An Idiots Guide
to DNA barcoding - 2.
Genes are made of DNA,
a long molecule that carries information (see figure).

This information is encoded in the sequence
of nucleotides in the DNA, just as the sequence of the letters
in words carries information on a page. The genes are like
short instructions built up of the "letters" of
the DNA alphabet. Put together, the entire set of these
genes gives enough information to serve as an "instruction
manual" of how to build and run an organism. The instructions
spelled out by this DNA alphabet can be changed, however,
by mutations, and this may alter the instructions carried
within the genes. Within the cell, the genes are carried
in chromosomes, which are packages for
carrying the DNA, with the genes arranged along them like
beads on a string. It is the reshuffling of the chromosomes
that results in unique combinations of genes in offspring.
Although such mutations in DNA are random,
natural selection is not a process of chance: the environment
determines the probability of reproductive success. The
end products of natural selection are organisms that are
adapted to their present environments. Natural selection
does not involve progress towards an ultimate goal. Evolution
does not necessarily strive for more advanced, more intelligent,
or more sophisticated life forms. For example, fleas (wingless
parasites) are descended from a winged, ancestral scorpionfly,
and snakes are lizards that no longer require limbs - although
pythons still grow tiny structures that are the remains
of their ancestor's hind legs. Organisms are merely the
outcome of variations that succeed or fail, dependent upon
the environmental conditions at the time.
The understanding of evolutionary biology
began with the 1859 publication of Charles Darwin's
On the Origin of Species.
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