Name: how genome size shapes new genes
Uploaded: 2020-11-23T11:47:33.000Z
Duration: 3 min 21 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Biology

Biological Evolution- Unity and Diversity

LS.Bio.9.2

genome-size-and-the-evolution-of-new-genes

Genome Size and the Evolution of New Genes

رغم بساطة طبيعة الشفرة الجينية هناك اختلاف كبير من حيث حجم الجينوم من الأصغر و المعروف بالجينوسوم التى تتضمن البروتيوباكتيريا كانديداتوس كارسونيلا التى أنصاف اقطارها أقل من 160.000 زوج من القواعد إلى اكبرها, مثل النبات المزهر اليابانى باريس جابونيكا يبلغ حوالي 150 مليار. على الرغم من هذا الاختلاف الشديد البكتيريا والعتائق عندها حوالي 3000 جين داخل جينوماتهم لأن بدائيات النوى تقريبا لا توجد لديها تسلسلات غير مشفرة هذا يعني ان الجينومات الخاصة بهم تكون صغيرة نسبيًا مقارنة بأولئك من حقيقيات النوى. الجينوم الاصفر أيضا يعني الاقل فى الاستنساخ في كل دورة من دورات انقسام الخلايا والذى له معنى لوجستي للتكاثر السريع حقيقيات النوى إجمالا بها تقريبا 20000جين ولكن جينوماتها تتخللها امتدادات طويلة التسلسل غير مشفرة مما يعني ان حجم الجينوم الخاص بهم ليس بالضرورة أن يترجم الى شىء معقد جينوم باريس جابونيكا قد يكون أكبر 50 مرة من حجم جينوم الإنسان, لكن هذا يرجع على الأقل جزئيًا إلى كميات كبيرة من التسلسل غير المشفر وربما مستويات عالية من التكرار ليس بالضرورة المزيد من الجينات الجديدة.

فكيف إذن تُطور الكائنات الحية جينات جديدة؟الجواب عادة بواسطة تعديل التسلسل الذى هو موجود أصلا. أحد الموارد الأساسية لتطور جينات جديدة هو من خلال التكرار الجينيى تخيل قسم من الحمض النووي يحتوى على جين تكرر بطريق الخطأ. الآن الكائن الحي لديه نسخة ثانية من الجين الموجود.

هذه النسخ الجينية الجديدة حرة من القيود الموضوعة على الأصل للحفاظ على الوظيفة وهكذا يستطيعون ان يتنوعوا, ومن المحتمل يحدث تطوير دور جديد أو تعديل لوظيفة أصلية طريقة أخرى لخلق جينات جديدة هي خلط دى إن أيه حيث أجزاء من جين موجود او من نسخة جين يتم فصلها والانتقال للانضمام لأجزاء من جين مختلف صانعا بذلك جين هجين يمكن أن يقوم بوظيفة جديدة الطفرة داخل الجين هى التغييرات في تسلسل الجينات المدمجة عن طريق الطفرات بمرور الوقت وهذه تفسر العديد من الجينات الجديدة هذا التنوع هو الأكثر وضوحا عند مقارنة الأنواع أو الأنساب التي تتنوع بشكل مستقل. بمجرد أن يكون هذا التنوع وراء نقطة معينة أو جين واحد يقوم بوظيفة جديدة يمكن تصنيفها على أنها جينات مختلفة تمامًا. أخيرًا النقل الافقى للجينات يجلب جينات وتسلسلات جديدة إلى الجينوم من مصادر خارجية مثل الأفراد الآخرين وحتى الأنواع الأخرى.

هذا النوع من الجينات الجديدة المكتسبة هو الأكثر شيوعًا في بدائيات النوى والعتائق مع النقل للجينات مقاومة المضادات الحيوية كونه مثالًا معروفًا. بينما نادر في حقيقيات النوى انها لا تزال تُعتبر مصدر أساسي للجينات الجديدة والمواد الجينية يمكن أن تأتي من انواع بعيدة الصلة مثل البكتيريا والفطريات في هذا المثال.

