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A carrier female for hemophilia has the genotype XhX, where one X chromosome carries the recessive hemophilia allele.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Chromosomal Theory Linkage Recombination Gene Mapping
When both body color and eye color genes reside on X chromosome, inheritance pattern becomes sex-linked dihybrid with linkage on same chromosome. Females have two X chromosomes that can recombine during meiosis, generating recombinant X gametes; males have single X transmitted intact to daughters. Consequently joint segregation shows association with sex and parental origin, unlike autosomal dihybrid where both sexes identical. Mapping distance between X-linked genes estimated from recombinant frequency in female progeny only. This pattern excludes autosomal dihybrid, Y-linked, or cytoplasmic inheritance models.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Sex-Linked Dihybrid Linkage
X-linked genes reside on X chromosome where dosage differs between XX females and XY males. In Drosophila, sons receive X from mother and Y from father, daughters receive X from both. Consequently swapping mutant and wild type between sexes changes which sex inherits mutant X, altering progeny phenotypes. For X-linked recessive white eye, one reciprocal direction yields white-eyed sons and red-eyed daughters, opposite reciprocal yields different distribution. Such non-equivalence between reciprocals contrasts with autosomal crosses showing identical outcomes and signals X-chromosome location and hemizygous male expression.
Ref: Morgan et al., Mechanism of Mendelian Heredity; Griffiths Chapter 4: Reciprocal Differences in X-Linkage
