Genomic Changes And Adaptation

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Darwin proposed that species adapt to their environment through long periods of time, relative to a human’s life span, and with enough time would explain the diversity of organisms in the world. This adaption to the environment is what has allowed life to survive and spread across the world. However, although scientists today acknowledge this phenomenon, the mechanisms underlying environmental adaptation is still relatively new and unknown. In order to understand this mechanism for adaption, a 57 years long experiment was held. A Drosophila melanogaster (fruit fly) line was breed for 1400 generations under a condition of no light. The analysis of the genome of the flies in this experiment shows that the flies breed in darkness developed an adaptation that exhibits higher fecundity in dark than in light conditions. This means that the flies born from the generations of flies breed in darkness had an advantage when breeding in the dark, an adaptation to the darkness developed, and scientists have traced the adaptation to the mutation of genes encoding an olfactory receptor and a light receptor.

In the study of 1400 generations of flies, changes in the genome were found with the comparison of the experimental flies and the control strain. Approximately 220,000 single nucleotide polymorphisms (SNPs) and 4,700 insertions and deletions (InDels) were identified. Although these numbers appears to be incredibly large most of the changes in the genome were synonymous SNPs. Even with these alterations in the genome, the amino acids and proteins that were coded were unchanged. Only 1.8% of the identified SNPs were classified as non-synonymous (nsSNPs). These nsSNPs altered the amino acid sequence of gene product. An alteration of the amino acid sequence has the potential of altering protein structure and function leading to the formation of new proteins. The small cumulative nsSNPs leads to small phenotypic expressions different from the control group. These gene alterations present a case for the evolution of a species through adaptation with the cause of selective pressure.

The environmental selective pressure present in the experiment was an environment of darkness. For the flies this means that if they wanted to be the fittest, the best at producing fertile offspring, they needed to be able to effectively reproduce in the darkness. This pressure would cause the population of flies to favor specific flies. These flies would pass on their genetic information. Mutation would occur over many generations, and in this case 1400, and the mutations that provided an advantage for the selective pressure would be conserved while mutations that provided no benefits  or rendered the species less fit would disappear from the gene pool.

The mutations in the genome found that there were changes in genes that encode for olfactory receptors and light receptors. From this data we are able to conclude that in order to adapt to the selective pressure or darkness, the flies developed adaptations related to scent and light. Mutations found in the olfactory receptor genes are known to evolve in non-neutral manner and may be explained by the fact that these mutations would generate greater odor discrimination between individuals. Such adaptation would allow for greater ability to distinguish the surroundings of the fly and essentially this adaptation could and most probable resulted in a positive selection of the mutated genes.

What this experiment has observed is a population of fruit flies adapting to the selective pressure of darkness. Their adaptation resulted in a change in their ability to distinguish odors and light over 1400 generations. These phonotypical adaptations are then traced to specific genes that encodes for the sensing receptors. With these results it is possible to make a preliminary judgment that adaptation stems at a genetic level. Mutations occur in the genome of species and favorable mutations will be pasted through the generations resulting in observable variations. Diversity is a slow process that works at the genetic level but with time great changes can occur.


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