حجم الجينوم وتطور الجينات الجديدة

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في حين أن كل كائن حي لديه جينوم من نوع ما (سواء كان RNA أو DNA)، إلا أن هناك تباينًا كبيرًا في أحجام هذه المخططات. أحد العوامل الرئيسية التي تؤثر على حجم الجينوم هو ما إذا كان الكائن الحي بدائي النواة أو حقيقي النواة. في بدائيات النوى، يحتوي الجينوم على القليل من التسلسل غير المشفر أو لا يحتوي على أي تسلسل، بحيث تتجمع الجينات بإحكام في مجموعات أو مشغلات بشكل تسلسلي على طول الكروموسوم. وعلى العكس من ذلك، فإن الجينات الموجودة في حقيقيات النوى تتخللها فترات طويلة من التسلسل غير المشفر. بشكل عام، يساهم هذا في ظاهرة أن جينومات بدائيات النوى تميل إلى أن تكون أصغر (أي تحتوي على عدد أقل من القواعد) في المتوسط من جينومات حقيقيات النوى.

ومن غير المستغرب، في ضوء هذه الملاحظة، أن أصغر الجينومات المعروفة هي في الغالب بدائيات النوى. على سبيل المثال، تعد كانديداتوس كارسونيلا رودي (Candidatus Carsonella rudii) من البكتيريا البروتينية المبسطة للغاية والتي يبلغ حجم جينومها 160 ألف زوج قاعدي فقط. بعد أن فقدت العديد من الجينات التي كانت بحاجة إليها لتصنيع البروتينات الأساسية للحياة، تطورت لتصبح متكافلة إلزامية داخل الخلايا. وفي الطرف المقابل من الطيف، يعد النبات الزهري الياباني حقيقي النواة باريس جابونيكا واحدًا من أكبر الجينومات المعروفة، حيث يضم حوالي 150 مليار زوج قاعدي. على الرغم من أن عدد الجينات التي يشفرها هذا غير معروف، إلا أن الجينوم يُظهر كميات هائلة من التكرار والتسلسل غير المشفر.

يوجد داخل جينوم بدائيات النوى المتوسطة ما يقرب من 3000 جين. يبلغ متوسط عدد حقيقيات النوى في مكان ما حوالي 20000. لكن حجم الجينوم، وخاصة في حقيقيات النوى، متغير بشكل كبير - ويرجع ذلك إلى حد كبير إلى كمية التسلسل غير المشفر.

خلق جينات جديدة

من أجل تطوير جينات جديدة، لدى الكائنات الحية عدد قليل من الخيارات الرئيسية. الشيء الوحيد المشترك بين معظم هذه العناصر هو أنها تقوم بتعديل التسلسلات الموجودة بالفعل.

يلعب التضاعف دورًا مهمًا في تكوين جينات جديدة، وهناك أنواع قليلة من التضاعف التي يمكن أن تؤدي إلى هذه التسلسلات الجديدة. في ازدواج الجينات، يتم تكرار جزء من الحمض النووي الذي يحتوي على الجين. هذه النسخة الثانية لا تواجه ضغط الاختيار الذي يقيد الأولى، وبالتالي يمكن أن تتباعد. وبمرور الوقت، يمكن أن يؤدي هذا إلى تطور جينات جديدة لها أدوار جديدة.

هناك نوع آخر من التضاعف - خلط الحمض النووي - يمكن أن يؤدي إلى تكرار جزء فقط من الجين وانضمامه إلى جين آخر. وهذا يمكن أن يؤدي إلى خلق جينات جديدة، مع منتجات جديدة.

في بعض الأحيان تتطور الجينات الجديدة ببساطة من الطفرات المتراكمة مع مرور الوقت. يُعرف هذا بالطفرة داخل الجينات، ويكون أكثر وضوحًا عند المقارنة بين الأنواع أو المجموعات المتباينة.

