The gene is the basic functional unit of heredity. Genes are made up of deoxyribonycleic acid (DNA) or in the case of some viruses they are made up of ribonucleic acid (RNA). They contain particular set of instructions as coding for specific proteins or function. They determine an observable trait or characteristic of an organism and the DNA sequence that determines the chemical structure of a specific polypeptide molecule or RNA molecule. The word ‘gene’ was invented by W. Johannsen in 1909 but the modern concept of the gene originated with Gregor Mendel, who in the 1860s studied the inheritance of characteristics that differed sharply and unambiguously among true-breeding varieties of garden peas. Mendel found that a hybrid between two phenotypically distinct varieties resembled one of the two parents – the dominant parent.

In humans, genes vary in size but the Human Genome Project estimated that humans have between 20,000 and 25,000 genes. The entire DNA in the cell makes up the human genome and every person has two copies of each gene, one inherited from each parent. The DNA in the genes makes up only 2% of the genome and most genes are the same in all people but a small number are slightly different between people. Genes contain hundreds of thousands of chemical bases and alleles are forms of the same gene with small differences in their sequence. These small differences contribute to each person’s unique physical features (phenotype). Even though a trait may not be observable, its gene can still be passed on to the next generation. This is known as a recessive gene. A gene that is always exhibiting a trait from one generation to another without suppression is known as a dominant gene. However, some genes are referred to as non-coding genes because they do not appear to contain information that the cells can use and produce. Contrary to popular belief, they are not functionless but their roles are slowly being discovered.

The idea that genes are also responsible for the manufacture of proteins was first proposed in 1902 by Sir Archibald Garrod, who realized that alkaptonuria was an inherited metabolic condition in humans and hypothesized that it was due to the absence of an enzyme (a catalytic protein) required for the breakdown of homogentisic acid. Systematic investigation of the relationship between genes and enzymes did not occur until 1941. It was later realised that in order to make proteins, the gene is copied by each of the chemical bases into the messenger ribonucleic acid (mRNA). The mRNA moves out of the cell nucleus and uses ribosomes to form the polypeptide that configures to form the protein.

All information about the sequences and genes discovered in the human body are carefully recorded and the all the information is placed in a database that is publicly available. Some DNA that have not been sequenced are also available and any scientist can sequence it and post the findings in the same database from anywhere around the world.

January 16th, 2014

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