Ed Young recently reopened the case of jumping genes in mammals. This article is a retake on an older piece originally published in 2013 in a different paper. Jumping genes or transposons are DNA sequences that can change position within a genome, sometimes creating or reversing mutations and altering the cell’s genetic identity and genome size. Some carry additional functions like antibiotic resistance in bacteria. In humans, the Alu sequence is about 300 bases long, is duplicated up to one million times representing up to 17% of the human genome, and is responsible for regulation of tissue-specific genes.
The long-held theory is that mammals obtain genes vertically while bacteria receive their genes vertically and also horizontally. But now it seems transposons can leave the DNA of one eukaryote species and enter that of another. For instance, a quarter of a cow’s DNA consists of one particular jumping gene, known as BovB. “If you compare different versions of the same gene across a range of animals … it’s like a window into a bizarre parallel universe where sheep are more closely related to cobras than they are to elephants, where kangaroos have more in common with bedbugs than with horses, and where pythons, zebrafish, leeches, scorpions, and sea urchins all belong to the same tight-knit family.” In addition, L1 (human Alu sequence) also “seems to have jumped between major animal groups”.
In conclusion, if DNA transfers so easily between high order organisms and between these and bacteria, then the value of DNA as a marker of inheritance diminishes to the point where it becomes unusable. In consequence, claims about the historical link between organisms that are based on DNA similarities revert to simple speculations.
Links:
http://phenomena.nationalgeographic.com/2013/01/01/how-a-quarter-of-the-cow-genome-came-from-snakes/