100 Chapter 3 • The Chromosomal Basis of Inheritance MODEL ORGANISM Neurospora Neurospora crassa was one of the ﬁrst eukaryotic microbes to be adopted by geneticists as a model or-ganism. It is a haploid fungus ( n ± 7) found growing on dead vegetation in many parts of the world. When an asexual spore (haploid) germinates, it produces a tubular structure that extends rapidly by tip growth and throws off multiple side branches. The result is a mass of branched threads (called hyphae ), which con-stitute a colony. Hyphae have no cross walls, so a colony is essentially one cell containing many haploid nuclei. A colony buds off millions of asexual spores, which can disperse and repeat the asexual cycle. Asexual colonies are easily and inexpensively maintained in the lab on a deﬁned medium of inor-ganic salts plus an energy source such as sugar. (An in-ert gel such as agar is added to provide a ﬁrm surface.) The fact that Neurospora can chemically synthesize all its essential molecules from such simple medium led biochemical geneticists (beginning with Beadle and
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.