Neurospora crassa is a type of red bread mold of the phylum Ascomycota. The genus name, meaning "nerve spore" in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestation of French bakeries in 1843. Neurospora crassa is used as a model organism because it is easy to grow and has a haploid life cycle that makes genetic analysis simple since recessive traits will show up in the offspring. Analysis of genetic recombination is facilitated by the ordered arrangement of the products of meiosis in Neurospora ascospores. Its entire genome of seven chromosomes has been sequenced. Neurospora was used by Edward Tatum and George Wells Beadle in their experiments for which they won the Nobel Prize in Physiology or Medicine in 1958. Beadle and Tatum exposed N. crassa to x-rays, causing mutations. They then observed failures in metabolic pathways caused by errors in specific enzymes. This led them to propose the "one gene, one enzyme" hypothesis that specific genes code for specific proteins. Their hypothesis was later elaborated to enzyme pathways by Norman Horowitz, also working on Neurospora. As Norman Horowitz reminisced in 2004, "These experiments founded the science of what Beadle and Tatum called 'biochemical genetics'. In actuality, they proved to be the opening gun in what became molecular genetics and all developments that have followed from that." In the 24 April 2003 issue of Nature, the genome of N. crassa was reported as completely sequenced. The genome is about 43 megabases long and includes approximately 10,000 genes. There is a project underway to produce strains containing knockout mutants of every N. crassa gene. In its natural environment, N. crassa lives mainly in tropical and sub-tropical regions. It can be found growing on dead plant matter after fires. Neurospora is actively used in research around the world. It is important in the elucidation of molecular events involved in circadian rhythms, epigenetics and gene silencing, cell polarity, cell fusion, development, as well as many aspects of cell biology and biochemistry. The sexual cycle Sexual fruiting bodies (perithecia) can only be formed when two mycelia of different mating type come together (see Figure). Like other Ascomycetes, N. crassa has two mating types that, in this case, are symbolized by A and a. There is no evident morphological difference between the A and a mating type strains. Both can form abundant protoperithecia,