Re: [DIYbio] free food

There's no objective measure of anything, ever. That said, if we call "selective pressure" an objective yardstick, then it's fair enough to say that the rule-of-thumb holds objectively; most stuff that results in a significant loss of "fitness" for an organism's environment or niche without a balancing advantage is either recessive, or weeded out within a few generations, so "most bad stuff is recessive".

Agriculture is an environment. We might be intelligent actors (citation needed) but our selective pressures still weed out "bad stuff" for the niche we force crops to occupy and select for "good stuff". It may be "subjective" in the sense that it's a human applying selective pressure, but from a natural selection POV it's as meaningfully selective as anything else.

And so: the things we value in crops are either fixed by selective pressure, or if they vary then they *may* be dominant or co-dominant, whereas the things we *dislike* in crops are *usually recessive*.

..leading into hybrids, hybrid vigour, and the unfortunate-to-some-advantageous-to-others-but-ultimately-a-side-effect property of hybrids that they do not breed true.

On 15/01/15 19:43, leaking pen wrote:

Good and Bad being completely subjective in this instance as well.

On Thu, Jan 15, 2015 at 12:41 PM, Cathal Garvey

<cathalgarvey@cathalgarvey.me <mailto:cathalgarvey@cathalgarvey.me>> wrote:

    Well, the results suggest the crops are generally a boon,
    particularly to economically marginalised farmers (plenty of data on
    India for eg), but I'll grant you that the marketers aren't exactly
    poster-children and I'm certainly not a fan of theirs.

    As far as Hybrids, it doesn't suit my aesthetics either to have a
    variety that doesn't breed true, but aesthetics be damned: it's a
    rule-of-thumb in genetics that where variation exists in a
    meaningful way, bad things are *usually* recessive, beneficial
    traits are *sometimes* dominant.

    That's simple Darwinism|Mendelianism; if bad things are dominant,
    there is more opportunity for the environment to act selectively on
    them, so they are weeded out faster and leave a pool of less
    damaging alleles, whereas if they are recessive, they can hide from
    selection for a generation or two and may contribute benefit in
    terms of unexpected side-effects, etcetera. So, bad traits that are
    dominant usually work on an organism after it has had a chance to
    breed successfully, which is OK in most agricultural contexts.

    Meanwhile, if things are beneficial, they tend to drift towards
    fixing in the population absent other pressures, until they hit
    equilibrium. If they are recessive, they'll reach some equilibrium
    with other alleles, if they are dominant they are more likely to
    simply become the norm, which means "variation doesn't exist in a
    meaningful way" and the rule-of-thumb ceases to apply. However, if
    only marginally beneficial on their own, beneficial dominant traits
    can take a long time getting to this point.

    Given that bad things are usually recessive and beneficial things
    are not always recessive, and given that breeding creates an
    artificial circumstance of near-total allelic fixation (for a
    defined subset of genes), it stands to reason why Hybrids are so
    popular: when you cross two pure-bred lines, the bad traits that
    limit those lines are usually recessive, and many of the good traits
    are either co-dominant or fully dominant.

    In other words, the F1 generation is often awesome. It's not called
    "carefully selected parental lineages vigour", it's called "hybrid
    vigour". The act of hybridising purebreds *often* or even *usually*
    results in very successful offspring.

    Now, there are two ways to look at this. One is to accept that
    hybrids are awesome and live with the fact that you can then only
    use them for one generation, because they're heterozygotes at most
    relevant loci. The other way is to look at this as inspiration: if
    it is clear which genes are valuable, then engineering a pure-bred
    line with those advantageous traits becomes the goal.

    Right now, we make one or two genetic changes, but with CRISPR and
    next-gen plant engineering, we could hypothetically be making
    "true-breeding hybrids". Hybrids aren't popular because
    manufacturers like DRM'd plants, they're popular because they're
    awesome. So, make them more awesome; make them breed true, and
    (some) farmers will use them.

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