What happens during a dominant modifier screen in the fly?

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BlackTom AI · Accepted Answer

In a dominant modifier screen in Drosophila genetics, researchers look for mutations that change the phenotype of an existing sensitised background. 
Option a: 'A phenotype is altered when performed on a sensitised background' correctly reflects the core idea of a dominant modifier screen, where a secondary mutation modifies an already altered or stressed phenotype, revealing interaction with the pathway or process of interest. 
Option b: 'A gene is deleted if it lies in the same pathway as another gene' describes a concept more aligned with epistasis or synthetic lethality, not specifically how a dominant modifier screen is defined. Modifier screens do not automatically imply gene deletion or a constraint about pathway co-location. 
Option c: 'Flies that are heterozygous for a mutation are converted to homozygotes' describes homozygous rescue or balancer/gene conversion schemes, not the aim of modifier screening, which seeks dominant effects on a sensitised background rather than converting zygosity. 
Option d: 'The screen is conducted to identify recessive alleles' is misleading because dominant modifier screens are specifically designed to reveal dominant interactions that modify a phenotype in the presence of another mutation or sensitised state; while recessive alleles can be identified in other types of screens, this option does not capture the defining purpose of a dominant modifier screen. 
Overall, the key misconception to avoid is thinking the screen’s purpose is about deletions, homozygosity changes, or solely recessive discovery; the essential feature is altering a phenotype in a sensitised background through dominant modification.

What happens during a dominant modifier screen in the fly?

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