Genes are classified as below:Types of Gene
Britanica Encyclopaedia-chapter-gene, p. 377-78.Genes may function in more ways than known. However, the following categories which are not necessarily mutually exclusive, can be recognized.
1
Message or structural genes
These code for the amino acid sequence of a specific protein through a messenger RNA (mRNA) copy. This carries the coded instructions from the nucleous to the ribosomes, which are the sites of protein assembly in the cell.
2
Operator genes
These signal instructions to regulate the read out or transcription of adjacent message genes. The operator genes in turn may be switched on and off in response to repressor substances, which are products of regulatory genes.
3
Rebosomal RNA genes
These are transcribed into the structural RNA of the ribosomal particles (rRNA) on which protein assembly occurs.
4
Transfer RNA gene
These are transcribed into the diverse transfer RNA (tRNA) molecules that are responsible for tagging and carrying individual amino acids to the ribosome for protein assembly. There are at least 20 kinds of transfer RNA one for each of 20 amino acids. A specific tRNA binds to a specific amino acid and carries it to that part of the mRNA that codes for the particular amino acid in the ribosome.
5
Regulatory genes
These are structural genes whose products are repressors. These act on operator to control the transcription of other genes.
6
Suppressor genes
These reverse the phenotypic of observable, effects of mutations in other genes by a variety of mechanisms.
7
Kinetic genes
These are mixed bag of genes that regulate chromosome movement at cell division. For example, they regulate the centromere of the chromosomes and the initiation of chromosomes replication.
8
Synaptic recognition genes
These drive the unknown mechanism by which homologous chromosome synape (pair off) during the reduction division in higher organisms.
9
Inert genes
In addition to the genes described above the chromosomes contain DNA whose function, if any has not been determined. This DNA may constitute functionless inert genes. It may constitute redundant genes that duplicate other genes in the chromosome. Out of the above all genes the "message gene" is the best understood and most simply explained all of genes. To most people "gene" means message genes. It was only after the discovery of other types of genes that the term "message gene" was adopted. If a protein chain contain 100 amino acid units the messenger mRNA coding for that protein chain would have to be 300 nucleotide pairs long. Such a nucleotide chain would have a molecular weight 2,00,000.[70]