Monday, 8 April 2013

The Equine 'Adam' Lived Fairly Recently: Close Relationships Among Modern Stallions

Apr. 4, 2013 — The analysis of DNA inherited from a single parent has provided valuable insights into the history of human and animal populations. However, until recently we had insufficient information to be able to investigate the paternal lines of the domestic horse. This gap has been filled by Barbara Wallner and colleagues at the University of Veterinary Medicine, Vienna, who present information on the genetic variability in the horse Y chromosome and show how various breeds of the modern horse are interrelated.

The results have just been published in the online journal PLOS ONE.

Pedigree of Darley Arabians progeny depicting the origin of HT3 from HT2. Breeds of analysed males are listed on the bottom and the haplotypes of their ancestors are reconstructed (HT2-yellow, HT3-red, unknown-grey). Selected famous stallions are shown by name; dotted lines connect relatives where at least one ancestor is omitted. No descendants from “Pot8os” and “Waxy” were available apart from “Whalebone, 1807”. The mutation leading to HT3 must have occurred either in the germline of stallion “Eclipse” [54] or in his son “Pot8os” or in his grandson “Waxy” and rose to very high frequency in the English Thoroughbred and many sport horse breeds through the progeny of the stallion “Whalebone”. (Credit: Barbara Wallner et al. Identification of Genetic Variation on the Horse Y Chromosome and the Tracing of Male Founder Lineages in Modern Breeds. PLoS ONE, 2013; 8 (4): e60015 DOI: 10.1371/journal.pone.0060015)

In mammals, an individual's sex is determined by the chromosomes it inherits from its parents. Two X chromosomes lead to a female, whereas one X and one Y lead to a male. Y chromosomes are only passed from fathers to sons, so each Y chromosome represents the male genealogy of the animal in question. In contrast, mitochondria are passed on by mothers to all their offspring. This means that an analysis of the genetic material or DNA of mitochondria can give information on the female ancestry. For the modern horse, it is well known that mitochondrial DNA is extremely diverse and this has been interpreted to mean that many ancestral female horses have passed their DNA on to modern horse breeds. Until recently, though, essentially no sequence diversity had been detected on the Y chromosome of the domestic horse. Not only does the lack of sequence markers on the Y chromosome make it impossible to trace male lineages with confidence, it also represents a scientific paradox. How can a species with so many female lines have so few male lines? The issue has now been addressed by Barbara Wallner and colleagues at the Institute of Animal Breeding and Genetics, University of Veterinary Medicine, Vienna (Vetmeduni Vienna).

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