Wellington Today Wellington Today 2018 en | Page 14

WELLINGTON SCHOOL LIFE
ACADEMIC EXCELLENCE
OUR BIOLOGICAL
IDENTITY
By Dr Charles Debieux
Head of Science, Wellington College International Shanghai
The Oxford English Dictionary defines the word ‘identity’ as:
‘The characteristics determining who or what a person or thing
is’. In this segment, I wish to address this in a biological sense, an
impossible task in one article, but hopefully this brief overview
will give you a flavour of who we are, genetically speaking.
Deoxyribonucleic acid (DNA) is a chemical which we all have in
our bodies, not located within a specific organ but in the nucleus
of every cell. In short: DNA is the code of life; an instruction
booklet that built you and everyone around you. We are all
linked, every human that has ever existed, by DNA.
Look at the person nearest you. Do they look different? Most
likely they do; they may have differently coloured eyes, hair, skin
pigment, etc, but genetically they are 99.5% identical to you.
That’s right, only 0.5% of your DNA sequence is different to
that of Donald Trump. Scary eh? Well, consider the fact that we
also share a 60% genetic identity (same genes) with chickens!
Although, thinking about it, Donald Trump may share a bit more
than that.
Intellectual
So how does this chemical work? The structure of DNA was
discovered 1953 by Watson and Crick but the true unravelling
of the genetic code did not take place until 2003, after the
completion of the Human Genome Project. This revealed that
DNA is built up of the chemical bases, A, T, G and C, and we call
the order of these bases the DNA sequence. Humans have 2.8
billion of these bases in an order that is 99.5% identical, though as
biologists we prefer to describe it as having 0.5% variation.
This molecule is cut and coiled into chromosomes which fit into
the nucleus of a cell. In fact, if we were to unravel each strand of
DNA from every cell in your body, the resultant material would
be long enough to reach to the moon and back, several times. On
this mega strand there are 25,000 units called genes. These genes
code for proteins, which are how our cells are built, controlled
and maintained and it is at this stage we start to see real variation.
The original theory in Mendelian genetics is that in order to have
variation you need different versions of genes (called alleles). This
holds true today; we all have a gene for eye colour but we have
different versions of this gene. This is the first line in variation:
same gene, slightly different version. Now consider that humans
have 25,000 genes and there are different versions of most of
these (different versions as their code has been changed slightly),
then we start to see where variation occurs.
So why aren’t you a carbon copy of your mother or father?
It’s because you got half of these genes (and thus alleles) from
your mum and half from your dad, which results in variation: a
core principle in Darwinian evolution which states that sexual
reproduction will produce variation.
This is an easy enough concept to grasp: different versions of the
same gene enable variation and sexual reproduction mixes this
up further still, but I bet you still don’t believe that 60% of your
DNA is identical to that of a fruit fly. How organisms can appear
so different, yet have such similar DNA, is a question geneticists
pondered for years.
26