This post was instigated by the sheer sense of awe evoked by the sentence,
“Over
half of all known disease mutations come from replacement polymorphisms.”
My attempt to share the awe ensues below.
Scientifically, the basis of all
human beings is DNA, which exists as a double stranded helix, meaning two strings
of molecules wrapped around each other. The human genome comprises in excess of
3,000,000,000 (3 billion) pairs of molecules and these molecules are constantly
being replicated as cells die and new cells are needed to replace them. Not to
mention that the molecules replicate at around 50 molecules
per second per strand of DNA. Now imagine that happening in multiple places
in one cell and then in multiple cells in one person at any given point in
time. That’s an incredible amount of work just to survive day to day as a fully
functioning homo sapien.
A lot of diseases, including
cancer, arise from incorrect molecules being introduced into the DNA sequence
during replication. Out of these “mistakes”, a fair amount don’t really make a
difference because of certain redundancies in the way the cells interpret the
DNA. Sometimes, only one molecule in the entire sequence is different- a single
nucleotide polymorphism (SNP). What the sentence quoted at the very beginning
is saying is that half of all genetic mutations, or “mistakes”, that are known
to cause diseases happen because one molecule (in 3 billion molecules) was
copied incorrectly. Essentially if a cell is 99.99999997% accurate in
replicating its molecular basis, you can get cancer (if the mistake is in the
right place).
Considering that most people don’t
have major genetically induced diseases despite having way more than just one
cell (60-90
trillion, to be more accurate), the human body is way awesome in terms of accuracy of replication. Imagine if you
were wrong only once out of three billion attempts, you’d get through school,
bachelors, masters and PhD without once having been wrong in an exam (or being
wrong only once if the probabilities didn’t work out in your favor)! See- awesome! :)
