIAO-CHING - FORMER ARS EMPLOYEE; RAUDSEPP, TERJE - SWEDISH UNIV OF AG SCI; WOODAGE, TREVOR - NIH BETHSEDA MD; CHOWDHARY, BHANU - SWEDISH UNIV OF AG SCI; HALVERSON, JOY - PE AG GEN DAVIS CA; ELLEGREN, HANS - SWEDISH UNIV OF AG SCI

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Among the mechanisms whereby sex is determined in animals, chromosomal sex determination is found in a wide variety of distant taxa. The widespread but not ubiquitous, not even within lineages, occurrence of chromosomal sex determination suggests that sex chromosomes have evolved independently several times during animal radiation. The most favored model for this process is gradual differentiation of ancestral pairs of autosomes. As known for mammals, sex chromosomes may have a very ancient origin and it has even been speculated that the sex chromosomes of mammals and birds would share a common chromosomal ancestry. In this study we show that the two genes, ATP5A1 and CHD1, so far assigned to the female-specific W chromosome of birds exist in a very closely related coy on the Z chromosome, but are not pseudoautosomal. This, together with other observations, indicates a common ancestry of the two sex chromosomes, consistent with the evolution from a pair of autosomes. However, comparative mapping demonstrates that the ATP5A1 and CHD1 genes are not sex-linked among eutherian mammals, this is also not the case for the majority of other genes so far assigned to the avian Z chromosome. We suggest that the evolution of sex chromosomes has occurred independently in mammals and birds.

Technical Abstract: With the development of a genetic map of the chicken, there are many uses and applications that were not possible previously. One example described in this paper is on the evolution of avian sex chromosomes. By comparing the same genes between the mouse and chicken genomes, it can be shown that the chicken sex chromosomes arose independently in both species, i.e., the sex chromosomes in mouse and chicken do not share a common origin. This knowledge is of fundamental interest for evolutionary biologists and also provides valuable data to scientists on identifying economically important genes in the chicken based on the location in the mouse genome.