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Sickle-cell anemia is caused by a single base substitution in the β-globin gene, leading to the formation of abnormal hemoglobin.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Sickle-cell anemia is caused by a single base substitution in the β-globin gene, leading to the replacement of glutamic acid with valine.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Mendel's Laws - Dominance Segregation Independent Assortment
Heterozygote advantage reflects key principle in quiz on natural selection, where evolutionary mechanisms shape genetic variation and adaptation. In this context, Heterozygote advantage aligns with experimental and theoretical evidence from population genetics, behavioral ecology and molecular phylogeny. Textbooks like Campbell Biology, Futuyma Evolution and Hartl Principles illustrate supporting data. Understanding why Heterozygote advantage fits helps integrate natural selection, environment.
Ref: Futuyma, Evolution, 4th ed., Chapter 11: Natural Selection.
Sickle cell allele causes severe hemolytic disease in homozygous recessive state but confers malaria resistance in heterozygous condition in regions endemic for Plasmodium falciparum. Heterozygotes survive better than both AA individuals susceptible to malaria and SS patients with severe anemia, exemplifying overdominance with highest fitness in heterozygote. This balancing selection maintains S allele at frequency far higher than mutation alone would predict, despite strong purifying selection against SS. Heterozygote advantage therefore explains persistence of otherwise deleterious allele in African, Mediterranean, and Indian populations historically exposed.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 20: Hemoglobin Polymorphism and Balancing Selection
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