1 (a) Mendelian and non-Mendelian traits. (10M)

Introduction

The study of inheritance is central to biological anthropology, as it explains how traits are transmitted across generations. Gregor Johann Mendel (1865), through his experiments on Pisum sativum (pea plant), laid down the Law of Segregation and Law of Independent Assortment, which formed the basis of Mendelian inheritance. Later, the rediscovery of his work in 1900 by Hugo de Vries, Carl Correns, and Erich von Tschermak established genetics as a science.

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1. 1 Mendelian Traits

   Traits inherited according to Mendel’s laws.

   • Discrete Expression – Mendel (1865) demonstrated monogenic inheritance where traits appear in predictable ratios (3:1, 9:3:3:1).
   • Sickle Cell Anemia – First described by James Herrick (1910); Linus Pauling (1949, “Sickle Cell Anemia, a Molecular Disease”) identified its molecular basis. J.B.S. Haldane (1949) showed its role in balanced polymorphism, explaining resistance to malaria in endemic regions.
   • Blood Group Systems – Karl Landsteiner (1901) discovered the ABO system, following codominant inheritance. Later, Landsteiner and Wiener (1940) discovered the Rh factor, demonstrating Mendelian dominant–recessive transmission.
   • Anthropological Studies – Earnest Hooton (1937) used Mendelian traits like ear lobe attachment in racial classification studies, linking them to human variation.
2. 2 Non-Mendelian Traits

   Inheritance patterns that do not follow Mendel’s ratios.

   • Polygenic Inheritance – Ronald A. Fisher (1918) integrated Mendelian principles with biometrics, showing that multiple genes contribute to continuous variation.
   • Skin Colour – Explained by Charles Davenport (1913, Heredity in Relation to Eugenics) and refined by Hulse (1962) as a polygenic trait influenced by both genes and environment, studied in anthropology as an adaptation to UV radiation.
   • Codominance – ABO blood group (Landsteiner, 1901) where A and B alleles are both expressed in AB phenotype.
   • Sickle Cell Trait – Studied by E.A. Beet (1949) and A.C. Allison (1954), demonstrating codominance: heterozygotes express both normal and abnormal hemoglobin.
   • Pleiotropy – Antoine-Bernard Marfan (1896) described Marfan syndrome, where one gene affects multiple systems (skeletal, cardiovascular, ocular).
   • Mitochondrial Inheritance – Douglas C. Wallace (1980s) demonstrated maternal transmission of mitochondrial DNA, widely used in anthropological genetics for studying human migrations and evolutionary history.
   • Epistasis – Term introduced by William Bateson (1909). Example: Bombay Blood Group, discovered in Mumbai by Bhende (1952), where the H-gene deficiency masks ABO expression; significant in Indian anthropological studies.
3. 3 Contemporary studies:
   • Susan Strome, N. Bhalla, R. Kamakaka, Upasna Sharma, and William Sullivan in their work “Clarifying Mendelian vs non-Mendelian inheritance” (2024) critically examined misconceptions about inheritance patterns. They argued that traits such as incomplete dominance, codominance, and sex-linked inheritance often mislabeled as “non-Mendelian” still obey Mendel’s laws of segregation and independent assortment. The authors highlighted that these cases only deviate from the expected phenotypic ratios, not the fundamental rules, and urged educators and healthcare professionals to correct misleading resources to improve public understanding of genetics.
   • Aruna Kawadkar, Swati Koushik, Sandhya Dhabe, and Trupti Khedka in their study “Inheritance Pattern and Association Studies of Some Human Mendelian Traits among Different Communities from Nagpur, India” (2022) investigated traits such as earlobe attachment, tongue rolling, widow’s peak, Morton’s toe, hitchhiker’s thumb, and eye/hair color across several Indian communities. Using descriptive, interview, and observational methods, they documented how these classic Mendelian and non-Mendelian traits vary in frequency between groups. Their research provided anthropological insight into genetic diversity and morphogenetic patterns shaping human populations.
   • C. Bonilla, Guadalupe Herrera, and M. Sans in their paper “What can Mendelian randomization contribute to biological anthropology?” (2023) introduced Mendelian randomization (MR) as a methodological innovation for anthropological research. They showed how MR, which uses genetic variants as instrumental variables, can strengthen causal inference in areas such as environmental adaptation, nutrition, and life history theory. While acknowledging limitations, they emphasized MR as a powerful complement to traditional observational approaches in anthropology
4. 4 Conclusion:

   While Mendelian traits highlight simple one gene–one character inheritance, non Mendelian traits reflect the complexity of human genetics, showing how multiple factors interact. Together, they form the foundation of human genetics and physical anthropology, aiding in understanding both normal variation and disease inheritance.