By Dr Ananya Mandal, MD
DNA carries the genetic information of species and has been evolving over millions of years. Earlier studies of prehistoric and historical migrations of human populations were possible only by research on uncovered skeletal remains and fossils.
Over the last two or three decades anthropologists have developed a more powerful tool in the form of molecular biology. In evolution, proteins and certain molecules have been analyzed over years and decades but it was in the 80’s that these were first done more precisely to be of use.
Researchers after that have gained a better understanding of the DNA sequences. Assessment of these sequences gives an insight into the population or between populations.
DNA is the only biomolecule that has been constantly changing over millions of years and yet maintains a basic pattern that carries a record of life’s evolution on Earth. Genes carry a variety of sequences, amongst them some carrying important information, e.g., functional genes which encode for the proteins that form the building blocks of the body as well as several regulatory fragments that determine DNA reading in formation of enzymes, proteins and hormones.
Is “junk DNA” really junk?
DNA contains a vast amount of non-coding and non-functional sequences. These remain switched off and contain mutated genes or those inserted from other organisms, e.g., viruses and bacteria.
Much of these DNA that were not coding for any proteins were termed “junk DNA”. Now, in a series of papers published in September in Nature (Scientific American is part of Nature Publishing Group) and elsewhere, the ENCODE group have found that there may be signals and switches present in this junk DNA. This has paved ways to discover human inheritance and disease over ages.
The majority of the DNA is located within the cell nucleus. Minute amounts of genetic material, however, are present in a separate cellular organelle – the mitochondrion. This is called mitochondrial DNA or mtDNA.
mtDNa is the most useful tool in analyzing the evolution of a species. Different different population histories are being reflected in mtDNA lineages and nuclear gene frequencies or language changes.
DNA in nuclei compared to mitochondrial DNA
Since there are different inheritance patterns of both forms of DNA material, it is significant to note that while DNA within the nucleus comes from both parents, that in the cell cytoplasm or in the mitochondria comes from the mother.
It is noted that over ages there is a difference in migration and mobility between men and women. It is not clear, however, which of the sexes moved more frequently. However, it is seen that the male sex chromosome or the Y chromosome sequences is more geographically structured than the mitochondrial DNA suggesting the males tended to stay in one place while females and families resided in husband’s abode.
Studies also suggest that these mtDNA changes may have resulted from higher male than female migration rate in the period of Mesolithic recolonisation when Northern Europe became inhabitable again after the Ice Age. This suggests that female migration, more than male, may affect the structure of nuclear genes.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)