I took Rosa to the Science Museum in London this week, but, if I’m honest, the trip was more for my benefit than for hers.
On the ground floor,
in between the steam engines that powered the industrial revolution and the IMAX
theatre that shows the latest wonders in 3D, is a small exhibit that most
people walk straight past.
Yet it is one of the
most seminal objects in all of science (perhaps in both senses of the word
‘seminal’...).
It is the original
model of the double helix structure of deoxyribonucleic acid - better known as
DNA - constructed by Francis Crick and James Watson in their Cambridge
laboratory in 1953.
Compared to the
molecular models built in labs or simulated on computers today it seems very
antiquated - all clumsy steel rods, plates and bolts. It is not particularly
beautiful but the elegance of nature’s design still shines through. You
can clearly see how the four different bases pair with one another: A (Adenine)
with T (Thymine) and G (Guanine) with C (Cytosine), this being the key to how
the genetic code is replicated in all organisms.
It is one of my
favourite museum pieces anywhere in the world.
The story of the
discovery of the structure of DNA is a classic tale of a frantic race to the
finish in a rapidly evolving field. That Crick and Watson were first past the
post was in no small part helped by the work of Rosalind Franklin, an X-ray
crystallographer (a specialist in interpreting photographs of X-rays scattered
by crystallised substances). The chauvinism of the time meant that her
contribution was downplayed, but nowadays she is recognised properly, albeit
posthumously, for her instrumental role.
Uncovering the
structure of DNA was only the starting point. It turned out that the far
greater challenge was to understand how the code actually works. This is
something with which contemporary genetics still has much further to go.
In a human genome there
are 3.2 billion individual base pairs which, in groups of three, form the 20 or
so ‘letters’ of the genetic alphabet. These are organised into about 20,000
genes - sequences of genetic letters that tell the body how to create the
proteins of which we are made*. The genes are spread across our 23 pairs of chromosomes.
99.7% of our DNA is the
same as the person sitting next to us on the bus or the train. It’s what
makes us human. The remaining 0.3% is what makes us unique (unless you
happen to have an identical twin). As a species, we are far more alike than we
are different.
After Crick, Watson
and Franklin’s discovery of the structure of DNA it would take a further 47
years before the entire genome of the average human was sequenced, also involving
a race to the finish by rival research groups. You may remember the fanfare
around the human genome project in 2000.
Now that has been
done, the individual genes can be identified, and the function of each gene painstakingly
figured out.
This is far from
straightforward. In simple organisms, sometimes there are single genes that map
directly to a physical characteristic (known as a phenotype). For example, whether a tomato is red or
yellow is determined by a single gene.
In humans, the vast majority of phenotypes, such as height or eye
colour, are determined by a combination of genes which may interact in very
complex ways. And of course, for most things such as the risk of developing a
particular condition, many environmental factors are at play as well.
The precise make up of
each gene can vary through random mutations. When an egg is fertilised, the
copying of the genes from parent to child is remarkably precise. But just
occasionally there is an error in a single letter creating a variation of a
gene that can be passed down through further generations. Mutations can also be
introduced by things like excessive exposure to X-rays.
A few of these variations (called alleles) are
known give the carrier an increased risk of developing Parkinson’s. But
carrying them does not guarantee that the disease will manifest itself. Again,
it is the combination of multiple factors, both genetic and environmental, and
perhaps a dose of pot luck, that leads to Parkinson’s.
It is currently thought that around 10% of
Parkinson’s cases have a genetic cause. Given my family history of Parkinson’s
it is highly probable that I am in this group: my mother likely passed some
faulty DNA to me, and her father to her, and his father to him.
There are 24 genes listed by the 100,000 genomes
project on their website as having
alleles, some of them very rare, known to have a strong link to Parkinson’s.
Does my DNA carry one of these mutations? Or
perhaps some new mutation never seen before? Whatever the case, as I was tested only a few weeks ago, it will be quite some time before I find out. But if I do
have faulty DNA there is most likely an even chance that I have passed it on to
my daughter.
I watch Rosa whilst she eats her margarita pizza
for lunch in the museum café. We discuss how the exhibits we have seen that
morning relate to what she has been learning at school in her physics and
biology lessons. She is full of the inquisitiveness and earnestness of youth.
I look into her refulgent brown eyes, unmistakeably
mine. I wonder what else she has inherited from me. Have I cursed her with this disease? She has
a whole life ahead of her, but will her later years be blighted by this
incurable neurological menace?
Surprisingly, I don’t feel guilty about it.
Likewise, I don’t blame my mother for my own
situation.
The eternal paradox of being a parent is that we
cannot** change our children, only strive to give them the best start in life
so that they, we hope, will at least head off in the right direction.
When the time is right, perhaps the best advice I
will be able to give my beloved Rosa is this:
In life we can’t change the hand we are dealt with.
What matters is how we play our cards.
---
* In fact, only about
2% of our genetic material is directly related to encoding proteins. Much of
the other 98% is related to switching individual genes on and off in complex
ways, for example controlling growth in childhood, and some of it is possibly
“junk” DNA, serving no purpose other than to keep replicating itself. The truth
is, geneticists are still trying to figure out what most of our DNA does.
** With genetics, nothing is simple. Nascent research areas like gene therapy raise the possibility of changing our DNA to ameliorate conditions with a genetic causal factor. Then there is the broader debate around neo-eugenics, giving individuals the freedom to make reproductive decisions based on genetic information (as opposed to state sponsored eugenics which has a very troubling history). I may try and tackle these topics, and their ethical implications, in a future post.
** With genetics, nothing is simple. Nascent research areas like gene therapy raise the possibility of changing our DNA to ameliorate conditions with a genetic causal factor. Then there is the broader debate around neo-eugenics, giving individuals the freedom to make reproductive decisions based on genetic information (as opposed to state sponsored eugenics which has a very troubling history). I may try and tackle these topics, and their ethical implications, in a future post.
For a great overview
of the history and the future of genetics, I can highly recommend “The Gene, An
Intimate History” by Siddhartha Mukherjee. Strangely prophetic that Rosa bought me
this book for Christmas….
