It is widely recognised that dogs provide a fine example of one species (a domesticated wolf) whose different breeds exhibit very large variations in morphology. Some of these variants have a genetic origin, and the details of one of these traits (hairlessness) have recently been clarified.
"The American Kennel Club lists three breeds of hairless dogs: the Chinese crested; [. . .] the Mexican hairless dog; and the Peruvian Inca Orchid dog. These canines typically live a normal life span, though they lack the full set of 42 teeth common to other adult dogs. Researchers have long known that a dominant gene causes this set of abnormalities, called canine ectodermal dysplasia (CED). That means dogs need only inherit one copy of it to be bald; with this particular gene, two copies are lethal. But the gene itself remained a mystery."
Chinese crested dogs: hairless and coated. Graphic here (Tosso Leeb)
It is a mystery no longer, thanks to some detective work by a team of scientists led by Tosso Leeb, a veterinary geneticist at the University of Bern, Switzerland. According to one writeup, "Because Chinese crested dogs have been inbred for decades, the genomes of any two dogs are nearly identical, and slight variations are very apparent." So the researchers compared the genomes of hairless animals with those of "powderpuffs" - the same breed but with more normal hair.
"The technique, called genomewide association mapping, turned up a suspicious-looking region on chromosome 17. To investigate further, Leeb and his team collected additional DNA samples from a wider array of hairless and coated dogs. In all, they looked at 93 hairless and 49 coated Chinese crested dogs, 39 hairless and six coated Peruvian hairless dogs, and eight Mexican hairless dogs (there is no coated counterpart). Mapping the chromosome 17 sequences revealed an insertion of seven letters, or base pairs, of genetic code in a gene called FOXI3 in all of the hairless dogs. Although the exact function of the FOXI3 gene is unknown, other genes in the FOX family control embryonic development in mammals."
FOXI3 appears to function as a switch, with the mutation knocking out the normal development of parts of the unfortunate animal. "Leeb says the mutation most likely interferes with the genetic instructions for hair and teeth proteins, causing CED in dogs." There is particular interest because of the possible implications for humans:
"As it turns out, the human genome sequence that scientists use as a gold standard for deciphering genetic information contained a mistake in the FOXI3 gene, making it impossible for computer programs to find it. Another human sequence contains the correct information, confirming the existence of FOXI3 in people, as well as in mice and dogs, Leeb says."
Apparently, the team are currently engineering the FOXI3 mutation in mice, to find out more. The expectation is that the mutation will have comparable effects in mice, dogs and humans. One commentator suggested this could be a "starting point for research on new baldness remedies in humans".
So, the nature of this mutation is that it is a degeneration of the genome. There is no new information, but rather a loss leading to decreased functionality. These mutants are kept alive by mankind, whether they be Aztecs who considered them sacred nearly 4000 years ago, or whether they be proud owners who are prepared to pay $1000 for the experience of having one as a pet. Outside these environments, they would soon die. The take-home message is that these dogs are witnesses to the largely negative impact of mutations on living things. Darwinists have a hard task when they set out to convince the world that the rare occasional mutation is responsible for building complexity. We are rather short of any good examples of this.
This poor little rascal knows what it's like to have part of his genome deleted (Source here)
A Mutation in Hairless Dogs Implicates FOXI3 in Ectodermal Development
Cord Drogemuller, Elinor K. Karlsson, Marjo K. Hytonen, Michele Perloski, Gaudenz Dolf, Kirsi Sainio, Hannes Lohi, Kerstin Lindblad-Toh, and Tosso Leeb.
Science 321, 12 September 2008: 1462.
Abstract: Mexican and Peruvian hairless dogs and Chinese crested dogs are characterized by missing hair and teeth, a phenotype termed canine ectodermal dysplasia (CED). CED is inherited as a monogenic autosomal semidominant trait. With genomewide association analysis we mapped the CED mutation to a 102-kilo-base pair interval on chromosome 17. The associated interval contains a previously uncharacterized member of the forkhead box transcription factor family (FOXI3), which is specifically expressed in developing hair and teeth. Mutation analysis revealed a frameshift mutation within the FOXI3 coding sequence in hairless dogs. Thus, we have identified FOXI3 as a regulator of ectodermal development.
Callaway, E., When being bald and ugly is the lesser of two evils, (New Scientist, 11 September 2008)
Saey, T.H. A 'foxi' gene for dog baldness, (Science News: Thursday, September 11th, 2008)
Zelkowitz, R. How Much Is That Baldie in the Window? (ScienceNOW Daily News, 11 September 2008)
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