The Genetic basis to ‘superhuman’ traits.

By Easha Vigneswaran

The human genome is massive but as humans we still share almost 98% of our genetic material. The interesting part about our DNA is how just 2% in genomic differences is the reason for the vast genetic diversity we observe in human populations. Understanding these differences has governed years of research and scientific study that has led to the increased knowledge surrounding mutations. This has resulted in the discovery of numerous advantageous mutations that have arguably given people ‘superhuman’-like traits not found in the majority of the population.

One of these superhuman traits affects how colour is perceived. The way in which humans see colour is controlled by specific photopigments in our eyes called cones of which humans have three. Known as trichromacy, most of the population can see the same wavelengths of colour and so our colour perception is not too dissimilar. However, there is a small proportion of women who can perceive colour differently (Jordan & Mollon, 2019). A mutation on the X chromosome has resulted in 12% of the female population being tetrachromats where they possess a fourth cone. Typically, the X chromosome carries the genes that encode for the red and green photopigments. These genes encode for opsins (photopigments) more specifically the M and L opsins. Women inherit two X chromosomes and so if the alleles encoding the opsins differ slightly, that may result in varying sensitivity to certain wavelengths (McCrone, 2002). During embryonic development and the segregation of genes, sometimes a ‘mosaic’ of the four cones may arise resulting in a tetrachromat female. It is not to say that these women can see another dimension of colour that trichromats do not, but rather that they are more sensitive to colours and specific hues (Jordon and Mollon, 2019). What is more interesting about this discovery is that it gives us an insight into the visual plasticity of the brain and retina and how it could be manipulated to enhance our anatomical visual systems. 

High bone density is also another trait that many people possess however there are a select few that have such high density that their bones can be considered almost unbreakable. The LRP5 gene was identified as a key gene in regulating bone density in humans (Babij et al., 2009). The gene mutation was originally discovered as a cause for osteoporosis in humans often increasing one’s risk to bone fracturing due low bone density. However, a different mutation in this gene showed the opposite effect – increased bone density. This mutation often resulted in a thickened bone in the jaw that caused high pressure of cranial nerves. Researchers found that people with the mutation had higher levels of fibronectin and osteoblasts which are all constituent molecules for bone formation (Boyden et al., 2002). The findings suggest that though having ‘unbreakable bones’ may just be a result of natural mutation, targeted research on the LRP5 gene could allow scientists to discover specific treatments to prevent early osteoporosis, especially in children. 

A hereditary mutation that was discovered in the Olympic skier Eero Mäntyranta found he had a genetic disorder that increases the red blood cell count due to the elevated production of erythropoietin molecules. The erythropoietin receptor (EPOR) binds erythropoietin (EPO) molecules which is necessary to form new red blood cells. In Mäntyranta, the mutation meant that the EPOR receptor was always on so more red blood cells were produced (Briggs, 2018). The mutation occurs in the EPO gene causing a frameshift. mRNA that is not normally coded for is now transcribed due to the presence of another promoter region. The hyper-production of the erythropoietin means that those with the disorder have more red blood cells allowing for greater oxygen uptake (Zmajkovic et al., 2018). Typically, the transcription of EPO molecules is upregulated in low altitude condition where O2 availability is reduced. However, people with the EPO mutation always have a higher EPO concentration irrespective of the O2 availability hence their increased physical performance (Mairbäurl, 2013).

To conclude, it remains clear there are numerous mutations that have contributed to select enhanced abilities in humans. From super vision to unbreakable bones, the boundaries of human capability are constantly being pushed simply due to minor changes in the genetic code. The discovery of these mutations provides an intriguing insight into the ways we can alter the genetic code to induce more advantageous traits. With the advancements in gene editing technology, it is exciting to consider the possibility of altering disadvantageous traits to create almost ‘superhuman’ ones.

References:

Jordan, G. & Mollon, J. (2019) Tetrachromacy: the mysterious case of extra-ordinary color vision. Current Opinion in Behavioral Sciences. 30 130-134. Available from: https://www.sciencedirect.com/science/article/pii/S2352154619300270. Available from: doi: 10.1016/j.cobeha.2019.08.002. [Accessed May 8, 2021]. 

McCrone, J. (2002) Tetrachromats. The Lancet Neurology. 1 (2), 136. Available from: https://www.sciencedirect.com/science/article/pii/S1474442202000510. Available from: doi: 10.1016/S1474-4422(02)00051-0. [Accessed May 8, 2021]. 

Babij, P., Zhao, W., Small, C., Kharode, Y., Yaworsky, P. J., Bouxsein, M. L., Reddy, P. S., Von Bodine, P., Robinson, J. A., Marzolf, R. A., Bex, F. (2009) High Bone Mass in Mice Expressing a Mutant LRP5 Gene. Journal of Bone and Mineral Research. 18 (6), 960-974. Available from: https://doi.org/10.1359/jbmr.2003.18.6.960 . [Accessed May 10, 2021]. 

Boyden, L. M., Mao, J., Belsky, J., Mitzner, L., Farhi, A., Mitnick, M. A., Wu, D., Insogna, K. & Lifton, R. P. (2002) High bone density due to a mutation in LDL-receptor-related protein 5. The New England Journal of Medicine. 346 (20), 1513-1521. Available from: https://pubmed.ncbi.nlm.nih.gov/12015390/. Available from: doi: 10.1056/NEJMoa013444. [Accessed May 10, 2021]. 

Briggs, S. (2018) The incredible story of Eero Mäntyranta. Available from: https://blog.helix.com/rare-genetics-athleticism-eero-mantyranta/ [Accessed May 10, 2021].

Zmajkovic, J., Lundberg, P., Nienhold, R., Torgersen, M. L., Sundan, A., Waage, A. & Skoda, R. C. (2018) A Gain-of-Function Mutation in EPO in Familial Erythrocytosis. New England Journal of Medicine. 378 (10), 924-930. Available from: https://doi.org/10.1056/NEJMoa1709064. Available from: doi: 10.1056/NEJMoa1709064. [Accessed May 10, 2021]. 

Mairbäurl, H (2013) Red blood cells in sports: effects of exercise and training on oxygen supply by red blood cells. Frontiers in Physiology. 4 332-332. Available from: http://europepmc.org/article/MED/24273518. Available from: doi: 10.3389/fphys.2013.00332. [Accessed May 10, 2021]. 

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