Absolute Truth

  

What caught my attention in the material for this week was really the article "The Identity Dance" by Gunjan Sinha. Coincidentally, I studied two other articles, for different classes, about gene, environment and phenotype. The first article was "Finding New Laws" by Dr. Pawan Kumar Dhar and it was published at Nature Magazine, (http://www.nature.com/nindia/2011/110309/full/nindia.2011.35.html). In this article,  Dr. Dhar explores the Mendelian Laws in the light of the great variation of phenotypes observed in nature for the same genotype. He concludes then that new laws are necessary to be created because the Mendelian Laws were based on elementary mathematics. Mendel artificially excluded the noise in his samples in order to create a pattern or a constant. However, if all variables that can influence the phenotype are added - which includes the environment- then, the result is more complex and could be better identified under statistical laws. 

            The second article, titled " A Higher Mutational Burden in Females Supports a ‘Female Protective Model’ in Neurodevelopmental Disorders" (http://download.cell.com/AJHG/pdf/PIIS0002929714000597.pdf?intermediate=true ) explored the direct relationship between gene and neurodevelopmental disorders (ND). It covered the association with deleterious CNV (copy number variants) and SNV (single nucleotide variant) as the cause of NDs. The authors concluded that females have more deleterious CNVs and SNVs than males which supports the theory that females have a protective model against NDs - the idea is that females need more mutations than males to express the disorder.

            Those three articles are basically tackling the same subject: the relationship among gene, environment and phenotype (the expression of certain characteristic) -by the way, identical twins are not genetically identical. Due to copy number variants, which are mutations, twins differ quite a bit. Mutations can happen during mitosis or meiosis, so even though twins could be genetically identical when they were born, while they grow up (mitosis) mutations happen.

            It is said that the phenotype is the result of the interaction between genotype and environment, but what is the weight of each one in the phenotype, it seems to be unknown. For example, one could argue that identical twins have different behavior because they had different life experiences and therefore it trigged different genes to express the behavior. Likewise, someone could say identical twins are different due to copy number variations, and therefore express different behaviors even if they seem to go through the same life experiences.

            I think the debate Nature vs Nurture is not over, but we might be close to understanding that there is no absolute truth about genotypes and phenotypes. As Dr. Dhar suggested, we are more likely to find trends other than absolute correlations.