وأخيرا، من الممكن أيضا الحصول على جينات جديدة من مصادر خارجية، في عملية تعرف باسم نقل الجينات الأفقي. وهذا يعني أنه يمكن دمج المادة الوراثية من أفراد آخرين، وأحيانًا من نفس النوع، ولكن من المحتمل أيضًا أن تكون من نوع آخر تمامًا. وهذا مصدر متكرر للجينات الجديدة في بدائيات النوى والعتائق. وهو أقل شيوعًا في حقيقيات النوى، ولكن ثبت حدوثه، ويمكن لحقيقيات النوى حتى التقاط المعلومات الوراثية من مصادر بعيدة مثل البكتيريا أو الفطريات.
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في حين أن كل كائن حي لديه جينوم من نوع ما (سواء كان الحمض النووي الريبي أو الحمض النووي) ، إلا أن هناك تباينا كبيرا في أحجام هذه المخططات. تخصص واحد ...

Education

JoVE Core

Molecular Biology

البيولوجيا الجزيئية

Unit 1

الوحدة الأولى

DNA, Cells, and Evolution

الحمض النووي، والخلايا، والتطور

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

how genome size shapes new genes

Genome size can vary widely, and it also helps show how new genes form. Every living organism has a genome, whether it uses RNA or DNA. Yet the size of that genome can be very different from one organism to another.

One major difference is whether the organism is prokaryotic or eukaryotic. Prokaryotic genomes usually have little to no non-coding sequence, which means genes are packed closely together in operons along the chromosome. Eukaryotic genomes contain long stretches of non-coding DNA between genes. This helps explain why prokaryotic genomes are often smaller than eukaryotic genomes.

The smallest known genomes are mostly prokaryotic. One example is Candidatus Carsonella rudii, a highly simplified proteobacterium with a genome of only 160 thousand base-pairs. It has lost many genes needed to make life-essential proteins, so it now lives as an obligate intracellular symbiont. On the other end of the range, the Japanese flowering plant Paris japonica has one of the largest known genomes, at about 150 billion base-pairs. Its genome contains extensive duplication and non-coding sequence, and the number of genes it encodes is not known.

Gene counts also differ between these groups. An average prokaryote has roughly 3,000 genes. An average eukaryote has around 20,000 genes. Even so, genome size in eukaryotes can vary a great deal because of how much non-coding DNA they contain.

New genes usually arise by changing sequences that already exist. Gene duplication copies a DNA segment that contains a gene. The extra copy is not under the same selection pressure as the original, so it can change over time and take on a new role. DNA shuffling can duplicate only part of a gene and join it to another gene, which can create a new gene product.

New genes can also appear through intragenic mutation, which means mutations build up within a gene over time. This is often seen when comparing different species or populations that have diverged. Another source is horizontal gene transfer, where genetic material comes from another individual or even another species. This is a common way for prokaryotes and archaea to gain novel genes, although it can also happen in eukaryotes, including gene transfers from bacteria or fungi.

How Genome Size Shapes New Genes

the dna helix

DNA Structure and Base Pairing

DNA has a helical structure that helps store genetic information. The double helix is the shape formed by two strands that twist around each other. This structure is a key feature of DNA in cells. The two strands are held together by base pairing. Bases on one strand match with bases on the other strand in a regular way. This pairing helps keep the DNA molecule stable and organized. The helix shape also helps explain how DNA fits into chromosomes and carries instructions for living things. By...

the central dogma

DNA to Protein: Central Dogma Steps

The central dogma explains how genetic information moves from DNA to RNA to protein. This flow is a key idea in molecular biology. It helps show how cells use genes to make the molecules that carry out work. DNA stores the instructions for making proteins. During transcription, a gene in DNA is copied into RNA. The RNA then carries that message to the next stage. In translation, the RNA message is used to build a protein. Proteins do much of the cell’s work, so this process connects genes to...

prokaryotic cells

Inside Prokaryotic Cell Structure

Prokaryotic cells have a simple internal structure compared with many other cells. They are usually divided into two groups: bacteria and archaea. These cells have no nucleus, so their DNA is not enclosed in a membrane-bound compartment. Instead, the genetic material is found in the nucleoid, a region where the DNA is located in the cell. Some prokaryotic cells also contain plasmids, which are small extra DNA molecules. A capsule may surround the cell and provide an additional outer layer. <br...

