Bird-brained molecular sexing

A recent study on the evolution of avian sex chromosomes has focused on retroposons as a novel method for reconstructing gametologous gene trees.

Alexander Suh and his team at the University of Münster looked at Z-/W-presence or Z-presence/W-absence regions among 126 sequenced intron pairs for all birds.1 The vast majority of extant birds possess highly differentiated Z and W sex chromosomes. All female birds (ZW) carry two distinct copies of these gametologues, while males (ZZ) have only one.

Suh found four regions in three gametologues: CHD1, NIPBL and ATP5A1. Their data confirmed that the CHD1Z/CHD1W genes differentiated in the ancestor of the neognaths. The NIPBLZ/NIPBLW genes diverged early in the neoavian ancestor and independently within Galloanserae. The divergence of the ATP5A1Z/ATP5A1W genes in galloanserans occurred independently and appears to have diverged fairly recently.

The practical application behind this study allows for three of the investigated loci to be utilized as independent tools for molecular sexing of Neoaves or Neognathae. When any of the four regions are copied a million-fold using a polymerase chain reaction (PCR), then separated by size using gel electrophoresis, the resulting PCR amplicons provide an explicit method for identifying the sex of birds. This depends upon the region that is amplified.

1. Alexander Suh et al., Molecular Biology and Evolution, 2011, doi: 10.1093/molbev/msr147

This story originally appeared in The Column. Click here to view that issue.