Sex-linked Traits of Drosophila melanogaster (Fruit fly): Eye Color

Drosophila melanogaster also known as fruit fly is usually found around fruits that are not ripe or have become rotten. It has proved to be very useful in the study of genetics and inheritance of traits for several decades. In the 1900's, T.H. Morgan discovered sex-linkage and recombination using Drosophila in his studies. Ever since then, biologists have used fruit flies when carrying out genetic research and studies.

Other reasons they have been used by biologists are their small size, sexually dimorphic-nature, short generation time, easy-process to get them asleep, inexpensive and easy-to-access culture equipment among others.

Some traits that drosophila expresses are x-linked and among these traits include: wing length, wing shape, eye color, bar eye and body color. These traits are usually expressed in offspring depending on the sex of the parent. Usually, drosophila males possess the XY-chromosome pair and the females, the XX-chromosome pair. With this, the different eye colors of fruit flies were studied. 

The wild-type fruit fly has its eye colored red and this trait is dominant to the fruit fly with a white eye color. It is important to note that eye color is found on the X-chromosome alone. Now, because of the hemizygous nature of males where they have just one allele for X-linked traits, a reciprocal cross will not produce offspring in the same genotypic and phenotypic ratios.

Consequently, the idea of dominance and recessiveness doesn't exactly apply to males in this case because of their hemizygous nature that makes then have just one copy of the gene on their X-chromosome and none on the Y-chromosome. Females on the other hand are in contrast with males because they have two copies of the trait on each of their X-chromosomes.

Sources

https://depts.washington.edu/cberglab/wordpress/outreach/an-introduction-to-fruit-flies/

https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/12%3A_Mendel's_Experiments_and_Heredity/12.02%3A__Patterns_of_Inheritance/12.2E%3A_Sex-Linked_Traits#:~:text=1%3A%20Eye%20color%20in%20Drosophila,dominant%20to%20white%20eye%20color.