Chromosome chain makes a link

摘要

The platypus' sex chromosomes are as peculiar as its appearance. Five X and five Y chromosomes form a remarkable chain-like configuration in male reproductive cells that ensures appropriate sperm formation. An Australian Aboriginal legend proposes that the platypus is the offspring of a duck and a water-rat, with a duck-like bill and webbed toes, but four feet and fur like a rat. However, despite some avian and reptilian features, phylo-genetic studies classify the platypus as a monotreme, an egg-laying mammal. Mono-tremes diverged from the rest of the mammalian lineage some 210 million years ago, and examining them not only gives a unique evolutionary perspective to biological processes specific to mammals, but also provides links to more distant animals, such as birds.