After irradiating wild-type cells of Neurospora (a haploid...

After irradiating wild-type cells of Neurospora (a haploid fungus), a geneticist finds two leucine-requiring auxotrophic mutants. He combines the two mutants in a heterokaryon and discovers that the heterokaryon is prototrophic. a. Were the mutations in the two auxotrophs in the same gene in the pathway for synthesizing leucine or in two different genes in that pathway? Explain. b. Write the genotype of the two strains according to your model. c. What progeny and in what proportions would you predict from crossing the two auxotrophic mutants? (Assume independent assortment.)

After irradiating wild-type cells of Neurospora (a haploid fungus), a geneticist finds two leucine-requiring auxotrophic mutants. He combines the two mutants in a heterokaryon and discovers that the heterokaryon is prototrophic.
a. Were the mutations in the two auxotrophs in the same gene in the pathway for synthesizing leucine or in two different genes in that pathway? Explain.
b. Write the genotype of the two strains according to your model.
c. What progeny and in what proportions would you predict from crossing the two auxotrophic mutants? (Assume independent assortment.)

Key Concepts

Complementation Analysis

This technique is used to determine whether different mutations that produce a similar phenotype are in the same gene or in different genes. When two mutants are combined and the wild-type phenotype is restored, it indicates that each mutant provides the gene product that the other is deficient in, implying that the mutations are in different genes.

Heterokaryosis

Heterokaryons are cells or organisms, particularly in fungi, that contain nuclei with different genetic makeups. This state allows for the sharing of gene products among nuclei, which can lead to complementation of defects present in individual nuclei. It is a vital concept for genetic studies in organisms where cells can harbor multiple, genetically distinct nuclei.

Auxotrophy

Auxotrophy refers to the condition in which an organism is unable to synthesize a specific compound that is essential for its growth due to a mutation. Mutants exhibiting auxotrophy require supplementation of that compound in their growth medium. This phenotype is commonly used in genetic experiments to map gene function and to perform complementation tests.

Independent Assortment

Independent assortment is a fundamental principle of genetics stating that alleles of different genes segregate into gametes independently of one another during meiosis. This concept is key for predicting the distribution of genotypes and phenotypes in the progeny resulting from a genetic cross, especially under the assumption that the genes are located on different chromosomes.

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