Practice question

Early Drosophila genetics by Thomas Morgan identified yellow body y and white eye w mutations showing distinctive criss-cross inheritance pattern. Reciprocal crosses produced sex-biased progeny where sons frequently resembled mother for X-linked traits because male receives his single X from maternal parent. Daughters received X from both parents, masking recessive trait when heterozygous. Repeated observation established genes y and w reside on X chromosome, not autosome, Y, or mitochondrion. These markers became foundational for constructing first genetic map and demonstrating chromosomal theory of inheritance.