Nucleic acids- 41 Genes A gene is a segment of DNA that contains the instructions for making a particular protein (or a set of closely related proteins). Although this definition holds for the majority of genes, several percent of genes produce an RNA molecule, instead of a protein, as their final product. Like proteins, these RNA molecules perform a diverse set of structural and catalytic functions in the cell. Gene occupies a specific position (locus) on DNA. Total gene numbers range from less than 500 for simple bacteria to about 25,000 for humans. Genome It is the total number of genes within one mature cell of an organism. The human genome contains about 20,000 to 25,000 genes present along the 23 pairs of chromosomes (46 chromosomes). The genome of somatic cell is diploid i.e. it contains twice the normal gametic number of chromosomes. In man, the somatic cell contains 23 pairs one chromosome is derived from father (parental) and the other is derived from mother (maternal). Types of genes a) House keeping genes: These are essential for life of the cell. These are integral parts of the cell . They perform essential function to cell e.g. energy creating enzymes. b) Differential (specific function) gene: It performs specific functions in the cell. It differs in each organ according to the function. Alleles These are alternative forms of a gene found at the same locus on a specific chromosome. Each character is controlled by a pair of genes that occupy the same position (locus) on homologous chromosomes. Each one of these genes is known as allele i.e. gametic variant. A pair of alleles may be identical, and is called homozygous or different, and is called heterozygous. One of the two alleles determines its character, so it is called: dominant allele and the other one is called: recessive allele
Posted on: Tue, 02 Dec 2014 08:07:59 +0000
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