Immediately after the attack on the World Trade Centre that day, psychologists predicted that a wave of trauma would sweep across the country.
Although this prediction turned out to be wrong, it is estimated that some 530,000 New York City residents suffered from symptoms of post-traumatic stress disorder (PTSD) in the months following the attack.
those with the largest distress response were the ones born to mothers who were in their second or third trimester when exposed to the World Trade Centre attacks.
How might the traumatic experiences of a pregnant woman be transmitted to her unborn children?
Research published over the past 10 years or so suggests that this probably occurs by epigenetic mechanisms.
Epigenetics is the study of heritable changes in gene activity that are not due to changes in DNA sequence.
Epigenetics reveals how genes interact with environmental factors, and has been implicated in many normal and abnormal brain functions.
A key study in this emerging field, published in 2004, showed that the quality of a rat mother's care significantly affects how its offspring behave in adulthood.
> Simply said, our build, our characteristics are function not only, not simply of genes collection, but also, of a WAY genes are EXPRESSED.
The same genes collection will be expressed differently, through regulation system of genes expresssion, a very delicate, little understood and very complex mechanism.
This makes us all little different, even though we have the same - human - set of genes.
It is a known fact that a genes collection - a genome - of humans and animals, say chimpanzee, and even a fly, is astonishingly similar, 96%.
The first comprehensive comparison of the genetic blueprints of humans and chimpanzees shows our closest living relatives share perfect identity with 96 percent of our DNA sequence,
the chimp and human genomes are very similar and encode very similar proteins.
The DNA sequence that can be directly compared between the two genomes is almost 99 percent identical.
When DNA insertions and deletions are taken into account, humans and chimps still share 96 percent of their sequence.
At the protein level, 29 percent of genes code for the same amino sequences in chimps and humans.
In fact, the typical human protein has accumulated just one unique change since chimps and humans diverged from a common ancestor about 6 million years ago.
Although fruit flies have a genome that is 25 times smaller than the human genome, many of the flies' genes correspond to those in humans and control the same biological functions.