Re: Histones


and they play a role in gene regulation

May histones, and the way DNA is wrapped around it, not be compared
to, for example, the adjustment-knob of a microscope?

The turning of the knob on a microscope results in a predictable
change in another part of the system: the positioning of the lenses,
and also in the overall functioning of the microscope: its focussing
on a particular object. Because of this, applying change in this way
is a rather safe and controlled affair.

In the same way, one might imagine that a change in the way DNA is
wrapped around histones (perhaps related to the length of a piece of
non-coding DNA) is directly correlated with a change of some
phenotypic effect (say leg-length.) Because of this the scope of
mutation will be limited; it will result in a slight, quantitative
change in a particular trait.


The adjustment-knob of a microscope is a designed feature, its
function being the fine-tuning of focus.

In analogy, histones, and the way DNA is wrapped around it, may be an
adaptation, a feature shaped by natural selection, its function being
the introduction of variation in a controlled and measured way,
allowing for the fine-tuning of the organism.


(the last point, evolution for the sake of evolvability, probably
involves group-selection, which is problematical)


.

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