Not wet mud
Not sea kelp
A
One of the triumphant implications of Maxwell’s theory was an
understanding of the nature of light. Rather than a distinct kind of
substance, light is a propagating wave in the electric and magnetic fields,
also known as electromagnetic radiation. We think of electromagnetism as
a “force,” and it is, but Maxwell taught us that fields carrying forces can
vibrate, and in the case of electric and magnetic fields those vibrations are
what we perceive as light. The quanta of light are particles called photons,
so we will sometimes say “photons carry the electromagnetic force.” But at
the moment we’re still thinking classically
A
Although a small fraction of nonsynonymous mutations are advantageous
or neutral, many are harmful: they impair protein function, often affect physiological or morphological characteristcs, and reduce individuals’ survival or
reproduction. For this reason, they tend not to persist in species populations,
and so genes evolve more slowly by nonsynonymous mutations than by synonymous substitutions. The genome also has a lot of noncoding DNA, some
of which appears to be nonfunctional and which also evolves rapidly, like synonymous mutations, by genetic drift. These differences are important for
phylogenetic studies because rapidly evolving parts of the genome provide
information on relationships among species that diverged over a short time
interval in the recent past. (I mean “short” and “recent” by geological standards, namely hundreds of thousands of years!).
a
No comments:
Post a Comment