What exactly is a genetic system? In this instance, it means that
living things are able to reproduce in a way that passes
features, or at least information about making features, along from a
parent to its offspring. For living things on the planet Earth,
this feature is usually based on information stored in
Acid, or DNA. Genes are made of
the material DNA, and this is the
basis of the term "genetic." This molecule holds the code by which proteins are
made - and proteins are the workhorse molecules of earthly organisms.
But features can be passed along in non-DNA ways - some
features found in your cells are there because they were in your mother's egg
cell, and some of your traits and tendencies may be linked to the
chemistry that surrounded you in the womb while you developed.
Another type of example would be this book, and all of the sorts of
information that can be passed on through learning. Inheritable traits that are not strictly in our DNA
code are called memetic
- later, when things like evolution are discussed in terms of passing on
traits, this is something to remember: all that we are, all that we
pass on is not just in our DNA codes. This also opens the door for many
of what we might call machines to have this aspect of life - is
transferable computer code a genetic system?
Embedded in this feature of Life is reproduction
- it's hard to pass traits on to offspring without reproducing. You could
probably imagine a living thing that never ages (and, to survive, is really lucky) and never
reproduces, but no one has found such a thing. In our world, living
things reproduce, and
reproduction falls mostly into two camps: asexual
where offspring are genetic copies of the parent (they can
be genetic copies yet not
to be physical copies, because of how genes work), and sexual
reproduction, where offspring are a mix of gene sets from two
sources (and which may or may not involve two separate
parents). You might not think so by looking at these definitions,
but there is a gray area between these types as well, where copying
happens but some mixing is allowed. As we'll see later, there are
advantages to each and disadvantages to each (that is a trend you should
be noticing in many kinds of biology pairs, the advantage of
one reflects upon the disadvantage of the other).
A side effect of reproduction is growth and
development: without growth, each generation would get
progressively smaller beyond their ability to survive; without
development, the next reproduction phase could not be timed properly.
Growth is a fairly simple property, while development can be a simple
switch in a cell that says, "Don't divide yet," or the many
complicated stages that multicellular organisms go through between one zygote
(the very first cell, usually created from the fusion of a sperm and
an egg cell) and the next generation's zygote-generating adult.
features, discussed in more detail elsewhere, are temporary
modifications of DNA, usually methyl groups "clipped" near genes, that
allow the genes to be activated and deactivated; these can be
passed from cell to cell and from parent to offspring in their
modified form, although typically most of the clips are stripped off
as a preparation for reproduction.
An old biology proverb states that, "An adult is
just a zygote's way of making another zygote." You might have
heard a variation: "A chicken is just an egg's way of making