Name: how exons mix to form new genes
Uploaded: 2021-04-07T12:11:59.000Z
Duration: 2 min 32 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-1

Exon Recombination

تتكون الجينات حقيقية النواة من كتل متناوبة من تسلسلات ترميز البروتين تسمى exons والتسلسلات غير المشفرة تسمى الإنترونات.
إعادة تركيب الإكسون هي عملية يتم فيها تجميع الإكسونات من نفس الجينات أو جينات مختلفة لإنتاج مجموعات جديدة من تسلسل exon-intron ، والتي قد تتطور إلى جينات جديدة.
يمكن التوسط في إعادة تركيب exon عن طريق إعادة التركيب غير المتماثل أو التبديل الرجعي.
أثناء إعادة التركيب غير المتماثل أو غير الشرعي ، يمكن لخيوط الحمض النووي التي لا يوجد تشابه في التسلسل إعادة التجميع وإنتاج بنية جينية جديدة.
مرض الورم الحبيبي المزمن - اضطراب وراثي في الجهاز المناعي هو مثال جيد. يعاني العديد من المرضى الذين يعانون من هذا المرض من طفرة نادرة في ترميز جين phox لإنزيم NADPH oxidase.
ينتج النوع البري NADPH oxidase أنواعا من الأكسجين التفاعلي مثل الأكسيد الفائق عند الإصابة ويساعد في قتل العوامل المعدية بوساطة الخلايا البلعمة.
في حالات نادرة ، تتحد التسلسلات غير المتجانسة بين exons 8 و 11 من جين phox ، مما يتسبب في ازدواجية exons 9 و 10. هذا يؤدي إلى انخفاض نشاط إنزيم NADPH oxidase. يفشل الإنزيم الضعيف في توليد أنواع الأكسجين التفاعلية الكافية لإزالة العدوى البكتيرية مما يؤدي إلى الورم الحبيبي أو تراكم الضامة والخلايا المناعية المرتبطة بها. 
يمكن أن تفسر إعادة تركيب Exon بسبب التبديل الرجعي تطور جين Jingwei في ذبابة الفاكهة الأفريقية.
منذ حوالي 2.5 مليون سنة ، تم نسخ جزء من Adh mRNA بشكل عكسي إلى الحمض النووي وأعيد دمجها مع exons من جين Ynd لإنتاج جين جديد يسمى Jingwei.
جين Ynd مسؤول عن تطوير الخصيتين في ذبابة الفاكهة ويقوم جين Adh بتشفير نازعة هيدروجين الكحول. يقوم الجين الجديد Jingwei بتشفير بروتين بمجالين - أحدهما مشتق من Ynd والآخر من Adh.
ومن ثم ، يتم التعبير عن بروتين Jingwei في ذبابة الفاكهة الخصية وهو مسؤول عن التخليق الحيوي للهرمون والفرمون.

<ol>
	<li>لونغ ، مانيوان ، إستر بيتران ، كيفن ثورنتون ، وون وانغ. "أصل الجينات الجديدة: لمحات من الصغار والكبار". مراجعات الطبيعة علم الوراثة 4 ، العدد 11 (2003): 865-875.</li>
	<li>فان ريك وأنكي وهانز بلوميندال. "الآليات الجزيئية لخلط الإكسون: إعادة التركيب غير الشرعي". في أصل وتطور وظائف الجينات الجديدة ، ص 245-249. سبرينغر ، دوردريخت ، 2003.</li>
	<li>كولكمان ، جوست أ. ، وويليم بي سي ستيمر. "التطور الموجه للبروتينات عن طريق خلط exon". Nature Biotechnology 19 ، رقم 5 (2001): 423-428.</li>
	<li>لونج ، مانيوان. "تطور الجينات الجديدة". الرأي الحالي في علم الوراثة والتنمية 11 ، العدد 6 (2001): 673-680.</li>
</ol>

إعادة التركيب الإكسون

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إن تطور جينات جديدة أمر بالغ الأهمية لحدوث الانتواع. تعد إعادة تركيب الإكسون، والمعروفة أيضًا باسم خلط الإكسون أو خلط المجال، وسيلة مهمة لتكوين الجينات الجديدة. ويلاحظ في الفقاريات واللافقاريات وفي بعض النباتات مثل البطاطس وعباد الشمس. أثناء إعادة تركيب الإكسون، تتحد الإكسونات من نفس الجينات أو جينات مختلفة وتنتج مجموعات جديدة من إكسون-إنترون، والتي قد تتطور إلى جينات جديدة.

