Neurospora crassa

 Neurospora crassa  is a type of red bread mold of the phylum Ascomycota. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons.

N. 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. 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. 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 to the "one gene, one enzyme" hypothesis that states that specific genes code for specific proteins.

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.