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

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-1

comparing-copy-number-variations-and-snps

Comparing Copy Number Variations and SNPs

שינויים גנומיים כגון הוספה או מחיקה של מקטעי DNA נצפים בדרך כלל באוכלוסייה. שינויים גנומיים באוכלוסייה יכולים להיווצר עקב שינויים בנוקלאוטידים בודדים בדנ"א או שינויים מבניים בכרומוזומים.
וריאציה של מספר העתק או CNV הוא מונח גג המגדיר את השינויים המבניים הכוללים מקטעי DNA של יותר מזוג בסיסים של קילו אחד.
אם המקטע הכרומוזומלי המעורב מכיל גן, CNV יכול להגדיל את מספר העותקים של הגן על ידי שכפול והחדרה או להקטין אותו על ידי מחיקה שתוצאתה גנוטיפ ריק.
לכן, לאנשים מסוימים עשויים להיות שני עותקים או אפילו יותר של גן, או ללא עותקים כלל. לדוגמה, אנשים מסוימים ממוצא גנטי אירופי עשויים לשאת שני עותקים של הגן קבוצת הדם רזוס, RHD, בעוד שלחלקם יש רק אחד ולאחרים אין כלל.  
CNV יכול להשפיע על הפנוטיפים התלויים במספר עותקי הגנים הפונקציונליים. באזורים אירופיים-אמריקאים ואסיאתיים שבהם תזונה מבוססת עמילן נפוצה, האוכלוסייה מראה מספר העתקים גבוה יותר של הגן AMY1, גן המעורב במטבוליזם של עמילן.
CNV קשורים גם למספר מחלות כגון פסוריאזיס, פרקינסון והפרעות התנהגותיות כמו אוטיזם וסכיזופרניה.
בעוד CNV בדרך כלל מכסים וריאציות גדולות של רצפי DNA, פולימורפיזמים של נוקלאוטידים בודדים או SNPs הם תחליפי בסיס יחיד אקראיים הנמצאים ברחבי הגנום.
החלפות בסיס כאלה מתרחשות אחת ל-1000 נוקלאוטידים; עם זאת, לא כולם מתאימים ל-SNPs. בדרך כלל, רק וריאציה נוקלאוטידים שנמצאת ביותר מ -1% מהאוכלוסייה מכונה SNP.
SNPs יכולים להעניק מחלות שונות כגון סוכרת או סרטן. לדוגמה, בחולים עם אנמיה חרמשית, החלפת בסיס יחיד מאדנין לתימין במיקום ספציפי של הגן בטא-גלובין גורמת לתאי דם אדומים בצורת מגל.

<ol>
	<li>לי, צ'ארלס וסטיבן שרר. "ההקשר הקליני של וריאציה של מספר עותקים בגנום האנושי." חוות דעת מומחה ברפואה מולקולרית 12 (2010).</li>
	<li>בודול, ברוס ואנג'לה ואן דאל. "שיעורי SNP רלוונטיים מבחינה משפטית". ביוטכניקה 44, מס '5 (2008): 603-610.</li>
</ol>

השוואת וריאציות מספר העתקות ו-snps

<div style="direction: rtl;">
ריצוף של הגנום האנושי פתח כמה סודות השמורים ביותר של הגנום. מדענים זיהו אלפי וריאציות גנום הקיימות בתוך אוכלוסייה. וריאציות אלו יכולות להיות נוקלאוטיד בודד או וריאציה כרומוזומלית גדולה יותר.

וריאציות של מספר העתקות או CNVs הן הווריאציות המבניות המכסות יותר מ-1kb של רצף DNA. לעומת זאת, פולימורפיזם נוקלאוטיד בודד (SNP) הוא שינוי נוקלאוטיד בודד או מוטציה נקודתית שנמצאת ביותר מ-1% מהאוכלוסייה. גם CNV וגם SNPs הם בעלי ערך רב במחקרי סקר גנטיים וניתוח קרבה.

צורות של CNVs.

ישנן חמש צורות של CNVs. הראשון נקרא מחיקה. אובדן של קטע דנ"א יכול להפחית את מספר ההעתקים של גן או קבוצת גנים. השני נקרא שכפול טנדם. כאן, עותק של מקטע כרומוזומלי מוכנס לאזור סמוך. השלישי נקרא שכפול לא רציף. כאן, מקטע כרומוזומלי משתכפל וחודר לאזור כרומוזומלי מרוחק או כרומוזום אחר. הצורה הרביעית נקראת Multiallelic CNV. קטע של דנ"א משתכפל מספר פעמים ומביא ליצירת אללים מרובים של גן. הצורה החמישית נקראת סידור מחדש מורכב. כאן קטע של דנ"א משתכפל ומתהפך לפני שהוא מוחדר בחזרה לאותו כרומוזום או אחר.

