A long lasting relationship between DNA, genes and chromosomes
What is a genome?
The genome carries genetic instructions for the development, functioning, growth and reproduction of all known organisms. We all share more than 99.8% of our genetic heritage with other people. It is precisely the small part of the diversity of our genome that makes each of us unique, different in small ways, eye color, hair color, character, metabolism, etc.. But, at the same time, also very similar to some members of your family: For example, have they told you that you have “your mother’s eyes” or “your father’s nose”?
What are genes?
Genes influence our external appearance and the way the basic processes of our organism work. They contain the information our body needs to produce chemicals called proteins. Proteins form the structure of our body and play an important role in the processes that keep us alive. Genes are made of a chemical called DNA, which is short for “deoxyribonucleic acid”. The DNA molecule is a double helix: two long, thin wires that twist around each other like a spiral staircase. It can make copies of itself. If the two wires are separated, each can be used as a mould to make the other (a new DNA molecule is born). It can carry information. We speak of “genetic code” because the order of the bases along the filament represents a code – a code for protein production.
A gene is a specific sequence of this code that encodes for a specific protein. So, for example, a gene encodes for the insulin protein, which plays an important role in helping your body control the amount of sugar in your blood.
Genes are the basic unit of genetics. Humans have more than 30,000 genes. These genes represent only about 3% of our DNA. The function of the remaining 97% has only a regulatory function, and for the most part it has yet to be studied.
What are Chromosomes?
If we took the DNA of all the cells in our body and unrolled it, from one end to the other, it would form a filament 200 billion kilometers long (a long filament from Earth to Uranus, round trip, but very, very thin!) To store this important material, DNA molecules are tightly packed around proteins called histones to create structures called chromosomes.
Humans have 23 pairs of chromosomes in each cell, for a total of 46 chromosomes. A photograph of a person’s chromosomes, arranged according to size, is called a karyotype.
Sex chromosomes determine whether you are a boy (XY) or a girl (XX). The other chromosomes are called autosomes.
The largest chromosome, chromosome 1, contains about 8000 genes. The smallest chromosome, chromosome 21, contains about 300 genes.