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

遺伝暗号の単純な性質にもかかわらず、ゲノムサイズの点では、16万塩基対未満のプロテオバクテリウムCandidatus Carsonella ruddiiを含む最小の既知のゲノムから、約1,500億の日本の顕花植物パリジャポニカのような最大のゲノムまで、かなりのバリエーションがあります 
 
これらの極端な違いにもかかわらず、細菌や古細菌は一般的にゲノム内に約3,000の遺伝子を持っています。原核生物はノンコーディング配列をほとんど持たないため、真核生物に比べてゲノムが比較的小さい可能性があります。また、ゲノムが小さいということは、細胞分裂の各ラウンドで複製する量が少なくなるということであり、これは迅速な複製のためにロジスティック的に理にかなっています。
真核生物は通常、20,000個の遺伝子を持っていますが、そのゲノムは長いノンコーディング配列によって中断されているため、ゲノムサイズが必ずしも複雑さにつながるわけではありません。 
パリス・ジャポニカのゲノムは、ヒトゲノムの50倍以上の大きさであるかもしれないが、これは少なくとも部分的には、膨大な量の非コード配列とおそらく高レベルの重複によるものであり、必ずしも新しい遺伝子が多いわけではない。
では、生物はどのようにして新しい遺伝子を進化させるのでしょうか?その答えは、通常、すでに存在するシーケンスを変更することです。
新しい遺伝子が進化するための主要なリソースの1つは、遺伝子の重複によるものです。遺伝子を含むDNAの一部が誤って複製されたと想像してみてください。これで、生物は既存の遺伝子の2番目のコピーを持っています。 
このような新しい遺伝子コピーは、機能を維持するためにオリジナルに課せられた制約から解放されるため、分岐することができ、新しい役割やオリジナルの変更された機能を進化させる可能性があります。 
新しい遺伝子を作成する別の方法は、DNAシャッフル(既存の遺伝子または遺伝子コピーのセグメントを分離して移動させ、別の遺伝子のセグメントを結合させる)であり、新しい機能を担うことができるハイブリッド遺伝子を作成します。
遺伝子内突然変異 - 突然変異によってもたらされる遺伝子配列の変化は、多くの「新しい」遺伝子の原因となります。この相違は、それ自体が独立して分岐している種や系統を比較するときに最も顕著です。この分岐が特定のポイントを超えると、または1つの遺伝子が新しい機能を持つようになると、それらはまったく異なる遺伝子として分類される可能性があります。
最後に、遺伝子の水平導入は、他の個体や他の種などの外部ソースからゲノムに新しい遺伝子と配列を取り込みます。このタイプの新規遺伝子獲得は、原核生物と古細菌で最も一般的であり、抗生物質耐性遺伝子の移植はよく知られた例です。 
真核生物では珍しいですが、それでも遺伝的新規性の不可欠な源であると考えられており、遺伝物質は、この例の細菌や真菌などの遠縁種からも得られる可能性があります。

ゲノムサイズと新しい遺伝子の進化

すべての生物は何らかのゲノム (RNA または DNA) を持っていますが、これらの設計図のサイズにはかなりのばらつきがあります。 ゲノムサイズに影響を与える主な要因の1つは、生物が原核生物であるか真核生物であるかです。 原核生物では、ゲノムには非コード配列がほとんどまたはまったく含まれず、そのため、遺伝子は染色体に沿って連続的にグループまたはオペロンとして緊密にクラスター化されています。 逆に、真核生物の遺伝子は、長い非コード配列によって中断されています。 全体として、これは、原核生物のゲノムが真核生物のゲノムよりも平均して小さい（つまり、含まれる塩基が少ない）傾向があるという現象に寄与しています。

この観察を考慮すると、当然のことながら、既知の最小のゲノムはほとんどが原核生物です。 たとえば、カルソネラ・ルディアイ (Candidatus Carsonella ruddii) は高度に単純化されたプロテオバクテリアで、ゲノムサイズはわずか 16 万塩基対です。 生命必須タンパク質の合成に必要な多くの遺伝子を失ったため、偏性細胞内共生生物へと進化した。 スペクトルの対極にある真核生物である日本の顕花植物パリジャポニカは、知られている中で最大のゲノムの1つであり、その数は約 1,500 億塩基対です。 これがコードする遺伝子の数は不明ですが、ゲノムには膨大な量の重複と非コード配列が示されています。

平均的な原核生物のゲノム内には、およそ 3,000 個の遺伝子があります。 平均的な真核生物には約 20,000 個の遺伝子が存在します。しかし、特に真核生物のゲノムサイズは、主に非コード配列の量によって大きく異なります。

新しい遺伝子の創造

新しい遺伝子を進化させるために、生物にはいくつかの主な選択肢があります。 これらのほとんどに共通することは、すでに存在するシーケンスを変更することです。

重複は新しい遺伝子の作成において重要な役割を果たしており、これらの新しい配列をもたらす可能性のある重複にはいくつかの種類があります。 遺伝子複製では、遺伝子を含む DNA の部分が複製されます。 この 2 番目のコピーは、最初のコピーを制約する選択圧力に直面しないため、分岐する可能性があります。やがて、これは新しい役割を持つ新しい遺伝子の進化につながる可能性があります。

別のタイプの複製である DNA シャッフリングでは、遺伝子の一部だけが複製され、別の遺伝子が結合する可能性があります。 これにより、新しい遺伝子が作成され、新しいタンパク質が生み出される可能性があります。

新しい遺伝子は、時間の経過とともに蓄積された突然変異から単純に進化する場合があります。 これは遺伝子内突然変異として知られており、種間または異なる集団間で比較する場合に最も顕著です。

最後に、水平遺伝子伝達として知られるプロセスで、外部ソースから新しい遺伝子を取得することも可能です。 これは、遺伝物質が他の個体、時には同じ種の個体から組み込まれる可能性があることを意味しますが、完全に別の種に由来する可能性もあります。 これは、原核生物や古細菌における新規遺伝子の頻繁な供給源です。 真核生物ではそれほど一般的ではありませんが、発生することが示されており、真核生物は細菌や真菌と同じくらい遠い情報源から遺伝情報を取り込むことさえできます。

すべての生物は何らかのゲノム(RNAやDNA)を持っていますが、これらの設計図のサイズにはかなりのばらつきがあります。1つの主要な...

Education

JoVE Core

Molecular Biology

分子生物学

Unit 1

ユニット1

DNA, Cells, and Evolution

DNA、細胞、そして進化

KEY TERMS AND CONCEPTS

主要用語と概念

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 分子生物学は、明確で簡潔なアニメーション ビデオ レッスンを通じて細胞の分子プロセスを紹介します。さらに、科学者の実際のビデオでは、これらの概念の応用が現代の研究室での実際の実験を通じて実証されています。

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

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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

Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and ...

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species&#x2014;groups of reproductively isolated populations.The ...

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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