crassa

Crassa, or Neurospora crassa, is a filamentous fungus commonly known as red bread mold. It belongs to the phylum Ascomycota and is widely used as a model organism in genetics and molecular biology. It exists predominantly in a haploid state and has a brief diploid phase during sexual reproduction. In nature it is a saprotroph, feeding on decaying plant material and other carbohydrate-rich substrates.

Reproduction occurs in two modes. Asexual spores called conidia form on branched conidiophores and disperse in the air; under nutrient limitation, sexual reproduction produces perithecia containing eight ascospores. Neurospora crassa strains used in laboratories are typically haploid and are distinguished by mating types mat A and mat a, which must pair for sexual development.

The species is renowned for Beadle and Tatum's one gene-one enzyme experiments, which used Neurospora to establish a link between genes and metabolic steps. Growth on minimal defined media helped map metabolic pathways because only a defined set of nutrients was required for growth.

Its genome has been sequenced, with approximately 40 million base pairs and around 10,000 genes, providing a resource for functional genomics, circadian rhythm studies, and comparative biology. Neurospora crassa remains a staple in education and research due to its fast growth, straightforward genetics, and well-characterized biology.