Define genetic polymorphism. Give details of its types with suitable examples.

Defining Genetic Polymorphism

Genetic polymorphism, at its core, refers to the existence of two or more alleles for a particular gene or DNA sequence in a population, with a frequency of at least 1% for the less common allele. This threshold of 1% distinguishes polymorphism from a rare mutation. A mutation, by definition, is a change in the DNA sequence that is present at a much lower frequency, often below 1%. Genetic polymorphisms are heritable and contribute significantly to the phenotypic variation observed within a population.

Types of Genetic Polymorphism

Genetic polymorphism can be broadly categorized into allelic, discrete, and continuous polymorphisms. Each type exhibits different characteristics and patterns of inheritance.

Allelic Polymorphism

Allelic polymorphism involves variations in a single nucleotide (point mutations) or small insertions/deletions within a gene. These changes can lead to altered protein structure or function. A classic example is the sickle cell allele (HbS) in humans.

• Example: Sickle Cell Anemia The normal hemoglobin allele (HbA) and the sickle cell allele (HbS) demonstrate allelic polymorphism. Individuals can have genotypes AA, AS, or SS. The HbS allele provides resistance to malaria, showcasing an adaptive advantage in certain environments.
• Definition: Allele An alternative form of a gene at a specific locus.

Discrete Polymorphism

Discrete polymorphisms involve variations that result in distinct, easily observable phenotypes. These often involve differences in the number of repeats of a DNA sequence or the presence or absence of a gene. These are often categorized as structural variants.

• Example: Blood Groups The ABO blood group system is a prime example of discrete polymorphism. The A, B, and O alleles determine the presence or absence of specific antigens on red blood cells.
• Example: Lactase Persistence The ability to digest lactose into adulthood (lactase persistence) is a discrete trait controlled by a single nucleotide polymorphism (SNP) near the LCT gene. This trait is prevalent in populations with a history of dairy farming.

Continuous Polymorphism

Continuous polymorphisms are quantitative traits that show a continuous range of variation within a population. These are typically influenced by multiple genes (polygenic inheritance) and environmental factors. Examples include height, skin color, and body weight.

• Example: Skin Pigmentation Skin pigmentation is a classic example of a continuously varying trait. It’s influenced by multiple genes (e.g., MC1R, OCA2) and environmental factors like sun exposure.
• Statistic: According to a 2018 study in *Nature*, skin pigmentation is influenced by over 100 genetic loci.

Type of Polymorphism	Description	Example	Inheritance Pattern
Allelic	Variations in a single nucleotide or small insertion/deletion.	Sickle Cell Anemia (HbS vs. HbA)	Mendelian
Discrete	Distinct, easily observable phenotypes.	ABO Blood Groups	Co-dominant/Incomplete Dominance
Continuous	Quantitative traits with a continuous range of variation.	Skin Pigmentation	Polygenic, influenced by environment

Significance in Anthropology and Genetics

Genetic polymorphism is crucial for understanding human evolutionary history, population structure, and disease susceptibility. By analyzing the distribution of polymorphisms across different populations, anthropologists can reconstruct migration patterns, identify relationships between groups, and gain insights into adaptation to different environments.

• Case Study: Y-chromosome DNA analysis Y-chromosome DNA analysis, which tracks paternal lineages, has been used to trace the migration of human populations across continents, revealing patterns of dispersal and genetic relatedness.
• FAQ: How does genetic polymorphism contribute to disease susceptibility? Many diseases are influenced by genetic polymorphisms. For example, variations in genes involved in immune response can affect an individual's susceptibility to infectious diseases.

Modern Applications & Technology

Advancements in high-throughput sequencing technologies (e.g., genome-wide association studies – GWAS) have facilitated the identification of numerous polymorphisms and their association with various traits and diseases. Single Nucleotide Polymorphisms (SNPs) are now routinely used in genetic research and personalized medicine.

• Scheme: National Biobank Mission The Indian National Biobank Mission aims to collect biological samples and associated health data from diverse populations to facilitate genetic research and improve healthcare.
• Statistic: GWAS studies have identified over 10,000 genetic loci associated with human diseases (as of 2023 – Knowledge Cutoff).

In conclusion, genetic polymorphism is a cornerstone of genetic diversity and a key driver of evolutionary change. Understanding the various types of polymorphism, from allelic variations to continuous traits, is essential for anthropologists, geneticists, and healthcare professionals. The continued advancement of genomic technologies promises to further unravel the complexities of genetic polymorphism and its impact on human health and evolution, allowing for more targeted interventions and a deeper understanding of our shared ancestry.