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Related Concept Videos

Principles of Pharmacogenetics: Types of Genetic Variants01:27

Principles of Pharmacogenetics: Types of Genetic Variants

The human genome is over 99.9% identical between individuals, yet genetic differences exist at millions of bases. The human genome contains approximately 3 million variant positions per individual, many of which are heterozygous, contributing to genetic diversity and individual traits. Genetic variations include single-nucleotide polymorphisms (SNPs), insertions, deletions, and copy number variations (CNVs).SNPs, the most common variation, involve single-base changes in DNA. These can be...
Comparing Copy Number Variations and SNPs02:26

Comparing Copy Number Variations and SNPs

Sequencing of the human genome has opened up several best-kept secrets of the genome. Scientists have identified thousands of genome variations that exist within a population. These variations can be a single nucleotide or a larger chromosomal variation.
Copy number variations or CNVs are the structural variations that cover more than 1kb of DNA sequence. The single nucleotide polymorphism (SNP), on the other hand, is a single nucleotide change or a point mutation that is found in more than 1%...
Genetic Variation01:25

Genetic Variation

Genetic variation is the diversity in DNA sequences found among individuals of the same species. This diversity is crucial for a species' survival because it helps organisms adapt to environmental changes. Genetic variation begins with fertilization, where an egg and sperm cell merge. Each of these cells carries 23 chromosomes, up to 46 in the fertilized egg. Chromosomes are long DNA strands that contain genes, the basic units of heredity.
Genes exist in different versions called alleles, which...
Single Nucleotide Polymorphisms-SNPs01:05

Single Nucleotide Polymorphisms-SNPs

A single nucleotide polymorphism or SNP is a single nucleotide variation at a specific genomic position in a large population. It is the most prevalent type of sequence variation found in the human genome. Point mutations that occur in more than 1% of the population qualify as SNPs. These are present once every 1000 nucleotides on an average in the human genome. Replacement of a purine with another purine (A/G) or a pyrimidine with another pyrimidine (C/T) is known as a transition. In contrast,...
Incomplete Dominance01:43

Incomplete Dominance

Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.
Histone Variants at the Centromere02:30

Histone Variants at the Centromere

Histone variants are the histone proteins with structural and sequence variations. These variants may be regarded as “mutant” forms that replace their canonical histone counterparts in the nucleosomes. Specific post-translational modifications on the histone variants enable further chromatin complexity and regulate tissue-specific gene expression. The most common histone variants are from histone H2A, H2B, and linker histone H1 families. However, several variants of histone H3 variants are also...

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Related Experiment Video

Updated: Jun 15, 2026

Detection of Rare Genomic Variants from Pooled Sequencing Using SPLINTER
14:06

Detection of Rare Genomic Variants from Pooled Sequencing Using SPLINTER

Published on: June 23, 2012

A remark on rare variants.

Konrad Oexle1

  • 1Institute of Human Genetics, Klinikum rechts der Isar, Technische Universität München, Munich, Germany. oexle@humangenetik.med.tum.de

Journal of Human Genetics
|March 6, 2010
PubMed
Summary

Moderately rare genetic variants significantly impact disease risk. Association tests like the transmission disequilibrium test (TDT) can detect these, but require substantial sample sizes for variants with lower frequency or effect size.

Area of Science:

  • Genetics
  • Epidemiology
  • Biostatistics

Background:

  • Common diseases have complex genetic underpinnings.
  • Bodmer and Bonilla proposed that moderately rare variants contribute significantly to population attributable risk (PAR).
  • Understanding genetic architecture is crucial for epidemiological study design.

Purpose of the Study:

  • To reconstruct and analyze the power of linkage and association tests for identifying disease-associated variants.
  • To compare the sensitivity of affected sib-pair linkage (ASP) and transmission disequilibrium association (TDT) tests, especially at low allele frequencies.
  • To determine minimal sample sizes for detecting disease-contributing variants under a specific genetic model.

Main Methods:

  • Reconstruction of Bodmer and Bonilla's deliberation on genetic variants and PAR.

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In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila
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In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

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Last Updated: Jun 15, 2026

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  • Comparison of ASP and TDT power, with approximations for low allele frequencies.
  • Analysis of a disease model based on Kimura's infinite sites model, relating selection coefficient to effect size.
  • Application of the TDT to the disease model to derive minimal detectable sample sizes.

    • Main Results:

    • The linkage test (ASP) is more sensitive than the association test (TDT) to decreased variant frequency or effect size.
    • For a specific disease model, the TDT requires substantial sample sizes to detect most contributing variants.
    • Moderately strong variants at approximately 1% frequency necessitate a minimum sample size for detection.

    Conclusions:

    • Genetic architecture significantly influences the choice and power of epidemiological methods.
    • While many variants remain undetectable, moderately strong variants at low frequencies can be identified with appropriate sample sizes.
    • The study provides insights into the sample size requirements for genetic association studies of common diseases.