Forward genetics is a molecular genetics approach of determining the genetic basis responsible for a phenotype. Forward genetics provides an unbiased approach because it relies heavily on identifying the genes or genetic factors that cause a particular phenotype or trait of interest. This was initially done by using naturally occurring mutations or inducing mutants with radiation, chemicals, or insertional mutagenesis (e.g. transposable elements). Subsequent breeding takes place, mutant individuals are isolated, and then the gene is mapped. Forward genetics can be thought of as a counter to reverse genetics, which determines the function of a gene by analyzing the phenotypic effects of altered DNA sequences. Mutant phenotypes are often observed long before having any idea which gene is responsible, which can lead to genes being named after their mutant phenotype (e.g. Drosophila rosy gene which is named after the eye colour in mutants). Techniques used in Forward Genetics Forward genetics provides researchers with the ability to identify genetic changes caused by mutations that are responsible for individual phenotypes in organisms. There are three major steps involved with the process of forward genetics which includes: making random mutations, selecting the phenotype or trait of interest, and identifying the gene and its function. Forward genetics involves the use of several mutagenesis processes to induce DNA mutations at random which may include: Chemical mutagenesis Chemical mutagenesis is an easy tool that is used to generate a broad spectrum of mutant alleles. Chemicals like ethyl methanesulfonate (EMS) cause random point mutations particularly in G/C to A/T transitions due to guanine alkylation. These point mutations are typically loss-of-function or null alleles because they generate stop codons in the DNA sequence. These types of mutagens can be useful because they are easily applied to any organism but they were traditionally very difficult to map, although the advent of next-generation sequencing has made this process considerably easier. Another chemical such as ENU, also known as N-ethyl-N-nitrosourea works similarly to EMS. ENU also induces random point mutations where all codons are equally liable to change. These point mutations modify gene function by inducing different alleles, including gain or loss of function mutations in protein-coding or noncoding regions in the genome. Radiation mutagenesis Other methods such as using radiation to cause large deletions and chromosomal rearrangements can be used to generate mutants as well. Ionizing radiation can be used to induce genome-wide mutations as well as chromosomal duplications, inversions,