Genetic mechanisms involved in the periodicity of flight

Abstract

Abstract The periodicity of the chemical elements is a well established phenomenon which took over 100 years to elucidate. Although there are exceptions, most phenomena in chemistry are at present explained on the basis of this periodicity. One of the relevant features of the Periodic Table is that the simplest as well as the most complex elements may have the same basic properties. The introduction of the concept of periodicity in biology, may seem as inappropriate to biologists as it was to chemists in the last century. However, the advancement of molecular biology allows to consider most of the structures and functions that have arisen in biological evolution as periodic events. In the present article flight is described, as one example of biological periodicity. Although the invertebrates comprise 30 phyla, flight arose only in the Arthropoda, and within this group only in the insects. The second time flight appeared is in the pterosaurs (flying reptiles) which were not directly related to the insects. The third event took place when the birds emerged which had as ancestors flightless reptiles, such as the Thecodonts. Among the mammals appeared the bats, with their impressive flying capacity, and without any direct relationship to the birds. The teleosts only emerged about 190 million years ago. Among them a few species fly and do it in an environment adverse to their respiration, namely in air. The periodicity of flight is characterized by the imposition of the same basic solution independently of the organism's biological complexity. The genetics of the periodicity of flight can now be understood on the basis of the molecular organization of homeotic genes. These DNA sequences are responsible for the production of the body segments in insects, birds and mammals. The wing of a bird and that of an insect, which before were considered to be unrelated, turn out to be determined by the same type of homeotic genes. Moreover, these genes have been highly conserved from yeast to humans. The molecular analysis of the homeotic genes in Drosophila has allowed to produce four-winged flies. The new wings emerge as “ready made” structures, the pattern being fully coherent from the onset. The position of the wings is not accidental and is the result of ordered chromosome rearrangements that involve transposons. The chromosome transformation apparently reenacts in days, what has occurred millions of years ago in other insects, that have four wings, such as the butterflies. Hence, the wings both in insects and birds, may have emerged not as the result of a need or of an advantage, but as “a surprise” to the animal, dictated by the molecular evolution of DNA. The evidence available at present allows to enunciate a general rule of biological periodicity: “The structures and functions of living organisms appear as a periodic function of the amount of their DNA and the configuration of its base sequences”. The six atoms present in DNA, RNA and the polypeptides of proteins: H, O, C, N, P and S are all non-metals and occupy a “niche” in the Periodic Table. Predictions based on the occurrence of biological periodicity may lead to fill some of the “black boxes” found in organism evolution. Among other results it is expected that humans, with their own wings, will be obtained when the DNA sequences, responsible for the wings of bats, will be isolated and introduced into fertilized human eggs.