Name: genome size and gene evolution
Uploaded: 2023-04-30T18:28:42.000Z
Duration: 3 min 21 s
Channel: JoVE

K12 Standards

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

North Carolina K-12 Science Standard Course of Study

9-12

Biology

heredity-inheritance-and-variation-of-traits

Heredity- Inheritance and Variation of Traits

LS.Bio.6.2

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 evolution 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 Evolution 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

Cell Biology

Zellbiologie

Unit 1

Einheit 1

Cells, Genomes, and Evolution

Zellen, Genome und Evolution

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

genome size and gene evolution

Genome size and gene evolution are linked through changes in DNA sequence and genome structure. Some genes can arise from parts of the genome that were not coding before, while others come from changes to existing genes. These shifts help explain how new genetic material can appear over time.

A genome is the full set of DNA in an organism. Its size can change as DNA is added, removed, or rearranged. The transcript highlights that genome size is not fixed, and that these changes can shape the evolution of new genes.

New genes may form by duplication and later change, or by other alterations in noncoding DNA. Over time, these changes can give rise to new functions. This process helps connect genome structure with the emergence of genetic novelty.

Genome Size and Gene Evolution

what are cells?

Cells as the Building Blocks of Life

Cells are the basic building blocks of life. A bacterium can be a single cell, while a human is made of trillions of cells. Even with this range, cells share key features that support life. A living cell has a plasma membrane. This is a bilayer of lipids that separates the cytoplasm inside the cell from the outside environment. A cell also carries genetic information in the form of DNA. In prokaryotic cells, DNA is found in a region called the nucleoid. In eukaryotic cells, DNA is enclosed...

the tree of life - bacteria, archaea, and eukaryotes

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

Three Domains on the Tree of Life

The tree of life shows how living things are grouped into three domains: Bacteria, Archaea, and Eukaryotes. This classification helps explain the major branches of life and how they are related. Bacteria and Archaea are both single-celled organisms, but they are not the same. Eukaryotes include organisms with more complex cells, such as plants, animals, and fungi. Together, these three domains give a broad picture of life on Earth. Understanding the tree of life helps students compare cell...

prokaryotic cells

How Prokaryotes Survive Without a Nucleus

Prokaryotes are small unicellular organisms that live without a nucleus. They include the domains Archaea and Bacteria. Bacteria include common microbes such as Salmonella and E. coli, while Archaea include extremophiles that live in harsh places like volcanic springs. Prokaryotic cells still share several basic features with eukaryotic cells. They have a plasma membrane, cytoplasm, ribosomes, and genetic material in the form of single, circular DNA. Their cell parts float freely in the...

eukaryotic compartmentalization

How Organelles Keep Cells Working

Eukaryotic cells keep their organelles separate so each part can do a specific job. Organelles such as the nucleus and mitochondria are surrounded by membranes. These membranes are selectively permeable, which means they control what enters and leaves. That control creates small internal environments with conditions suited to each organelle. These controlled spaces help organelles work more efficiently. In animal cells, lysosomes keep an acidic environment that helps their enzymes digest...

eukaryotic evolution

How Eukaryotic Cells Became Complex

Eukaryotic cells became complex through a debated evolutionary path that likely involved endosymbiosis. The most accepted model is the endosymbiont theory, which explains how organelles such as mitochondria and chloroplasts may have entered an ancestral cell. Other ideas include the nucleus-first hypothesis, the mitochondria-first hypothesis, and the eukaryote-first hypothesis. The nucleus-first hypothesis says an ancestral prokaryote first formed a membrane around its DNA, creating the...

animal and plant cell structure

Plant vs Animal Cell Division and Specialization

Plant and animal cells differ in how they divide, organize into tissues, and specialize for different jobs. Both cell types divide by mitosis in non-gametic cells and by meiosis in gametic cells, but the details are not the same. These differences help explain how each cell type supports growth and reproduction. During cell division, animal cells use centrosomes to organize spindle fibers and separate chromosomes. Plant cells do not have centrosomes. Instead, they use a microtubule-organizing...

cytoplasm

Cytoplasm and the Cell’s Internal Support

The cytoplasm is the cell’s internal space that holds organelles and the cytoskeleton. It is suspended in the cytosol, an aqueous fluid made of water, ions, salts, and many organic molecules. This fluid helps keep the cell organized and supports many cellular activities. The cytoplasm is also where protein synthesis and protein folding take place. The watery cytosol helps proteins fold correctly. In a folded protein, hydrophobic amino acid side chains tend to stay buried in the core, while...

the nucleus

Nuclear DNA, Chromatin, and Nucleoli

The nucleus is a membrane-bound organelle that stores chromosomal DNA and helps control what proteins a eukaryotic cell makes. It acts as the cell’s control center. DNA in mitochondria and chloroplasts is different because it mainly supports functions specific to those organelles. Inside the nucleus, DNA is wrapped around proteins called histones. This DNA-protein complex is called chromatin. During interphase, when the cell is not dividing, chromatin stays loosely arranged so the DNA is easy...

