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

Trotz der einfachen Natur des genetischen Codes gibt es erhebliche Unterschiede in Bezug auf die Genomgröße, von den kleinsten bekannten Genomen - einschließlich des Proteobacteriums Candidatus Carsonella ruddii mit weniger als 160 Tausend Basenpaaren - bis hin zu den größten, wie der japanischen Blütenpflanze Paris japonica mit etwa 150 Milliarden><.
 
Trotz dieser Extreme haben Bakterien und Archaeen in der Regel rund 3.000 Gene in ihrem Genom. Da Prokaryoten fast keine nicht-kodierenden Sequenzen haben, bedeutet dies, dass ihre Genome im Vergleich zu denen von Eukaryoten relativ klein sein können. Kleinere Genome bedeuten auch, dass bei jeder Zellteilungsrunde weniger repliziert werden muss - was für eine schnelle Reproduktion logistisch sinnvoll ist.
Eukaryoten haben in der Regel etwa 20.000 Gene, aber ihre Genome sind von langen Abschnitten nicht-kodierender Sequenz durchzogen - was bedeutet, dass ihre Genomgröße nicht unbedingt zu Komplexität führt. 
Das Genom von Paris japonica mag mehr als fünfzigmal so groß sein wie das menschliche Genom - aber das ist zumindest teilweise auf große Mengen an nicht-kodierender Sequenz und wahrscheinlich ein hohes Maß an Duplikation zurückzuführen - nicht unbedingt auf neuere Gene.
Wie entwickeln Organismen also neue Gene? Die Antwort besteht in der Regel darin, die bereits vorhandene Sequenz zu ändern.
Eine der Hauptressourcen für die Evolution neuer Gene ist die Genduplikation. Stellen Sie sich vor, ein DNA-Abschnitt, der ein Gen enthält, wird versehentlich dupliziert. Nun besitzt der Organismus eine zweite Kopie eines vorhandenen Gens. 
Solche neuen Genkopien sind frei von den Zwängen, die dem Original auferlegt werden, um ihre Funktion aufrechtzuerhalten, und können daher divergieren - möglicherweise eine neue Rolle oder eine modifizierte Funktion des Originals entwickeln. 
Eine weitere Möglichkeit, neue Gene zu erzeugen, ist das DNA-Shuffling - bei dem Segmente eines vorhandenen Gens oder einer Genkopie getrennt und verschoben werden, um sich mit denen eines anderen Gens zu verbinden - wodurch ein Hybridgen entsteht, das eine neue Funktion übernehmen kann.
Intragene Mutation - die Veränderungen in einer Gensequenz, die durch Mutationen im Laufe der Zeit eingeführt werden, sind für viele "neue" Gene verantwortlich. Diese Divergenz macht sich am deutlichsten, wenn man Arten oder Abstammungslinien vergleicht, die ihrerseits unabhängig voneinander auseinanderdriften. Sobald diese Divergenz über einen bestimmten Punkt hinausgeht oder ein Gen eine neue Funktion übernimmt, können sie als völlig unterschiedliche Gene klassifiziert werden.
Schließlich bringt der horizontale Gentransfer neue Gene und Sequenzen aus externen Quellen in das Genom ein - wie andere Individuen und sogar andere Arten. Diese Art der neuartigen Genakquisition ist am häufigsten bei Prokaryoten und Archaeen, wobei der Transfer von Antibiotikaresistenzgenen ein bekanntes Beispiel ist. 
Obwohl es bei Eukaryoten selten ist, gilt es immer noch als wesentliche Quelle für genetische Neuheit, und genetisches Material kann sogar von entfernt verwandten Arten stammen, wie in diesem Beispiel die Bakterien und Pilze.

genomgröße und die entwicklung neuer gene

Obwohl jeder lebende Organismus über ein Genom verfügt (sei es RNA oder DNA), gibt es erhebliche Unterschiede in der Größe dieser Baupläne. Ein wichtiger Faktor, der die Genomgröße beeinflusst, ist, ob der Organismus prokaryotisch oder eukaryotisch ist. Bei Prokaryoten enthält das Genom nur wenige bis gar keine nichtkodierenden Sequenzen, sodass die Gene eng in Gruppen oder Operonen nacheinander entlang des Chromosoms geclustert sind. Umgekehrt sind die Gene in Eukaryoten durch lange Abschnitte nichtkodierender Sequenzen unterbrochen. Insgesamt trägt dies zu dem Phänomen bei, dass prokaryotische Genome im Durchschnitt tendenziell kleiner sind (d.h. weniger Basen enthalten) als die von Eukaryoten.

