BOTANY Higher Secondary Second Year - Textbooks Online

3.2. Gene and genome
The word gene was coined by W. Johannsen in 1909. A gene is a
physical and functional unit of heredity. It carries information from one
generation to the next. Gene is also defined as a nucleotide sequence that
is responsible for the production of a specific protein. When a gene
undergoes changes due to mutation, it results in biological variations.
These variations are important for evolution. Such variations also arise
due to recombination of genes on chromosomes.
The relationship between genes and enzymes was discovered by Beadle
and Tatum. They conducted bio-chemical research on the fungus
Neurospora and concluded that the major role of genes was to carry
information for the production of enzymes. For their work they were
awarded Nobel prize in 1958. Their findings are referred to as ‘one gene
one enzyme hypothesis’. Now, the hypothesis has been modified to ‘one
gene one polypeptide hypothesis’ because the product of gene action is
always a polypeptide.
Genome
Genome may be defined as the totality of the DNA sequences of an
organism including DNAs present in mitochondria and chloroplasts. Each
species has a characteristic number of chromosomes in the nuclei of its
gametes and somatic cells. The gametic chromosome number constitutes
a basic set of chromosomes of the organism. In all organisms it is made
up of DNA but in viruses, it is made up of either DNA or RNA.
Table showing the organisms and their haploid set of chromosome
Sl.No. Name of organism
Haploid set of
chromosome
1. Arabidopsis thaliana 5
2. Garden pea 7
3. Paddy 12
4. Triticum aestivum 21
5. Homo sapiens 23
6. Chimpanzee 24
7. Sugarcane 40
8. Ophioglossum
114
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