All chromosomes great and small: 10 years on

Abstract

There are no two ways about it; the avian karyotype is unique. To someone who looks at cytogenetic preparations of birds a lot (and we do), an avian chromosome preparation is nearly as characteristic as a feather when identifying a member of the phylogenetic class Aves. It is not just the microchromosomes, and many animal groups have microchromosomes (lizards, turtles, snakes, etc., may have ~20 microchromosome pairs), it is the fact that there are so many of them (~30), and they are so small (often described as “dot shaped”) that set birds apart. It is somewhat difficult to keep count, but as far as we are aware, there are 1,000+ published avian karyotypes. The most comprehensive overview to date was the classic work of Christidis (1990) with 800 species, and there have been a few hundreds more since then. Almost without exception, however, all these studies have one thing in common: they are woefully incomplete. Most stop at somewhere between the first 5 and 10 pairs, identify the se