Angesichts dieser Beobachtung überrascht es nicht, dass die kleinsten bekannten Genome größtenteils Prokaryoten sind. Candidatus Carsonella rudii beispielsweise ist ein stark vereinfachtes Proteobakterium mit einer Genomgröße von nur 160.000 Basenpaaren. Da es viele Gene verloren hat, die es für die Synthese lebenswichtiger Proteine benötigte, hat es sich zu einem obligaten intrazellulären Symbionten entwickelt. Am anderen Ende des Spektrums ist die eukaryotische japanische Blütenpflanze Paris japonica mit rund 150 Milliarden Basenpaaren eines der größten bekannten Genome. Obwohl die Anzahl der Gene, die dadurch kodiert werden, nicht bekannt ist, weist das Genom große Mengen an Duplikationen und nichtkodierenden Sequenzen auf.

Im Genom eines durchschnittlichen Prokaryoten gibt es etwa 3.000 Gene. Der durchschnittliche Eukaryote hat etwa 20.000. Aber die Genomgröße, insbesondere bei Eukaryoten, ist sehr unterschiedlich – was zum großen Teil auf die Menge an nichtkodierenden Sequenzen zurückzuführen ist.

Die Schaffung neuer Gene

Um neue Gene zu entwickeln, haben Organismen einige Hauptoptionen. Den meisten davon ist gemeinsam, dass sie bereits vorhandene Sequenzen modifizieren.

Die Duplikation spielt eine wichtige Rolle bei der Entstehung neuer Gene, und es gibt einige Arten der Duplikation, die zu diesen neuartigen Sequenzen führen können. Bei der Genduplikation wird ein DNA-Abschnitt dupliziert, der ein Gen enthält. Diese zweite Kopie unterliegt nicht dem Selektionsdruck, der die erste einschränkt, und kann daher abweichen. Mit der Zeit kann dies zur Entwicklung neuer Gene mit neuen Rollen führen.

Eine andere Art der Duplikation – das DNA-Shuffling – kann dazu führen, dass nur ein Abschnitt eines Gens dupliziert wird und mit einem anderen Gen verbunden wird. Dies kann zur Entstehung neuartiger Gene und neuartiger Produkte führen.

Manchmal entstehen im Laufe der Zeit neue Gene einfach aus akkumulierten Mutationen. Dies wird als intragene Mutation bezeichnet und macht sich am deutlichsten beim Vergleich verschiedener Arten oder unterschiedlicher Populationen bemerkbar.

Schließlich ist es auch möglich, neue Gene aus externen Quellen zu gewinnen, ein Prozess, der als horizontaler Gentransfer bezeichnet wird. Dies bedeutet, dass genetisches Material von anderen Individuen übernommen werden kann, manchmal von derselben Art, möglicherweise aber auch von einer völlig anderen Art. Dies ist eine häufige Quelle neuer Gene in Prokaryoten und Archaeen. Es kommt bei Eukaryoten weniger häufig vor, kommt aber nachweislich vor, und Eukaryoten können sogar genetische Informationen aus so weit entfernten Quellen wie Bakterien oder Pilzen aufnehmen.

Genomgröße und die Entwicklung neuer Gene

Während jeder lebende Organismus irgendeine Art von Genom hat (sei es RNA oder DNA), gibt es erhebliche Unterschiede in der Größe dieser Baupläne. Ein wichtiger ...

Education

Lehre

JoVE Core

Molecular Biology

Molekularbiologie

Unit 1

Einheit 1

DNA, Cells, and Evolution

DNA, Zellen und Evolution

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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 veranschaulicht die molekularen Prozesse der Zelle in prägnanten animierten Video-Lektionen. In Videos von Wissenschaftlern in Aktion wird die Anwendung dieser Konzepte zusätzlich durch reale Experimente in modernen Laboren demonstriert.

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

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Speciation Rates

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Genetics of Speciation

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Hybrid Zones

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What is Natural Selection?

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

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Artificial Selection

Natural Selection and Adaptive Evolution
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Observing Artificial Selection in Plants
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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

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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 ...

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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

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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 ...

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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 ...

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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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