The Molecular Biology Notebook OnlineYou are here: >
Neurospora crassa
Neurospora is classified in the phylum Ascomita.
With about 30,000 known species, the Ascomycetes are the largest group of fungi. Unlike the Basidiomycetes, in which the spores develop externally, ascomycete fungi produce their spores inside a sac (ascus), usually within fruiting bodies generally known as 'ascomata'.
Neurospora's mycelium consists of branching hyphae
divided by the occasional
cross wall called a septum.
 (1) Ascospores
are produced from special hyphae with just two nuclei per cell: |
 (2) The
last cell of the hyphae forms a Hook (Hook cell) : |
 (3) Both
nuclei undergo a division. The result is a hook cell with four nuclei. |
 (4) Then
the cells divide, and the hook locks. The cell wall between what was the
hook and the original cell disappears. |
 (5) The nuclei
in the top cell fuse to form a zygote. |
 (6) The zygote
nucleus then starts meiosis. The first part of meiosis leads to the
formation of two nuclei that each contain n chromosomes. |
 (7) The second
part of meiosis leads to four nuclei each with n chromosomes. There
is no separation of cells. |
 (8) Instead,
all the nuclei undergo a proper mitosis. (There must be a replication of
the DNA between these two steps) |
 (9) A membrane
forms around all the eight nuclei and the eight new spores are ordered
nicely. |
 |
All this happens in a special structure: the fruiting body.
When an ascus is mature, it discharges the ascospores into the air, where
winds and currents carry them to colonize other areas.
|
Neurospora crassa has been a useful tool in genetics: think about what is interesting about such an organism:
This fungus can be grown easily on a minimum medium containing only sucrose, inorganic salts, and biotin (growth factor).
Why is it such an advantage for research?
How long is the diploid state compared to the haploid state?
What is the interest in having a haploid organism when studying genetics?
Why is the spore formation so particular and interesting?
Would it be possible to see the ascospores in the ascus?
What is the advantage in a short life cycle?
This fungus can be grown easily on minimum medium : sucrose, inorganic salts, and biotin (growth factor). Why is it such an advantage to research? This organism is able to live on a minimal medium. It means that it has all the metabolic machinery to make all the necessary nutrients from a minimal resource. See the picture of a culture of a fungi in a petri dish
How long is the diploid state compared to the haploid state? Neurospora crassa is a fungus. It is only when the nuclei fuse that one sees a diploid state, so the diploid state is very brief. The normal hyphae have up to ten nuclei, each being haploid.
What is the interest in having an haploid organism
when studying genetics? In an haploid state, recessive mutations
are expressed, and the phenotype reflects the genotype of the cell.
Why is the spore formation so particular and interesting? The spores are ordered, and stay in order. It is possible to dissect individual spores.
Would it be possible to see the ascospores in the ascus? One can see the ascospores with binoculars. A magnification of x40 is needed.
What is the advantage in a short life cycle? It is easy to obtain successive generations of spores. In a fly, the life cycle is fifteen days. For fungi it can be few hours. What is the life cycle of humans? Do you understand why human genetics is so difficult?
Tweet
Neurospora on Wikipedia
Neurospora at Answers. com
Related Links
-Beadle, George Wells...they began the study of the development of eye pigment in Drosophila which later led to the work
-One Gene - One Enzyme Theory
This led them to postulate the one gene - one enzyme theory: each gene in an organism controls the p
-Tatum, Edward Laurie
...when he and Beadle decided to give up their work on Drosophila and to work instead with the fung