פולימורפיזם נוקלאוטיד בודד

פולימורפיזם נוקלאוטיד בודד או SNP הוא סוג נוסף של וריאציה גנומית הכוללת שינויים בבסיס נוקלאוטיד בודד. מדענים זיהו אלפי SNPs ברחבי הגנום האנושי, והם משמשים באופן שגרתי כסמנים גנטיים למחלות תורשתיות ולניתוח משפטי.

בהתבסס על היישום שלהם, SNPs מחולקים לארבעה סוגים. SNPs לבדיקת זהות משמשים כדי להבדיל בין אנשים ולחסל אנשים מקשרים משפחתיים. SNPs אינפורמטיבי של שושלת הם SNPs מקושרים הדוקים המסייעים לזהות פרטים נעדרים בניתוח משפחתי. SNPs אינפורמטיביים של מוצא עוזרים לבסס את מוצאו של אדם ולחבר אותו עם המאפיינים הפנוטיפיים שלו. SNPs אינפורמטיביים לפנוטיפ קובעים את ההסתברות לרשת פנוטיפ מסוים, כגון צבע עור, צבע עיניים וכו'.
</div>

השוואת וריאציות מספר העתקות ו-SNPs

ריצוף הגנום האנושי חשף כמה סודות שמורים ביותר של הגנום. מדענים זיהו אלפי וריאציות גנום הקיימות ...

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Molecular Biology

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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

evolutionary relationships through genome comparisons

evolutionary-relationships-through-genome-comparisons

Tracing Evolution with Genome Data

Genome data helps scientists trace how organisms are related over time. When two species share a common feature, it is often encoded by DNA sequences that have stayed conserved in both species. As genome sequencing improved in the late 20th century, researchers gained a better way to compare conserved domains across species and use that evidence to infer evolutionary relationships. Genome comparison can show evolutionary relationships at three levels. At the broadest level, it highlights...

genome copying errors

DNA Replication Error Checks

DNA replication includes built-in error checks that protect the genome during cell division. Even though this process copies millions of base pairs with high fidelity, a wrong base or a longer stretch of wrong bases can still be added to the daughter strands. If these mistakes are not corrected, cells may build up mutations that can threaten survival. One level of repair is proofreading. DNA polymerase enzymes, which build the new DNA strand, can make about 1 incorrect nucleotide per 100,000...

phylogenetic trees

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Phylogenetic trees show how organisms are related through evolution. They map branching patterns that trace common ancestry and help scientists compare species over time. A phylogenetic tree can be read like a family tree for life. Each branch point marks a split from a shared ancestor, and the pattern of branches shows how closely related different organisms are. These trees are used to organize biological information and to study evolutionary change. They can also help scientists understand...

synteny and evolution

Chromosome Rearrangements and Synteny

Chromosome rearrangements and synteny show how shared gene order can reveal evolutionary history. Synteny means genes are found on the same chromosome, even if they are not genetically linked. John H. Renwick coined the term in 1971. Species with common ancestry often keep conserved syntenic regions. Scientists use synteny to compare the evolutionary relationship between species. Human and mouse lineages split from a common ancestor about 80 million years ago. Since then, the ancestral...

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gene duplication and divergence

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Gene duplication helps drive evolution by creating extra copies of DNA that can change over time. The seminal work of Ohno in 1970 helped popularize this idea. DNA sequence comparisons show that many genes in bacteria, archaebacteria, and eukaryotes came from duplication and later divergence, which makes this process important in evolution. The duplicated copies of a gene are called paralogs. When paralogs have similar sequences and functions, they form a gene family. Many gene families have...

exon recombination

How Exons Mix to Form New Genes

Exon recombination helps new genes form by mixing exons from the same gene or from different genes. This process is also called exon shuffling or domain shuffling. It has been seen in vertebrates, invertebrates, and some plants, including potatoes and sunflowers. During exon recombination, exons join in new exon-intron combinations. These new combinations may later become new genes. Exon shuffling follows splice frame rules, which means the exons must fit the reading frame correctly. Each...

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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JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

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Biological Evolution: Unity and Diversity

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This ...

Construct an explanation based on evidence that biological diversity is influenced by (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs or proportional reasoning.

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Apply concepts of statistics and probability to support explanations that populations of organisms adapt when an advantageous heritable trait increases in proportion to organisms lacking this trait. Emphasis is on analyzing shifts in numerical distribution of traits and using these shifts as evidence to support explanations for adaptations. Explanations could include basic statistical or graphical analysis.

HS-LS4-3

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Evaluate evidence supporting claims that changes in environmental conditions can affect the distribution of traits in a population causing: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species. Emphasis is on determining cause and effect relationships for how changes to the environment such as deforestation, overfishing, application of fertilizers, drought, flood, and the rate of change of the environment affect distribution or disappearance of traits in species.

HS-LS4-5

Genome Variation in CNVs and SNPs

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