Concept explainers
To review:
The reason behind the restoration of the wild-type
Given:
Two mutant strains of Neurospora (Leu-1 and Leu-2), the wild-type and the fused type were supplied with different nutrient media and their growth was recorded in Table 1. The presence of growth is indicated by the positive sign (+) and the absence of growth is indicated by the negative sign (−).
Table 1: The results of the growth of different strains of Neurospora in different media.
Types of strains used in the experiment | The growth of different strains of Neurospora in different media | ||||
Minimal medium | Minimal medium+2-isopropylmalate | Minimal medium+leucine | Minimal medium+3-isopropylmalate | Minimal medium+α-ketoisocaproate | |
Wild type (haploid) | + | + | + | + | + |
Leu-1 (haploid) | - | - | + | - | + |
Leu-2 (haploid) | - | - | + | + | + |
Fused cells (diploid): Leu-1, Leu-2 | - | + | + | + | + |
The following reaction shows the steps involved in the synthesis of leucine in Neurospora (Figure 1).
Figure 1
Introduction:
Neurospora is an organism that has a single set of the chromosome (haploid) and is able to grow easily under the laboratory conditions. This is the reason due to which it is used as a model organism. The wild-type strain requires minimal medium to grow because they are able to synthesize the essential amino acids, like leucine on their own. The mutant strains like Leu-1 and Leu-2 are unable to synthesize the leucine and are unable to grow on the minimal medium. When the sexual reproduction occurs between two strains, the wild-type phenotype is restored.
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