the work went into mapping and cloning the gene through association studies and chromosome walking. Despite being laborious and costly, forward genetics provides a way to obtain objective information regarding a mutation's connection to a disease. Another advantage of forward genetics is that it requires no prior knowledge about the gene being studied. Cystic fibrosis however demonstrates how the process of forward genetics can elucidate a human genetic disorder. Genetic-linkage studies were able to map the disease loci in cystic fibrosis to chromosome 7 by using protein markers. Afterward, chromosome walking and jumping techniques were used to identify the gene and sequence it. Forward genetics can work for single-gene-single phenotype situations but in more complicated diseases like cancer, reverse genetics is often used instead. This is usually because complex diseases tend to have multiple genes, mutations, or other factors that cause or may influence it. Forward and reverse genetics operate with opposite approaches, but both are useful for genetics research. They can be coupled together to see if similar results are found. Classical forward genetics By the classical genetics approach, a researcher would then locate (map) the gene on its chromosome by crossbreeding with individuals that carry other unusual traits and collecting statistics on how frequently the two traits are inherited together. Classical geneticists would have used phenotypic traits to map the new mutant alleles. Eventually the hope is that such screens would reach a large enough scale that most or all newly generated mutations would represent a second hit of a locus, essentially saturating the genome with mutations. This type of saturation mutagenesis within classical experiments was used to define sets of genes that were a bare minimum for the appearance of specific phenotypes. However, such initial screens were either incomplete as they were missing redundant loci and epigenetic effects, and such screens were difficult to undertake for certain phenotypes that lack directly measurable phenotypes. Additionally, a classical genetics approach takes significantly longer. History Gregor Mendel experimented with pea plant phenotypes and published his conclusions about genes and inheritance in 1865. Around the early 1900s Thomas Hunt Morgan was mutating Drosophila using radium and attempting to find heritable mutations. Alfred Sturtevant later began mapping genes of Drosophila with mutations they had been following. In the 1990s forward genetics methods were utilized to better understand Drosophila genes significant to development from embryo to adult fly. In 1995 the Nobel Prize