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Color blindness follows an X-linked recessive inheritance pattern, primarily affecting males.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Polygenic Inheritance Pleiotropy and Quantitative Inheritance
Thalassemia is inherited in an autosomal recessive manner, requiring two mutated alleles for the disease to manifest.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
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
Reciprocal crosses interchange which sex provides which parental phenotype, e.g., female phenotype A x male phenotype B versus female B x male A. For autosomal inheritance, both sexes carry two copies and transmit alleles equally through meiosis, independent of sex. Consequently F1 and F2 phenotypic distributions remain identical regardless of cross direction. Identical reciprocal results therefore exclude sex-linked inheritance where males inherit X from mother and sex-limited or cytoplasmic patterns involving mitochondrial DNA. Uniformity supports autosomal location with equal biparental transmission.
Ref: Pierce, Genetics: A Conceptual Approach, 7th ed., Chapter 4: Reciprocal Crosses as Test for Autosomal Inheritance
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