And what is DNA?

DNA (deoxyribonucleic acid) is a molecule which contains the biological instructions that makes each of us unique. DNA, along with the instructions it contains, is passed from adult organisms to their offspring during reproduction.
Our bodies are made from billions of individual cells and DNA is the control center for each and every cell. It is present in each cell in the form of a number of chromosomes. Chromosomes are arranged in pairs and the two members of each pair are almost identical copies of one another.

The mass of DNA is surrounded in most cells by a strong membrane with tiny specific openings, which will, like a security guard, allow some items to enter or leave, whilst keeping others on the inside or the outside.
Important chemical molecules go in and out of these holes. The space in the cell that is not occupied by DNA and the various sorts of machinery is filled with water.

The DNA contains all the genetic information needed for construction of a human being. Growth occurs by the process of cell division. Each cell divides into two cells and these cells in turn divide, and so on. Just before any cell divides, it duplicates its entire DNA, so that every new cell contains a complete set of DNA, which again contains all the genes of the organism.

Only a small fraction of all the genes present on this DNA are activated in any given type of cell. Thus cells that develop into an eye use only the genes that program for the growth of eye-cells. How cells know which kind of organ they belong to still being researched.

The DNA of humans is composed of approximately 3 billion base pairs of cells, making up a total of almost a meter-long stretch of DNA in every cell in our bodies. So as to be able to fit, the DNA needs to be in a very compact form. The human DNA is packaged in to 23 distinct chromosome pairs. (link to “What is a Chromosome”)

So we now know or knew that all of us started as a single fertilized egg in our mother’s Fallopian tubes. Then, over the following 9 months or so, that cell grew, through a process of repeated cell division, into a fully formed newly born human being, with a brain, organs, limbs, muscles and a voice.

The questions of how this process takes place - how the fertilized cell knows what it is supposed to do and how it does that – is the big question.
However we are not going to tackle that research here even if we could.

What we do know is that together, these cells must form a total of ten trillion connections with the brain, and in almost every baby ever born this is done correctly. All of this is accomplished through the functioning of DNA, the computer program that runs through every living organism on earth – plants, animals and mankind.
DNA contains the biological instructions that make every species unique. DNA contains the instructions that are passed on from adult organisms to their offspring and again to their offspring during reproduction.