My daughter is right-handed, but her mother and I are both left-handed. I’ve always thought that handedness is genetic and right-handedness is dominant. My knowledge of genetics hasn’t gone much further than my high school biology class, but I’m recalling that in order for a recessive trait to show up in a offspring, both of the genes received from the parents have to be recessive - i.e. LL instead of RL or LR. Since both parents are LL, where did the R come from? I’m fairly certain that there was no right-handed milkman involved. I’m thinking that this is more complicated than Gregor Mendel’s peapods. Can someone help me understand how this works?
Handedness is not purely genetic, and not a simple “ll Rl RR” paradigm.
The genetic basis of handedness, if any, is still unresolved.
Something like 40% of children of two left-handed people are right-handed like your kid and my brother. (I’m a lefty myself, though)
Anecdotal, but my husband and I are both right handed and so are both sets of parents and everyone else in our families (no lefties in the bunch). And our kid is left handed with everything (writing, sports, buttoning buttons, pool, you name it). No clue about the genetics but it seems to be more complex than, say, eyecolor.
I am the only left-handed person in both my families of descent. So it my spouse.
Just to be clear, if we assume that RH was dominant and LH was recessive*, your anecdote would do nothing to disprove that. It would be no different than two brown-eyed parents having a blue eyed child. Rl x Rl = RR + Rl +Rl + ll.
*probably not true, but that is what the OP is assuming.
In fact, very, very few traits are governed by simple Mendelian rules, with a single gene locus with a dominant version and a recessive version. Most are a combination of a large number of genes, with multiple possibilities for each locus, and some degree of co-dominance. And of course there are also non-genetic influences as well.
An anecdote that would really drive this home would be two left-handed parents who have a right-handed child. That wouldn’t be possible if left-handedness was purely recessive. ll x ll = ll, not Rl, lR, or RR.
My left-handed cousins have a right-handed child.
I’m left handed, but neither of my parents were. I think one grandparent was (but wasn’t allowed to be). My wife is right handed as are both of our daughters. I’m pretty sure that as others have said, it’s not purely genetic.
Actually perhaps more interestingly, I am 100% left handed for one handed activities (writing, throwing, etc.) but 100% right handed for two handed activities (batting, playing guitar, etc.). One of my daughters is left handed using a knife and fork, but nothing else.
(my bolding)
Can I please ask what you mean by being left handed at buttoning buttons? Surely the way you do up buttons is wholly reliant on how the garment is made. Or more likely I have neglected to consider something.
Nobody really has a clue how left-handedness is caused. This is the first time I’ve heard the suggestion that it may be a genetic. Since I’m right-handed, I like to repeat the theory (hypothesis?) I heard many years ago on the news; that that left-handedness is the brain’s way of compensating for minor brain damage at birth due to oxygen starvation. Of course, like any other theory, it is likely completely wrong.
Actually, I suspect the facts that support and disprove this are the same… that lefties often tend to be more creative and smart. Not sure what real-life stats say, but the result may be proof that there was no brain damage, or additional proof that regular functions are being rerouted through unusual pathways with interesting results.
Also, people tend to be left- or right-footed, depending on which foot they tend to lead with; truly awkward individuals are mixed, i.e. left-hand and right-foot.
Note, too, that the recessive/dominant nature of a trait is not really implied by how common or how useful something is. For example, my husband has X-linked hypophosphotemia, which is basically hereditary rickets. It’s a clearly negative trait, and uncommon, but it’s also a dominant trait: there are no carriers. This is possible because it’s caused by a rare mutation that reoccurs on occasion. Presumably it stays rare because people with the disorder tend to reproduce less often, especially in times when it was completely untreatable and when a physical disability was a more serious liability. Therefore, each time the mutation occurs it persists for a few generations and then dies off.
This is also the OP’s case and hence the question.
In summary: Handedness is not as simple as Mendel’s peapods and it is not necessarily based on genetics alone. Thanks for the responses.