eukaryotic compartmentalization

Cell Compartments in Eukaryotes

Eukaryotic cells use compartments to organize many different jobs inside one cell. These compartments help separate processes so they can happen in the right place. The compartment called the cytosol is the fluid part of the cell. It surrounds the other internal structures and helps support many cell processes. Inside the cell, membrane-bound organelles create distinct microenvironments. A microenvironment is a small internal space with conditions that fit a specific task. This separation...

the tree of life - bacteria, archaea, eukaryotes

the-tree-of-life-bacteria-archaea-eukaryotes

How Life Is Classified Into Three Domains

The tree of life shows how organisms are related through evolution. Its root represents the common ancestor of all life on Earth. From that point, branches spread out like a tree. The tips of the branches represent living, or extant, species. Species that no longer exist, called extinct species, appear closer to the center of the tree. Today, these organisms are grouped into three domains: bacteria, archaea, and eukaryotes. Scientists still debate these divisions, so the tree of life keeps...

mutations

How Mutations Change DNA

Mutations are changes in DNA. They can alter the genetic code and affect how genes work. In high school biology, students often study mutations to understand how DNA changes can influence traits. The transcript focuses on two common mutation types: point mutations and frameshift mutations. A point mutation changes one nucleotide, which is one DNA building block. A frameshift mutation happens when nucleotides are added or removed and the reading frame shifts. These changes matter because they...

gene evolution - fast or slow?

Why Some Gene Regions Evolve Faster

Gene regions do not all change at the same rate. In eukaryotes, long stretches of DNA do not code for proteins or RNAs. Some of these non-coding regions include important regulatory sequences, but most have no known function. Because little or no selection pressure acts on them, they often change the fastest over evolutionary time. Protein-coding regions usually evolve more slowly. A change in a coding sequence can alter a protein and make it less effective at doing its job. That creates...

genome size and the evolution of new genes

Genome size can vary widely, and it also helps show how new genes form. Every living organism has a genome, whether it uses RNA or DNA. Yet the size of that genome can be very different from one organism to another. One major difference is whether the organism is prokaryotic or eukaryotic. Prokaryotic genomes usually have little to no non-coding sequence, which means genes are packed closely together in operons along the chromosome. Eukaryotic genomes contain long stretches of non-coding DNA...

gene families

How Gene Families Evolve and Diversify

Gene families are groups of genes that are thought to come from a shared ancestor. They usually form when a gene is copied by mistake during cell division. The original gene stays under selection pressure to keep its job, while the extra copy can change more quickly over time. Some copied genes gain a new role in the organism. When that happens, they are called paralogs, which are two genes in the same species that evolved from one common ancestral gene. Gene families also include orthologs,...

types of genetic transfer between organisms

types-of-genetic-transfer-between-organisms

How Genes Move Within and Across Generations

Genetic transfer is the movement of genetic information from one organism to another. It happens in two main ways: vertical gene transfer and horizontal gene transfer. Vertical gene transfer moves genes from one generation to the next. It is much more common than horizontal gene transfer. Vertical gene transfer happens during both sexual reproduction and asexual reproduction. In both cases, one or more organisms pass some or all of their genome to their offspring. This kind of transfer occurs...

key terms and concepts

Compare prokaryotic and eukaryotic genome sizes, then see how gene duplication, DNA shuffling, mutation, and horizontal gene transfer create new genes.

How Genome Size Shapes 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.

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

New Jersey Student Learning Standards for Science

High School

Life Science

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-1

Florida Department of Education

SC.912.L.15

SC.912.L.15.2

Development of Antibiotic Resistance

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Understanding Species and Reproductive Barriers

A species is a group of organisms that interbreed and produce fertile offspring. Typically, individuals of the same species appear similar and share ...

Formation of Species

Speciation describes the formation of one or more new species from one or sometimes multiple original species. The resulting species are discrete from the ...

