Gene

In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce RNA. There are two types of molecular genes: protein-coding genes and non-coding genes. During gene expression (the synthesis of RNA or protein from a gene), DNA is first copied into RNA. RNA can be directly functional or be the intermediate template for the synthesis of a protein. Genes and their regulatory sequences are mainly responsible for determining the physical traits, or the phenotype of an organism. The genotype is the total amount of DNA in an organism including genes, other functional elements, and non-functional DNA. A gene can acquire mutations in its sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a gene, which may be expressed as different phenotypic traits. Populations evolve when the frequencies of alleles shift due mostly to natural selection and genetic drift. Some of these alleles are located in genes.