A researcher studying fruit flies knows that fruit fly eye color is controlled by a single gene. The researcher notices a new mutation in one of the fruit fly lines. How could the researcher determine whether this mutation is caused by a change in the number of chromosomes or by a change within the single gene?

Question

BlackTom AI · Accepted Answer

The scenario presents a single-gene trait (eye color) in fruit flies and a new mutation. The student must weigh how to tell if the mutation affects chromosome number (aneuploidy, etc.) versus a change within the single gene.
Option 1: 'By measuring eye size to see if the new mutation caused any other changes to the structure of the fruit fly’s eye.' This approach looks for pleiotropy or ancillary phenotypic effects but does not specifically test chromosome number or gene-level changes. Eye size could be influenced by many factors and would not reliably distinguish between chromosomal alterations and gene-level mutations.
Option 2: 'By analyzing the karyotype of a mutated fly compared to a non-mutated fly to determine if there are extra or missing chromosomes' This directly targets chromosome number. Karyotyping reveals whole-chromosome gains or losses, which would indicate aneuploidy, whereas a single-gene mutation that does not alter chromosome count would not change the karyotype. This is the appropriate method to differentiate between chromosomal changes and a gene-level change.
Option 3: 'By exposing the mutated fly to different toxins and to see if more mutations can be introduced into the fly line' This is an mutagenesis approach to generate additional mutations, not a diagnostic test to determine the cause of the existing mutation. It would not reveal whether the original mutation involved chromosome number or a gene alteration.
Option 4: 'By continuing to breed the mutated fly with a non-mutated fly and tracking the number of offspring with the new mutation' This is a classic inheritance-tracking method, useful for studying transmission patterns, but it does not directly assess whether the mutation arises from a chromosomal abnormality or a single-gene change. It would provide information on inheritance, not the molecular basis of the mutation.
In summary, the karyotype analysis (Option 2) is the correct and most direct approach to distinguish between a chromosome-number alteration and a change within the single gene, while the other options either assess unrelated traits, attempt to induce further mutations, or examine inheritance without addressing the underlying chromosomal vs. gene-level origin.

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