What do you think about the saying
DNA determines you?
DNA is regarded as the code of life
The biological information
is hidden in the DNA sequence
Does it mean that
DNA sequence determines you?
Let's look at the following cases
First
we are all developed from fertilised eggs
The cells divided thereafter
have the same DNA sequence
If the hidden biological information
is the same
how can these cells
develop into different cell types?
The DNA sequence in different tissues
is the same
why do cells in different tissues
have different functions?
The DNA sequence in the eye cells
and stomach cells is the same
why don't the eye cells produce
gastric acids as the stomach cells do?
Another case is identical twins
A fertilised egg replicates itself
The divided cells
develop into two individuals
and their DNA sequence is identical
Does it mean that
these twins are identical in all aspects?
Identical twins
are very similar to each other
but there are still some differences
What causes these differences?
The above cases show us that
even with the same DNA sequence
the characteristics expressed are different
But why?
To think about these questions
we must understand
the mechanism of gene expression
and its regulation
In gene expression
the biological information
is transcribed into RNA sequence
and then translated into amino acids
which form the proteins
responsible for different cell functions
metabolism
and the characteristics of the organisms
However
all the twenty thousand genes in our cells
are not expressed at the same time
Every step of gene expression
has precise and complicated mechanisms
like switches
to control the degree of
expression of these genes
The genes can be non-expressed
slightly expressed or over expressed
For example
a process called DNA-methylation
is important
for the regulation of gene expression
When genes are combined with methyl groups
the structure of DNA molecule is altered
Then the genes cannot be transcribed
and thus
they cannot be expressed
When a fertilised egg
divides and differentiates
throughout the entire process
of embryo development
the genes in every cell
at different stages and time
are controlled by various mechanisms
which cause differential expression
of the genes in different cells
The cells can thus undergo
differentiation and develop
into different cells tissues and organs
As a matter of fact
gene regulation
is influenced by environmental factors
For example
if a pregnant woman
consumes alcoholic drinks
alcohol will affect
the development of the embryo
Scientific research using
human embryonic stem cells showed that
alcohol increases DNA-methylation
of many genes
The expression of genes
controlling cell differentiation is altered
which may result in
abnormal embryo development
Scientific studies also showed that
when comparing the heavy drinkers
with those who do not drink
there is a 20% difference
in DNA-methylation in their brain cells
The gene expression patterns
between them are also different
which may account for
weak memory and addiction
If two identical twins living
in the same family
enter two different hostels in university
One of them enters a hostel which has
a long tradition of drinking alcohol
the students there
drink a lot of alcohol during night talks
The other one enters a hostel
without such tradition
the students there
drink only water during night talks
Do you think the identical twins
having the same DNA sequence will gradually
develop different characteristics?
We know that a change in DNA sequence
may cause a change
in the expressed characteristics
However
when the DNA sequence remains unchanged
there are still many precise
and complicated mechanisms
to control the expression of every gene
which also causes a change
in the expressed characteristics
Gene expression is affected by different
factors either directly or indirectly
These factors include
the bio-molecules produced by cells
the nutrients in diets
chemicals and radiations in the environment
stress and habits
etc
In fact it is impossible that two people
are affected by the same factors
Therefore
even if their DNA sequence is identical
the results from their gene expressions
are different
These differences may be
very small at the beginning
but they will become more obvious over time
In fact
from the time of pre-natal stage to death
we are all affected by the
biological information hidden in DNA
and its interaction with
various environmental factors
If this is true
when someone argues
DNA determines you
What would you say?
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