What is Gene?
The characters of a species are transmitted without much change from one generation to another. One inheritance pattern of characters indicates that their expression is controlled by genes which are located on chromosomes and constitute total genomic make-up of the organism. A gene is a unit of information that directs the activity of the cell or organism during its lifetime. It passes message along to the progeny when the cell or organism divides or reproduces.
Properties of Genes
Gene
The main properties of genes are may be noted as follows: -
i) Gene determines the physical and metabolic characteristics of the cell and is responsible for transmission of characteristics from one cell generation to the other.
ii) Genes are situated in chromosomes.
iii) There are several genes in each chromosome.
iv) Every gene occupies a fixed position in the chromosome.
v) They are arranged in a single linear order in a chromosome.
vi) A single gene may occur in several different forms called alleles. Many genes have only two alleles, each of which controls an alternative expression of the same trait. The two alleles of a gene may frequently be related to each other as dominant and recessive.
vii) A gene may show a sudden change from one form to another. Such a change in form is called mutation and new allele thus formed is known as mutant.
viii) Genes on one chromosome may be transferred to another as a result of crossing over during meiosis or due to translocations.
ix) Doubling-up of a chromosome during mitosis is preceded by self-duplication of genes of that chromosome.
x) They express themselves through the production of proteins (enzymes) which control cell metabolism.
Gene Functions
It should perform at least three functions to qualify itself to be a gene. Those three functions are as follows whish are very easy to realize: -
i) It should be able to replicate and be inherited by the progeny faithfully.
ii) It should be susceptible to an occasional change by way of mutation and such a change should be stably inherited.
iii) It should be able to carry all the information necessary to program the functions of a cell.
Nature of Gene
After the establishment of' gene concept biologists concentrated their efforts to find out chemical component of chromosomes which constitutes the actual genetic material. As early as 1869, a Swiss biochemist, Friedrich Mischer, from separated nuclei from pus cells isolated a new class of organic compounds which he called nuclein. It was renamed as nucleic acid by Altmann in the year1889. By 1920, it became clear that chromosomes are made up of macromolecules of two biological compounds— proteins and deoxyribonucleic acid (DNA).
However, there was substantial controversy whether one or both of these constituents are the actual carrier of genetic information. Proteins being the most complex, their complexity and variety led many biologists to believe that they are the determinants of varied characters encountered with in the living world. It was later found that it is not the protein molecule but DNA which is remaining in the gene as a genetic material. A study of diverse organisms revealed that while nucleic acids are only of two types, there are countless kinds of proteins.
This created doubt regarding the claim of nucleic acid instead of proteins as the hereditary material. Now, it has been proved beyond doubt that genetic information is stored in nucleic acids of the cell.