Sequence of the chicken sex chromosomes

In birds, as in mammals, the chromosome complement determines sex. Male birds are designated ZZ, female ZW. Mammals have the opposite system; males are XY and females XX. Both the avian ZW and mammalian XY pair are believed to have evolved from autosomes, with dramatic changes, both gene loss as well as gene acquisition and amplification occurring on the sex-specific W and Y chromosomes. In contrast, Z and X chromosomes are assumed to have diverged little from their autosomal progenitors. The Z and W sex chromosomes of the chicken provide a unique opportunity to study the evolution of sex chromosomes in a second lineage with an alternate system of heterogamety. We produced the finished sequence of the chicken Z chromosome and generated female-specific markers necessary to produce a complete sequence of the chicken W chromosome. Already our analysis of the Z chromosome has revealed that the sex chromosomes of birds evolved independently of the sex chromosomes of mammals. Despite this independence, the chicken Z chromosome converged on a suite of features analogous to those of the human X chromosome: low gene density, an enrichment for interspersed repeats, and large multi-copy gene families expressed in the testis. These features arose during the evolution of the Z and X chromosomes as sex chromosomes, overturning the notion that Z and X chromosomes are evolutionarily stable. Our preliminary efforts on the W chromosome have provided insights into its structure and underscore the ubiquity of gene acquisition and amplification on vertebrate sex chromosomes. As we accumulate genomic data from additional sex chromosomes, explaining the evolutionary forces that result in gene acquisition and amplification will remain a major challenge.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Bellott, Daniel Winston

Advisor dc:contributor.advisor

• David C. Page.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/57992

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/57992