Final answer:
Heritable variation in stalk-eyed flies suggests that these traits can be passed on genetically and may be subject to natural selection. In fruit flies, this principle is observed with inheritance patterns of dominant and recessive traits, and has parallels in human genetics with X-linked conditions.
Step-by-step explanation:
When the student asks about stalk-eyed flies and heritable variation, they're likely addressing the concept of genetic inheritance and natural selection in Biology. If variation within a trait, such as the eye stalk length in stalk-eyed flies, is heritable, it means that these traits can be passed down from parent to offspring through genetic material. If these heritable traits also confer some advantage or disadvantage in terms of survival or reproduction (fitness), they can be acted upon by natural selection. Over time, this may lead to an increase or decrease in the frequency of the trait within the population.
In the details provided, we see an application of these principles in fruit fly (Drosophila melanogaster) genetics. The cross of a true-breeding wild-type male fly with a true-breeding female with a black body and cinnabar eyes results in all F1 progeny displaying the wild-type phenotype. This suggests that the wild-type traits are dominant over the mutant traits. The application of these findings in fruit fly genetics can also extend to human genetics, where certain conditions, like some forms of color blindness or hemophilia, are inherited through X-linked alleles. Females may be carriers without showing any phenotypic effects, but can pass the trait to their offspring.