Not quite how genes work

The study is a fascinating one, using thousands of brain scans and hundreds of thousands of sequenced genomes to look for associations between genes, brains and hands. It found that, in left-handers, the left and right hemispheres had stronger links in the regions associated with language, which could correlate with greater language ability.

It also found “significant positive correlation” between left-handedness and mental health outcomes such as sensitivity, having “fed-up feelings” and being a “worrier”. Look, I’m no scientist, but that feels extremely real.

Left-handedness runs in families and identical twins are more likely to have the same hand dominant than are fraternal twins and siblings. This implies that the genes do have some influence, but are not the whole story. Previous studies have suggested left-handedness is about 25% heritable, with the other 75% of the variation accounted for by environmental factors – although what those factors are remains elusive.

Err, no.

No, I am not about to insist that I know what causes sinister. Rather, just to make a point about genes.

Yes, inheritable. Sometimes, often, whatever. The trait at least might be inherited, and different ones more strongly or weakly.

Fine.

But that doesn’t mean that something that you parents don’t have is therefore environmental in cause. For there is always that random mutation in each and every generation, isn’t there?

We thus have three – inherit, rising anew through genes/chromosomes/whatever in this generation and environmental causes.

18 thoughts on “Not quite how genes work”

  1. I’m the only left-handed person in the last 4 generations of my extended family, and my incapacity with foreign languages is a matter of legend.

  2. Single-locus genes — where a single gene controls absolutely a single trait — are relatively rare. Most genes control the functioning of other genes, making them more or less likely to be expressed, including completely suppressing them. These are called box genes in the trade. So if there is a rare recessive version of a gene that suppresses another sequence, then two parents that each carry that recessive gene as a heterozygote will each have the phenotype of suppressing said “other sequence” but their offspring has a ¼ chance of receiving the recessive allele from both parents. The result of this is that the sequence that is suppressed in most of the population — including the extended family of both parents if the recessive line is rare enough — will be expressed in the child leading to a trait that doesn’t appear to spring from either parental line.

    Normally we would expect two blue-eyed parents to have a blue-eyed child, but due to a rare-but-not-super-rare box gene, there’s about a 1% chance* of them having a green-eyed child.

    *overall in the population; it will be 0% for most couples and 25% for a few. Generally parents won’t know whether they’re one of the pairs that will throw a 25% chance or not, so while statisticians can grumph about probability vs confidence I’ll leave that argument alone for now…

  3. Never mind the genes biz, the use of “brain scans” for this sort of purpose is a bit dubious. Perhaps it’s better now but some of the early work was rubbish.

  4. @Kevin Lohse & Roué le Jour

    I’m the only left-handed person in the last 4 generations of my extended family, and my incapacity with foreign languages is a matter of legend.

    Similar. My parents, with no previous form, managed to throw 2 left handers out of 3. Both of us are total crap at languages, but we are ace at fixing things.

  5. “But that doesn’t mean that something that you parents don’t have is therefore environmental in cause.”

    Except homosexuality, apparently, according to some.

  6. ‘… identical twins are more likely to have the same hand dominant…’

    Yes, because they are identical! They share exactly the same DNA, unlike non-identical twins or siblings who do not.

  7. mental health outcomes such as sensitivity, having “fed-up feelings” and being a “worrier”

    Those don’t seem to be terribly scientific descriptions. Right up there with “Wednesday’s child is full of woe”…

    I’m a lefty and Wednesday-born. I fear this research will send me into a brown study. We’re like that, you know.

  8. They could just mean epigenetics, which could well be influenced by environment. That identical twins aren’t all the same in this way would seem to strongly hint in that direction.

  9. It’s hard for the outsider to know whether citing “epigenetics” outside the technical literature ever adds up to more than excuse-making and evasion from the Bolsheviks.

  10. Halpern and Coren found that left-handers, on average, live 9 years less that correct-handed people.

    There was an unrelated study decades ago where the researcher suddenly realized that in his large study group there were zero left-handers over 75.

    In my case, Dad was left-handed, and he made it to 90. So I figure my right-handed arse should make it to 99.

  11. @Gamecock
    Interesting, but have they allowed for left-handed children being forced (or, at least, strongly encouraged) to use their ‘correct’ hand, which was certainly still happening (though perhaps already dying out) when I was at school in the 60s. So I’d expect there to be fewer southpaws in older age groups.

  12. My wife and I are both right-handed and brown-eyed and our sons are both left-handed and blue-eyed. Recessive genes have a one-in-four chance and we have provided that chance. [I am fairly close to ambidextrous but not a repressed sinistral, suggesting that left-handedness, like many other genetic factors, is not as simple an on-off as many think]

  13. In ~20% of identical twins, one is left-handed and the other right-handed. I’m struggling to explain that genetically. (Perhaps their DNA twists the other way 🙂 )

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