Today I found out that the gene for being Left-handed is dominant while Right-handed is recessive. I personally am left handed and so is my father. My mothers father is also left handed and I was wondering whether or not I am homozygous or heterozygous for the left handed gene. Is there any way to determine this without getting genetic testing or by actually having kids? Thanks. Source: My science teacher

  • $\begingroup$ Welcome to SE Biology. Could you edit your question to include a source showing that there is dominance for left/right handedness? It will allow people to more accurately address your question. $\endgroup$ – Michael_A Jan 19 '17 at 0:23
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    $\begingroup$ Handedness is not determined by a single gene. $\endgroup$ – Imprisoned Rhesus Jan 19 '17 at 4:11

I'm afraid your science teacher is wrong. Handedness is a complex trait. It is not determined by a single gene, and can't be described as being dominant or recessive. Handedness does apparently have a genetic component, but many other factors are involved as well. See the Wikipedia article on handedness:

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 by Medland et al. (2006) has 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, the first by Marian Annett of the University of Leicester and the second by Professor Chris McManus of UCL.

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 locus. From these studies McManus et al. now conclude that handedness is polygenic and estimate that at least 40 loci contribute to determining this trait.

What may be confusing is that the preferred hand is often called the dominant hand, but that usage of the work 'dominant' is unconnected to the concept of dominance in genetics.

  • $\begingroup$ True. However, assuming a single pair trait, as described, the answer to the question asked would be: Nope, can't tell what pattern someone has on a gene pair with a strict dominant/resessive expression unless the recessive is displayed. You would need to check genetics directly or breed enough to get statistical probability on your side. The latter is less certain and would require considerably more patience. Kids can be quite a headache. $\endgroup$ – The Nate Jan 23 '17 at 17:41

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