Indian Journal of Human Genetics
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Year : 1995  |  Volume : 1  |  Issue : 1  |  Page : 1-5

Lessons To Be Learned From Atavistic Mutations

Correspondence Address:
Susumu Ohno

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Source of Support: None, Conflict of Interest: None

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As a result of tetraplodization events in their past, the carp and the goldfish of the teleost order cypriniformes, as well as trouts and salmons of the order salmoniformes created redundancy at every locus. From the extinct rate of these redundant genes, the half-life of genes that became nonessential has been estimated in the range between 350 to 150 million years. The prediction that the trace of teraploid evolution can also be found in the mammalian genome appears to have been fulfilled. For example, in both man and the mouse, a set of genes encoding keratins, homeobox proteins and type I collagen a-chain is found not on one chromosome but on two nonhomologous chromosomes, as the original and its duplicate, thus indicating the conservation of paralogous segments since the teraploidization event that took place in our crossopterygian ancestor some 350 million years ago. It thus appears that genes more often than not remain immortal even after they become redundant, therefore, nonessential. This immortality also explains frequent recurrence of atavistic mutations: e.g., sperm whales re-growing a pair of hind legs 2.5 meters long and the horse of the order Perisodactyla sporting a pair of horns. It would be recalled that Michelangelo invariably adorned the head of Moses with a pair of horns.

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