Speciation Rates

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Genetics of Speciation

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Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may ...

What is Natural Selection?

Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become ...

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural ...

Frequency-dependent Selection

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 ...

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly ...

Natural Selection

Fitness
Widespread variation of phenotypes in natural populations provides the raw material for evolution, which is the change in the inherited traits of ...

Simulating Natural Selection
ExpandTo prepare for the lab, set out workstations for each student pair containing 6 white, 6 black, and 13 gray 12 inch ...

Simulating Natural Selection
ExpandTo begin, cut the white, black, and gray pipe cleaners into quarters, which should produce a total of 100 pieces that ...

Artificial Selection

Natural Selection and Adaptive Evolution
In natural settings, adaptive evolution takes place by natural selection, a process in which differences in ...

Observing Artificial Selection in Plants
ExpandTwo weeks before beginning the pollination experiments, collect a sufficient amount of small pots with a ...

Observing Artificial Selection in Plants 
ExpandTo begin the experiment, collect five two-week old grown plants from the generation one population that ...

Analyze and interpret data to summarize how various factors such as geographic isolation, pesticide resistance, antibiotic resistance can influence natural selection.

LS.Bio.9.1

Phylogenetic Trees

Phylogenetic trees come in many forms. It matters in which sequence the organisms are arranged from the bottom to the top of the tree, but the branches ...

Conditions on Early Earth

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen ...

The Colonization of Land

Changes in the environment of the early Earth drove the evolution of organisms. As prokaryotic organisms in the oceans began to photosynthesize, they ...

What is Evolutionary History?

Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and ...

The Evidence for Evolution

Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of ...

The Fossil Record

The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms ...

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure ...

Gene Evolution - Fast or Slow?

The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain ...

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major ...

Gene Families

Gene families consist of groups of genes proposed to have originated from a common ancestor. Typically these arise through events in which a gene or genes ...

Types of Genetic Transfer Between Organisms

Genetic transfer occurs when genetic information is passed from one organism to another. It occurs via two mechanisms: vertical gene transfer and ...

Ribozymes

The term ribozyme is used for RNA that can act as an enzyme. Ribozymes are mainly found in selected viruses, bacteria, plant organelles, and lower ...

Construct an explanation to illustrate how common ancestry and biological evolution are supported by multiple lines of empirical evidence.

Use models to illustrate the conditions required for natural selection, including the overproduction of offspring, inherited variation, and the struggle to survive.

LS.Bio.9.3

Construct an explanation to explain how natural selection leads to adaptations within populations.

LS.Bio.9.4

Extinction

The History of Life on Earth
Fossils of organisms that were different from anything alive today had been documented as early as the 17th century, but it ...

Diversity and Extinction during the Paleogene Epoch
ExpandFirst, familiarize yourself with the extinction reading supplement for the background on what ...

Diversity and Extinction during the Paleogene Epoch
ExpandBegin this procedure by reading the extinction reading supplement that has been printed out for ...

Construct explanations to illustrate how varying environmental conditions may result in: changes in the number of individuals of a species, the emergence of new species over time, or the extinction of other species.

LS.Bio.10.1

Synteny and Evolution

John H. Renwick first coined the term &#8220;synteny&#8221; in 1971, which refers to the genes present on the same chromosomes, even if they are not ...

Multi-species Conserved Sequences

Next-generation sequencing technologies have created large genomic databases of a variety of animals and plants. Ever since the human genome project was ...

Taxonomy

Taxonomy is the science of defining and naming groups of biological organisms based on shared characteristics. It uses a hierarchy of increasingly ...

Phylogeny

Phylogeny is concerned with the evolutionary diversification of organisms or groups of organisms. A group of organisms with a name is called a taxon ...

Use models (including dichotomous keys, scientific nomenclature, cladograms, phylogenetic trees) to identify organisms and exemplify relationships.

LS.Bio.10.2

Understand natural selection as a mechanism for biological evolution.

How Genome Size Shapes New Genes

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