A new look at the evolution of avian sex chromosomes

@article{Stiglec2007ANL,
  title={A new look at the evolution of avian sex chromosomes},
  author={Rami Stiglec and Tariq Ezaz and Jennifer A. Marshall Graves},
  journal={Cytogenetic and Genome Research},
  year={2007},
  volume={117},
  pages={103 - 109}
}
Birds have a ubiquitous, female heterogametic, ZW sex chromosome system. The current model suggests that the Z chromosome and its degraded partner, the W chromosome, evolved from an ancestral pair of autosomes independently from the mammalian XY male heteromorphic sex chromosomes – which are similar in size, but not gene content (Graves, 1995; Fridolfsson et al., 1998). Furthermore the degradation of the W has been proposed to be progressive, with the basal clade of birds (the ratites… 

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