Genes, DNA, and chromosomes: What's the difference?

THERE are plenty of diseases that I've been told are inherited, something to do with our genes and chromosomes. But I don't really know the difference between DNA, genes, and chromosomes. What is DNA?
DNA is short for deoxyribonucleic acid. It's the hereditary material in all of us and most other living organisms (excluding viruses). Plants have them too, as do bacteria.
In your body, every cell has the same DNA. Most of it is located in your cell's nucleus, which is the command centre of your cell. A small amount is also found in your mitochondria, which are the energy supply powerhouses of your cell. All the information in our DNA is made out of four bases, which are protein. These are adenine (A), guanine (G), cytosine (C) and thymine (T). The order in which these bases are structured - like a very long sentence of words - determine how you are built, like whether or not you are a fish, and what kind of fish.
In humans, 99% of our DNA are the same. That's why we all have a face, two arms, two legs, and all the organs in the right places. The 1% that differs makes us different - and that's why some of us have blue eyes, curly hair, or even certain diseases.
I've heard our DNA is coiled in a double helix. What is that?
The DNA bases pair up with one another like a jigsaw puzzle. A partners up with T because they are physically made to fit together, while C pairs with G.
These bases are attached to a sugar and phosphate molecule called a nucleotide. Paired nucleotides are coiled in two long strands that form a spiral. This is the double (because there two) helix.
Think of it as a curvy ladder.
When your cell needs to divide, this curvy ladder opens up to make an exact copy from the floating bases in your nucleus.
OK, then what is a chromosome?
So, we now understand what goes into our DNA. Now, in the nucleus of our cells, our DNA is packaged into thread-like structures called chromosomes. Think of our DNA as long coiled double helix ladders, which now have to be even more tightly coiled, like a looped skein of thread that is sold in haberdashery shops.
The structure of the chromosome is maintained by proteins called histones.
A chromosome actually looks like a fat sausage that is constricted in the belly. The constriction (or belt) is called the centromere. One arm of the chromosome is longer than the other.
Like DNA, chromosomes are paired with each other. All of us have two sets of chromosomes because one is inherited from our mother, and the other, our father. Each set in every cell contains 23 pairs of chromosomes, which equals 46 chromosomes altogether.
22 out of these 23 chromosome pairs are autosomes. The final pair are sex chromosomes. If you are female, you have XX sex chromosomes. Males have XY sex chromosomes.
What then is a gene?
The chromosome is the biggest unit we have talked about so far. Now the gene is even smaller than the DNA.
In our tightly coiled DNA double helix, there are subunits called genes. If the DNA is one very long sentence, then the genes are the "words" or "phrases" of the sentence.
Each of our genes contain a set of chemical bases, which are the instructions to code a certain protein, which in turn gives rise to a particular trait that we may have.
When our genes want to code for a certain protein, that part of the DNA opens up. The exposed A,T,C,G then attracts complementary bases from the soup swimming in the nucleus. This is called the messenger RNA (ribonucleic acid).
This messenger RNA (mRNA) swims out of the nucleus to our cell's cytoplasm. The mRNA goes to our cells' factory, called the ribosome. The ribosome reads the mRNA and starts assembling the proteins to make whatever is needed. This protein chain goes on and on until the ribosome encounters a STOP sign in the mRNA, called a codon, which is basically an empty sequence.
All this is going on in our bodies even as I type this, and you read this. On and on, with mistakes rarely made. It's the very basis of life itself.
So basically, if a disorder is 'inherited' or 'runs in the family', it's all the genes?
Sometimes. Some disorders like haemophilia or colour blindness which affects multiple members of your family are indeed passed down through gene mutations. Others are not so easy to determine. More often than not, it's a combination of genetics and environmental factors.
This explains why some people, whose genes are primed to get cancer, get cancer, and others don't, and why some people who smoke get cancer, and other smokers never do.