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Posted by bio_man   June 26, 2017   2981 views

Approximately 10% of the world population is left-handed. What causes this anomaly?

While there are several theories that try to explain this trait -- such as the positioning of the baby during the final trimester, hormone exposure during pregnancy, or epigenetic factors -- the most consistent and hardwired explanation boils down to plain old genetics. In other words, the reason you're right-handed or left-handed is because it's written in your DNA.

Research suggests that handedness displays a complex inheritance pattern. For example, if both parents of a child are left-handed, there is a 26% chance of that child being left-handed. A large study of twins from 25,732 families also indicated that the heritability of handedness is roughly 24%.

To date, two theoretical single gene models have been proposed to explain the patterns of inheritance of handedness. However, the growing weight of evidence from linkage and genome-wide association studies suggests that genetic variance in handedness cannot be explained by a single genetic location. Rather, handedness appears to be polygenic, and is possibly determined by 40 different genes acting on this one trait!

Source 1) McManus, Chris (2003). Right Hand, Left Hand.
2) Medland, SE; Duffy, DL; Wright, MJ; et al. (January 2009). "Genetic influences on handedness: Data from 25,732 Australian and Dutch twin families". Neuropsychologia. 47: 330–337.

left-handed right-handed genetics epigenetics brain
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