what is gene

A gene is the basic physical and functional unit of heredity. It is a small section of DNA that contains the instructions for a specific molecule, usually a protein. Genes are passed from parents to offspring and contain the information needed to specify physical and biological traits. Each chromosome contains many genes. There are two types of genes: Mendelian genes and molecular genes. The Mendelian gene is a basic unit of heredity, while the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function. Some genes act as instructions to make molecules called proteins, while many genes do not code for proteins. Genes come in different forms, called alleles. In humans, alleles of particular genes come in pairs, one on each chromosome. If the alleles of a particular gene are the same, the organism is described as homozygous for that gene. If they are different, the organism is described as heterozygous for that gene. An individual’s phenotype is determined by the combination of alleles they have.