The Crest Phenotype in Chicken Is Associated with Ectopic Expression of HOXC8 in Cranial Skin

The Crest phenotype is characterised by a tuft of elongated feathers atop the head. A similar phenotype is also seen in several wild bird species. Crest shows an autosomal incompletely dominant mode of inheritance and is associated with cerebral hernia. Here we show, using linkage analysis and genome-wide association, that Crest is located on the E22C19W28 linkage group and that it shows complete association to the HOXC-cluster on this chromosome. Expression analysis of tissues from Crested and non-crested chickens, representing 26 different breeds, revealed that HOXC8, but not HOXC12 or HOXC13, showed ectopic expression in cranial skin during embryonic development. We propose that Crest is caused by a cis-acting regulatory mutation underlying the ectopic expression of HOXC8. However, the identification of the causative mutation(s) has to await until a method becomes available for assembling this chromosomal region. Crest is unfortunately located in a genomic region that has so far defied all attempts to establish a contiguous sequence

Duplication and divergence: the evolution of new genes and old ideas

Over 35 years ago, Susumu Ohno stated that gene duplication was the single most important factor in evolution (97). He reiterated this point a few years later in proposing that without duplicated genes the creation of metazoans, vertebrates, and mammals from unicellular organisms would have been impossible. Such big leaps in evolution, he argued, required the creation of new gene loci with previously nonexistent functions (98). Bold statements such as these, combined with his proposal that at least one whole-genome duplication event facilitated the evolution of vertebrates, have made Ohno an icon in the literature on genome evolution. However, discussion on the occurrence and consequences of gene and genome duplication events has a much longer, and often neglected, history. Here we review literature dealing with the occurence and consequences of gene duplication, begining in 1911. We document conceptual and technological advances in gene duplication research from this early research in comparative cytology up to recent research on whole genomes, "transcriptomes," and "interactomes."