Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed. Phenotype Male Offspring y + ct 9 + w + 6 y w ct 90 + + + 95 + + ct 424 y w + 376 y + + 0 + w ct 0 Diagram the genotypes of the F₁ parents.

Key Concepts

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. In Drosophila, males have one X and one Y chromosome, while females have two X chromosomes. This means that recessive traits linked to the X chromosome are more likely to be expressed in males, as they have only one copy of the X chromosome. Understanding this concept is crucial for analyzing the inheritance patterns of traits in the given cross.

Phenotypic Ratios

Phenotypic ratios describe the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this case, the phenotypes of the male offspring are recorded, allowing for the determination of how traits segregate and assort. Analyzing these ratios helps in understanding the genetic linkage and the dominance of traits, which is essential for constructing a genetic map.

Genetic Mapping

Genetic mapping is the process of determining the relative positions of genes on a chromosome based on the frequency of recombination between them. In this scenario, the data from the F₂ progeny allows for the construction of a genetic map that illustrates the distances between the genes yellow, white, and cut. This mapping is vital for predicting inheritance patterns and understanding the genetic architecture of the traits studied.