Four eye-color mutants in Drosophila—apricot, brown, carnation, and purple—are inherited as recessive traits. Red is the dominant wild-type color of fruit-fly eyes. Eight crosses (A through H) are made between parents from pure-breeding lines.

Which of these eye-color mutants are X-linked recessive and which are autosomal recessive? Explain how you distinguish X-linked from autosomal heredity. <>

Key Concepts

X-linked vs. Autosomal Inheritance

X-linked inheritance refers to traits associated with genes located on the X chromosome, while autosomal inheritance involves genes on non-sex chromosomes. In X-linked recessive traits, males (XY) are more likely to express the trait because they have only one X chromosome, whereas females (XX) can be carriers without showing the trait if they have one dominant allele.

Recessive Traits

Recessive traits require two copies of the recessive allele for expression in autosomal inheritance. In the case of X-linked traits, males only need one copy of the recessive allele on their single X chromosome to express the trait, while females need two copies on both X chromosomes. This difference is crucial for determining the inheritance pattern of the eye-color mutants.

Pure-breeding Lines

Pure-breeding lines consist of organisms that consistently produce offspring with the same phenotype when self-fertilized or crossed with each other. In the context of the Drosophila eye-color mutants, pure-breeding lines help establish the genetic basis of the traits, allowing researchers to determine whether the mutants are X-linked or autosomal by analyzing the offspring's phenotypes in controlled crosses.