Research

Neurospora crassa (Red Bread Mold) as Model Organism for Research

Why would biologists study Neurospora crassa, a filamentous ascomycete commonly known as red bread mold?

First, N. crassa can tell us about other ecologically, industrially, and medically important fungi. Second, N. crassa has the traits that all model organisms share: It is small and easy to grow, and it has a rapid reproductive cycle. Third, this fungus has special advantages for tracing inheritance patterns. Because its hyphae are haploid, N. crassa expresses every recessive or mutated allele in its DNA (in diploid organisms, dominant alleles can mask the presence of their recessive counterparts).

A full accounting of Neurospora’s contributions to basic biology could fill a book. The following list, however, details some ways this fungus has enhanced our understanding of life:

Crossing over

In the 1920s and 1930s, Neurospora provided the first clear evidence of crossing over, which occurs during prophase I of meiosis. Neurospora’s narrow, tube-shaped asci are especially well suited to such studies because they retain the products of meiosis in the original order in which the cells divided.

One-gene/one-enzyme hypothesis

In the 1940s, George Beadle, Edward Tatum, and their colleagues isolated Neurospora mutants with unusual nutritional requirements. Their observation that each mutant had a single enzyme deficiency provided convincing evidence for the idea that one gene encodes each protein in a cell. ∙

Circadian rhythms

Neurospora cultures produce conidia at roughly 24-hour intervals, a phenomenon called a circadian rhythm (circa, “about”; dies, “day”). Mutants that produce conidia constantly or not at all have yielded insights into regulation of the so-called clock-controlled genes.

Gene regulation

Some genes in a cell are “silent” at any given time. Neurospora has helped reveal some of the ways cells regulate gene expression. For example, cells can “tag” DNA with chemical groups that prevent transcription, or they may destroy RNA after transcription.

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