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Related Concept Videos

Comparing Copy Number Variations and SNPs02:26

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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%...
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In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).
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When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.
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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,...
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Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
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Diploid organisms inherit genetic material through chromosomes from both parents. Copies of the same gene are known as alleles. In most cases, both alleles are simultaneously expressed and allow various cellular processes to function optimally. If one of the alleles is missing or mutated, the expression of the other allele can compensate; however, this is not true for all genes.
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Related Experiment Video

Updated: Aug 14, 2025

Generation of Genomic Deletions in Mammalian Cell Lines via CRISPR/Cas9
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Balancing selection on genomic deletion polymorphisms in humans.

Alber Aqil1, Leo Speidel2,3, Pavlos Pavlidis4

  • 1Department of Biological Sciences, University at Buffalo, Buffalo, United States.

Elife
|January 10, 2023
PubMed
Summary
This summary is machine-generated.

Ancient deletions, or genomic variations predating the human-Neanderthal split, persist due to balancing selection. These ancient polymorphisms are linked to metabolism and immunity, offering insights into human evolution.

Keywords:
DenisovansNeanderthalscopy number variationevolutionevolutionary biologygeneticsgenomicshumanstructural variation

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Area of Science:

  • Evolutionary biology
  • Human genetics
  • Population genetics

Background:

  • Genomic variation, particularly deletions, can persist for long evolutionary periods.
  • Balancing selection is a proposed mechanism for the long-term maintenance of genetic polymorphisms.
  • Understanding the evolutionary forces shaping ancient deletions is crucial for human genomics.

Purpose of the Study:

  • To investigate the evolutionary mechanisms maintaining ancient deletion polymorphisms in the human lineage.
  • To determine the role of balancing selection in the persistence of these ancient deletions.
  • To identify functional implications and associated traits of ancient deletions.

Main Methods:

  • Analysis of ancient polymorphisms predating the human-Neanderthal split.
  • Application of a quantitative measure for balancing selection.
  • Examination of signatures of selection, including overdominance.
  • Association analysis with genome-wide association studies (GWAS) data.
  • Enrichment analysis for specific biological traits.

Main Results:

  • An excess of ancient polymorphisms was observed, not explainable by neutral evolution.
  • Balancing selection was identified as the primary driver for the excess of ancient deletions.
  • Overdominance was found to be a rare mode of balancing selection for these deletions.
  • Ancient deletions are enriched for exonic variants with genome-wide association studies (GWAS) associations.
  • Significant enrichment for metabolism and immunity-related traits was found in ancient deletions.
  • Deletions were found to be, on average, more deleterious than single nucleotide variants.

Conclusions:

  • Balancing selection, likely involving complex spatio-temporal variations, maintains ancient deletions.
  • Ancient deletions harbor biologically relevant variants influencing metabolism and immunity.
  • A significant portion of human genetic variation, including deletions, has ancient origins and has been maintained over long evolutionary timescales.