يتبع خلط الإكسون "قواعد إطار الوصلة". يحتوي كل إكسون على ثلاثة إطارات قراءة. يمكن للإكسونات الواردة إعادة توحيدها والانضمام إليها في أي واحد من إطارات القراءة الثلاثة وتسبب طفرات في تغيير الإطارات. لذلك، ليست كل أحداث إعادة التركيب مفيدة؛ يمكن أن يؤدي بعضها إلى كودون توقف سابق لأوانه وبروتين غير ناضج.

خلط الإكسونات في الجينوم البشري

-جنبا إلى جنب- مع ازدواجية الجينات وتباعدها، يُعزى خلط الإكسونات إلى تطور العديد من الجينات الخاصة بالإنسان. على سبيل المثال، منذ حوالي 25 مليون سنة، خضع جين يسمى MCH (هرمون تركيز الميلانين) لإعادة تركيب إكسون عن طريق إعادة النقل في الرئيسيات المبكرة. لقد خلقت حدودًا جديدة للإنترون-إكسون، والتي تطورت لاحقًا إلى الجين المحفوظ الخاص بأسلاف الإنسان PMCHL1 - على الرغم من أن هذا جين زائف، إلا أن الحمض النووي الريبي المضاد للاتجاه يتم التعبير عنه في الدماغ البشري. نظرًا لأن جين MCH الأصلي قام بتشفير الببتيد العصبي المشارك في موازنة متطلبات الطاقة ووزن الجسم في القوارض، فمن المتوقع أن يكون لـ PMCHL-1 وظائف مماثلة.

تعد إعادة التركيب غير المشروعة (IR) إحدى الآليات الأكثر شيوعًا لإعادة التركيب إكسون أو خلط إكسون. الأشعة تحت الحمراء يؤدي إلى ازدواجية الإكسونات؛ وقد لوحظ هذا في العديد من الأمراض التي تصيب الإنسان مثل الحثل العضلي دوشين وبيكر، وفرط كوليستيرول الدم العائلي، ومتلازمة ليش نيهان، والهيموفيليا، ونقص الليباز البروتيني الدهني.
</div>

يعد تطور الجينات الجديدة أمرا بالغ الأهمية للانتواع. إعادة تركيب Exon ، المعروف أيضا باسم خلط exon أو خلط المجال ، هو وسيلة مهمة ل ...

Education

JoVE Core

Molecular Biology

البيولوجيا الجزيئية

Unit 2

الوحدة الثانية

Genomes and Evolution

الجينومات والتطور

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 exon has three reading frames. Incoming exons can join in any one of the three frames, and that can cause a frameshift mutation. Because of this, not every recombination event is helpful. Some events can create a premature stop codon and a protein that is not fully made.

In human evolution, exon shuffling has helped shape several human-specific genes. It worked alongside gene duplication and divergence. One example is the MCH gene, which underwent exon recombination by retrotransposition about 25 million years ago in early primates.

That event created new intron-exon boundaries, which later evolved into the Hominidae-specific conserved gene PMCHL1. PMCHL1 is a pseudogene, but its antisense RNA is expressed in the human brain. Because the original MCH gene encoded a neuropeptide involved in energy balance and body weight in rodents, PMCHL-1 is expected to have similar functions.

Illegitimate recombination is one of the most common ways exon recombination happens. It can duplicate exons and has been seen in several human diseases, including Duchenne and Becker muscular dystrophy, familial hypercholesterolemia, Lesch-Nyhan syndrome, hemophilia, and lipoprotein lipase deficiency.

How Exons Mix to Form New Genes

evolutionary relationships through genome comparisons

evolutionary-relationships-through-genome-comparisons

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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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synteny and evolution

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multi-species conserved sequences

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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

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

comparing-copy-number-variations-and-snps

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,...

key terms and concepts

Exon recombination, or exon shuffling, can create new gene combinations. Learn how reading frames, frameshifts, and human gene examples fit this process.

How Exons Mix to Form New Genes | JoVE K12

molecular biology

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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Ohio’s Learning Standards and Model Curriculum

9-12

Biology

Evolution

Speciation

Tennessee Academic Standards

Heredity

BIO1.LS3.2

Virginia  Standards of Learning

HIgh School

BIO.5

BIO.5.d

Minnesota Academic Standards in Science

Life Science

3.2.1 9L.3.2.1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Biological Evolution: Unity and Diversity

Arizona Science Standards

HS+B.L3

HS+B.L3U1.12

HS+B.L4

HS+B.L4U1.13

Alabama Course of Study Science

Unity and Diversity

9-12.B.4.13

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HS-LS4-5

How Exons Mix to Form New Genes

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