Name: genome variation in cnvs and snps
Uploaded: 2021-04-07T12:11:59.000Z
Duration: 2 min 26 s
Channel: JoVE

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High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-1

comparing-copy-number-variations-and-snps

Comparing Copy Number Variations and SNPs

Des variations génomiques telles que l’ajout ou la suppression de segments d’ADN sont couramment observées dans une population. Les variations génomiques d’une population peuvent survenir en raison de modifications nucléotidiques uniques dans l’ADN ou de modifications structurelles des chromosomes.
La variation du nombre de copies ou CNV est un terme générique qui définit les variations structurelles impliquant des segments d’ADN de plus de 1 kilo paire de bases.
Si le segment chromosomique impliqué contient un gène, les CNV peuvent augmenter le nombre de copies de ce gène par duplication et insertion ou le diminuer par délétion, ce qui entraîne un génotype nul.
Par conséquent, certaines personnes peuvent avoir deux copies ou même plus d’un gène, ou aucune copie du tout. Par exemple, certaines personnes d’ascendance génétique européenne peuvent porter deux copies du gène du groupe sanguin rhésus, RHD, tandis que d’autres peuvent n’en avoir qu’une et d’autres aucune.  
La CNV peut affecter les phénotypes qui dépendent du nombre de copies de gènes fonctionnels. Dans les régions euro-américaines et asiatiques où les régimes à base d’amidon sont courants, la population présente un nombre de copies plus élevé du gène AMY1, un gène impliqué dans le métabolisme de l’amidon.
Les CNV sont également liés à plusieurs maladies telles que le psoriasis, la maladie de Parkinson et les troubles du comportement comme l’autisme et la schizophrénie.
Alors que les CNV couvrent généralement de grandes variations de séquences d’ADN, les polymorphismes mononucléotidiques ou SNP sont des substitutions aléatoires d’une seule base que l’on trouve dans tout le génome.
De telles substitutions de bases se produisent une fois tous les 1000 nucléotides, mais tous ne sont pas qualifiés de SNP. En général, seule une variation nucléotidique que l’on trouve chez plus de 1 % de la population est appelée SNP.
Les SNP peuvent conférer diverses maladies telles que le diabète ou le cancer. Par exemple, chez les patients atteints d’anémie falciforme, une substitution d’une seule base de l’adénine à la thymine dans un locus spécifique du gène de la bêta-globine provoque des globules rouges en forme de faucille.

<ol>
	<li>Lee, Charles et Stephen W. Scherer. « Le contexte clinique de la variation du nombre de copies dans le génome humain. » Revues d’experts en médecine moléculaire 12 (2010).</li>
	<li>Budowle, Bruce et Angela Van Daal. « Classes SNP médico-légales. » Biotechniques 44, n° 5 (2008) : 603-610.</li>
</ol>

comparaison des variations du nombre de copies et des snp

Le séquençage du génome humain a révélé plusieurs secrets les mieux gardés du génome. Les scientifiques ont identifié des milliers de variations du génome qui existent au sein d’une population. Ces variations peuvent être un seul nucléotide ou une variation chromosomique plus importante.

Les variations du nombre de copies ou CNV sont les variations structurelles qui couvrent plus de 1 Ko de séquence d'ADN. Le polymorphisme nucléotidique unique (SNP), quant à lui, est un changement de nucléotide unique ou une mutation ponctuelle que l'on retrouve chez plus de 1 % de la population. Les CNV et les SNP sont extrêmement précieux dans les études de dépistage génétique et l’analyse de parenté.

Formes de CNV.

Il existe cinq formes de CNV. La première s’appelle une suppression. La perte d'un segment d'ADN peut réduire le nombre de copies d'un gène ou d'un groupe de gènes. La seconde est appelée duplication tandem. Ici, une copie d'un segment chromosomique est insérée dans une région adjacente. La troisième est appelée duplication non contiguë. Ici, un segment chromosomique se duplique et s'insère dans une région chromosomique distante ou dans un chromosome différent. La quatrième forme est appelée CNV multiallélique. Un segment d’ADN se duplique plusieurs fois et aboutit à la formation de plusieurs allèles d’un gène. La cinquième forme est appelée réarrangement complexe. Ici, un segment d’ADN se duplique et s’inverse avant d’être réinséré dans le même chromosome ou dans un autre chromosome.

Polymorphisme nucléotidique unique

Le polymorphisme nucléotidique unique ou SNP est un autre type de variation génomique impliquant des altérations dans une base nucléotidique unique. Les scientifiques ont identifié des milliers de SNP dans le génome humain et ils sont couramment utilisés comme marqueurs génétiques pour les maladies héréditaires et les analyses médico-légales.

En fonction de leur application, les SNP sont divisés en quatre types. Les SNP de test d’identité sont utilisés pour différencier les personnes et les éliminer des liens familiaux. Les SNP informatifs sur la lignée sont des SNP étroitement liés qui aident à identifier les individus manquants dans une analyse familiale. Les SNP informatifs sur l’ascendance aident à établir l’ascendance d’une personne et à la relier à ses caractéristiques phénotypiques. Les SNP informatifs sur le phénotype établissent la probabilité d'hériter d'un phénotype particulier, tel que la couleur de la peau, la couleur des yeux, etc.

Comparaison des variations du nombre de copies et des SNP

Le séquençage du génome humain a révélé plusieurs secrets les mieux gardés du génome. Les scientifiques ont identifié des milliers de variations du génome qui existent ...

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genome variation in cnvs and snps

Genome variation in CNVs and SNPs shows how DNA can differ across people in a population. These differences may involve a single nucleotide, which is one DNA base, or a larger chromosomal change. Scientists study them to understand inherited variation in the human genome.

Copy number variations, or CNVs, are structural changes that cover more than 1 kb of DNA sequence. A CNV can change the number of copies of a gene or a group of genes. The main forms are deletion, tandem duplication, noncontiguous duplication, multiallelic CNV, and complex rearrangement.

A deletion removes a DNA segment and can lower gene copy number. In tandem duplication, a copied chromosomal segment is inserted next to the original region. In noncontiguous duplication, the copied segment moves to a distant chromosomal region or even a different chromosome. Multiallelic CNV creates several copies and can produce multiple alleles of a gene. In complex rearrangement, a segment duplicates and inverts before it is inserted back into the same or a different chromosome.

Single nucleotide polymorphism, or SNP, is another genomic variation that changes one nucleotide base. A SNP is a point mutation found in more than 1% of the population. Scientists have identified thousands of SNPs across the human genome, and they are widely used as genetic markers in studies of inherited disease and forensic analysis.

SNPs are grouped by use into four types. Identity-testing SNPs help distinguish people and exclude familial connections. Lineage informative SNPs are tightly linked SNPs that help identify missing individuals in family analysis. Ancestry informative SNPs help connect a person's ancestry with related phenotypic traits. Phenotype informative SNPs help estimate the chance of traits such as skin color or eye color.

Genome Variation in CNVs and SNPs

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comparing copy number variations and snps

Genome variation in CNVs and SNPs shows how DNA can differ across people in a population. These differences may involve a single nucleotide, which is one DNA base, or a larger chromosomal change. Scientists study them to understand inherited variation in the human genome. Copy number variations, or CNVs, are structural changes that cover more than 1 kb of DNA sequence. A CNV can change the number of copies of a gene or a group of genes. The main forms are deletion, tandem duplication,...

key terms and concepts

Explore how copy number variations and SNPs change the human genome, from deletions and duplications to ancestry, identity, and phenotype markers.

Genome Variation in CNVs and SNPs | JoVE K12

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Genome Variation in CNVs and SNPs

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