Genetic polymorphism is a cornerstone of human biological diversity, reflecting the variations in genetic makeup among individuals and populations. It refers to the presence of multiple alleles for a particular gene or DNA sequence within a population, with a frequency of at least 1% for a variant to be considered a polymorphism. The Human Genome Project (completed in 2003) revolutionized our understanding of genetic variation, revealing millions of polymorphisms across the human genome. These variations contribute to phenotypic differences, influence susceptibility to diseases, and provide insights into human evolutionary history and adaptation. The study of these polymorphisms is critical for understanding human biological diversity and its implications. Defining Genetic Polymorphism A genetic polymorphism, derived from Greek 'poly' (many) and 'morph' (form), signifies the existence of multiple forms of a gene or DNA sequence within a population. Unlike mutations, which are typically rare and often deleterious, polymorphisms are relatively common and often neutral or even beneficial, contributing to the genetic diversity that drives evolution. The 1% frequency threshold is arbitrary but distinguishes polymorphisms from rare mutations. Types of Genetic Polymorphisms Genetic polymorphisms manifest in various forms, each with distinct characteristics and analytical approaches: Single Nucleotide Polymorphisms (SNPs): These are the most common type, representing variations at a single nucleotide base (A, T, C, or G). SNPs are abundant throughout the genome and serve as markers for genetic variation. Microsatellites (Short Tandem Repeats - STRs): These are short, repetitive DNA sequences (e.g., CACACACACA) that vary in the number of repeats. STRs are highly polymorphic and are widely used in forensic science and population genetics. Insertions/Deletions (Indels): These involve the presence or absence of short DNA segments. Indels can range in size from a few base pairs to hundreds of base pairs. Copy Number Variations (CNVs): These involve differences in the number of copies of larger DNA segments, ranging from a few kilobases to several megabases. Significance in Anthropology Genetic polymorphisms play a crucial role in anthropological studies: Population Genetics: Polymorphisms are used to reconstruct human migration patterns, determine genetic relationships between populations, and assess genetic drift and gene flow. For example, studies of Y-chromosome and mitochondrial DNA polymorphisms have shed light on the Out-of-Africa theory of human origins. Human Adaptation: Certain polymorphisms are associated with adaptation to specific environmental conditions. The ability to digest lactose in adulthood, for instance, is a genetic polymorphism that arose independently in several populations with a history of dairy farming. Disease Susceptibility: Polymorphisms can influence an individual’s susceptibility to various diseases. For example, variations in the CCR5 gene provide resistance to HIV infection. Forensic Anthropology: STRs are routinely used in DNA fingerprinting for identification purposes and in tracing ancestry. Analytical Techniques Several techniques are employed to analyze genetic polymorphisms: PCR (Polymerase Chain Reaction): Used to amplify specific DNA regions for analysis. DNA Sequencing: Determines the precise order of nucleotides in a DNA fragment. Microarrays (SNP Chips): Allow for the simultaneous genotyping of hundreds of thousands or even millions of SNPs. Next-Generation Sequencing (NGS): Enables high-throughput sequencing of entire genomes or exomes, revealing a vast amount of genetic variation. Case Study: Lactase Persistence The evolution of lactase persistence, the ability to digest lactose into adulthood, provides a compelling example of how genetic polymorphisms adapt to cultural changes. In populations with a long history of dairy farming (e.g., Northern Europeans, East African pastoralists), a mutation arose that allows the lactase gene to remain active beyond childhood. This mutation conferred a selective advantage, leading to its increased frequency in these populations. Type of Polymorphism Characteristics SNPs Single nucleotide variation, most common STRs Short repetitive sequences, highly variable CNVs Variations in copy number of DNA segments Genetic polymorphism is a fundamental aspect of human biological diversity, driving adaptation, influencing disease susceptibility, and informing our understanding of human evolutionary history. The advent of high-throughput sequencing technologies has greatly accelerated the discovery and characterization of genetic polymorphisms, opening new avenues for anthropological research. Future research will focus on understanding the functional consequences of these variations and their role in shaping human health and behavior, furthering our comprehension of what it means to be human.

Genetic Polymorphism: Definition & Significance | UPSC Mains ANTHROPOLOGY-PAPER-I 2011

Genetic polymorphism

How to Approach

This question requires a clear understanding of genetic polymorphism and its implications in anthropology. The approach should be to first define genetic polymorphism and its significance. Then, discuss different types of polymorphisms (e.g., SNPs, microsatellites) and their role in human variation, adaptation, and disease susceptibility. Finally, briefly touch upon the analytical techniques used to study genetic polymorphisms. Structure the answer with clear headings and subheadings for better readability. Focus on anthropological relevance.

