Dog breed secrets revealed, as described in ScienceNOW, 14 Dec 2004. The distinctive features of some dog breeds have been found to be due to alterations in tandem repeats – regions of DNA where the same sequence is repeated many times. When these regions are being copied the machinery that does the copying can sometime lose track of where it is up to and leave out some of the repeated sequences or add in a few extra copies. Harold Garner and John Fondon of the University of Texas Southwestern Medical Centre analysed repetitive regions of DNA from 17 genes that are involved in growth and development in 92 different dog breeds. They then correlated the results with differences in bone structure of the different dog breeds. They found that snout length, a distinctive feature of many dogs, correlated with variations in repeat numbers in a gene named Runx-2. Wolves had less variation in repeats than domesticated dogs.

Editorial Comment: Dogs are a good example of variation within kind, and good evidence that genetic variation does not result in the evolution of new kinds. All the variation seen in domestic dogs has not made them evolve into any other kind of animal. Indeed, this study reminds us that most domestic dog breeds are the result of degeneration i.e. loss of genetic controls over certain gene segments followed by genetic mutations and copying errors in those segments. The degenerate dogs which result, only survive because human beings look after them. This is confirmed by the results in wolves. They have survived without human protection, so any degenerate mutations and copying errors have not survived to the next generation, i.e. natural selection keeps them multiplying after their kind and eliminates variation, so evolution cannot occur. (Ref. canines, degeneration, selection)


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