Genetic polymorphism is a cornerstone of human biological diversity, reflecting the variations in genetic makeup among individuals and populations. It refers to the presence of multiple alleles for a particular gene or DNA sequence within a population, with a frequency of at least 1% for a variant to be considered a polymorphism. The Human Genome Project (completed in 2003) revolutionized our understanding of genetic variation, revealing millions of polymorphisms across the human genome. These variations contribute to phenotypic differences, influence susceptibility to diseases, and provide insights into human evolutionary history and adaptation. The study of these polymorphisms is critical for understanding human biological diversity and its implications.

Defining Genetic Polymorphism

A genetic polymorphism, derived from Greek 'poly' (many) and 'morph' (form), signifies the existence of multiple forms of a gene or DNA sequence within a population. Unlike mutations, which are typically rare and often deleterious, polymorphisms are relatively common and often neutral or even beneficial, contributing to the genetic diversity that drives evolution. The 1% frequency threshold is arbitrary but distinguishes polymorphisms from rare mutations.

Types of Genetic Polymorphisms

Genetic polymorphisms manifest in various forms, each with distinct characteristics and analytical approaches:

Single Nucleotide Polymorphisms (SNPs): These are the most common type, representing variations at a single nucleotide base (A, T, C, or G). SNPs are abundant throughout the genome and serve as markers for genetic variation.
Microsatellites (Short Tandem Repeats - STRs): These are short, repetitive DNA sequences (e.g., CACACACACA) that vary in the number of repeats. STRs are highly polymorphic and are widely used in forensic science and population genetics.
Insertions/Deletions (Indels): These involve the presence or absence of short DNA segments. Indels can range in size from a few base pairs to hundreds of base pairs.
Copy Number Variations (CNVs): These involve differences in the number of copies of larger DNA segments, ranging from a few kilobases to several megabases.

Significance in Anthropology

Genetic polymorphisms play a crucial role in anthropological studies:

Population Genetics: Polymorphisms are used to reconstruct human migration patterns, determine genetic relationships between populations, and assess genetic drift and gene flow. For example, studies of Y-chromosome and mitochondrial DNA polymorphisms have shed light on the Out-of-Africa theory of human origins.
Human Adaptation: Certain polymorphisms are associated with adaptation to specific environmental conditions. The ability to digest lactose in adulthood, for instance, is a genetic polymorphism that arose independently in several populations with a history of dairy farming.
Disease Susceptibility: Polymorphisms can influence an individual’s susceptibility to various diseases. For example, variations in the CCR5 gene provide resistance to HIV infection.
Forensic Anthropology: STRs are routinely used in DNA fingerprinting for identification purposes and in tracing ancestry.

Analytical Techniques

Several techniques are employed to analyze genetic polymorphisms:

PCR (Polymerase Chain Reaction): Used to amplify specific DNA regions for analysis.
DNA Sequencing: Determines the precise order of nucleotides in a DNA fragment.
Microarrays (SNP Chips): Allow for the simultaneous genotyping of hundreds of thousands or even millions of SNPs.
Next-Generation Sequencing (NGS): Enables high-throughput sequencing of entire genomes or exomes, revealing a vast amount of genetic variation.

Case Study: Lactase Persistence

The evolution of lactase persistence, the ability to digest lactose into adulthood, provides a compelling example of how genetic polymorphisms adapt to cultural changes. In populations with a long history of dairy farming (e.g., Northern Europeans, East African pastoralists), a mutation arose that allows the lactase gene to remain active beyond childhood. This mutation conferred a selective advantage, leading to its increased frequency in these populations.

Type of Polymorphism	Characteristics
SNPs	Single nucleotide variation, most common
STRs	Short repetitive sequences, highly variable
CNVs	Variations in copy number of DNA segments

Additional Resources

Key Definitions

Allele

One of two or more alternative forms of a gene at a given locus.

Haplotype

A set of DNA variations (SNPs, microsatellites, etc.) that tend to be inherited together from a single parent.

Key Statistics

The average number of SNPs per human genome is estimated to be around 3 million.

Source: National Human Genome Research Institute

Approximately 99.9% of human DNA is identical between individuals; the remaining 0.1% accounts for genetic polymorphisms.

Source: Human Genome Project

Examples

Sickle Cell Anemia

A classic example of a genetic polymorphism, the sickle cell allele (HbS) provides resistance to malaria but causes sickle cell anemia in homozygous individuals.

Frequently Asked Questions

▶What is the difference between a mutation and a polymorphism?

Mutations are typically rare, often deleterious, and arise spontaneously. Polymorphisms are relatively common, often neutral or beneficial, and are already present in the population at a significant frequency.