the dna helix

How DNA Structure Was Discovered

DNA is the genetic material that passes traits from one generation to the next in organisms and most viruses. It is made of two strands of nucleotides that twist into a spring-like double helix. The shape is not perfectly even. It also has repeating grooves called the major groove and the minor groove. The major groove forms where the sugar-phosphate backbones are farther apart. This wider space gives DNA-binding proteins, including transcription factors, better access to the bases. The minor...

the central dogma

DNA to Protein: RNA’s Role

DNA to protein flow depends on RNA as the link between genetic information and the amino acids that build proteins. Early scientists knew that DNA stores the information for cell functions and that proteins carry out most of those functions. For a long time, they did not know how the code in DNA became a working protein. At first, many people thought one gene was changed directly into its protein. Two findings in eukaryotic cells challenged that idea. Protein production does not happen in the...

mutations

Mutations in DNA and Inherited Disease

Mutations are changes in the DNA sequence. They can happen on their own during DNA copying, or they can be caused by environmental factors. Scientists describe mutations in several ways, including whether they change the amino acid sequence of a protein, how much DNA they affect, and whether they occur in somatic cells or germline cells. Some mutations are point mutations. A point mutation changes a single nucleotide in DNA. Other mutations are chromosomal alterations, which change the number...

genome size and the evolution of new genes

Genome size and gene evolution are linked through changes in DNA sequence and genome structure. Some genes can arise from parts of the genome that were not coding before, while others come from changes to existing genes. These shifts help explain how new genetic material can appear over time. A genome is the full set of DNA in an organism. Its size can change as DNA is added, removed, or rearranged. The transcript highlights that genome size is not fixed, and that these changes can shape the...

gene families

Shared Origins of Gene Families

Gene families are groups of related genes that share a common origin. They form when genes are copied and then change over time. These related genes can be found within the same genome. The video also connects gene families to homologous genes and orthologous genes. Homologous genes are genes with a shared evolutionary origin. Orthologous genes are homologous genes found in different species. Gene families help show how these relationships are used to study evolution and related gene functions.

gene evolution - fast or slow?

Gene Evolution Rates and Selection

Gene evolution can happen at different rates, and natural selection helps shape those changes. Some genes change slowly because important DNA changes are removed over time. Other genes can change more quickly when different mutations are kept in a population. The rate of evolution depends on how a gene is used and how strongly it is affected by selection. Genes with essential jobs often stay more similar across species. Genes under weaker pressure may show more variation and may evolve faster.<br...

types of genetic transfer between organisms

types-of-genetic-transfer-between-organisms

Vertical and Horizontal Gene Transfer

Genetic transfer between organisms happens in two main ways: vertical gene transfer and horizontal gene transfer. These two routes explain how hereditary material moves from one generation to the next or between organisms that are not parent and offspring. Vertical gene transfer passes genes from parent to offspring during reproduction. This is the usual way genetic information is inherited in living things. Horizontal gene transfer moves genetic material between organisms outside of...

key terms and concepts

Explore how genome size changes can shape gene evolution, including gene duplication, DNA rearrangement, and the rise of new genetic functions.

Genome Size and Gene Evolution | JoVE K12

cell biology

JoVE Core Zellbiologie veranschaulicht komplexe zelluläre Prozesse in leicht verständlichen und dennoch umfassenden animierten Videolektionen. Diese Sammlung konzentriert sich auf die wesentlichen Bestandteile und Funktionen von Zellen, einschließlich Organellen und Membranen, Zelltransport und Zellenergie. Ergänzt wird sie durch Videos von Wissenschaftlern in Aktion, die die Anwendung der Zellbiologie in realen Forschungsexperimenten demonstrieren.

Pennsylvania State Academic Standards

Life Science

Inheritance and Variation of Traits

3.1.9-12.P

3.1.9-12.Q

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Heredity

Mutations

Virginia  Standards of Learning

HIgh School

BIO.5

BIO.5.b

Arizona Science Standards

HS.L3

HS.L3U1.25

HS+B.L3

HS+B.L3U1.12

Next Generation Science Standards

Heredity: Inheritance and Variation of Traits

HS-LS3-2

new-york-state-science-learning-standards

New York State Science Learning Standards

HS-LS3-1.

What is Meiosis?

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from ...

Meiosis I

Meiosis II

Meiosis vs. Mitosis

Crossing Over

Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to ...

Nondisjunction

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This ...

Spermatogenesis

Spermatogenesis is the process by which haploid sperm cells are produced in the male testes. It starts with stem cells located close to the outer rim of ...

Oogenesis

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from ...

Fertilization

During fertilization, an egg and sperm cell fuse to create a new diploid structure. In humans, the process occurs once the egg has been released from the ...

Cleavage and Blastulation

After a large-single-celled zygote is produced via fertilization, the process of cleavage occurs while zygotes travel through the uterine tube. Cleavage ...

Gastrulation

Gastrulation establishes the three primary tissues of an embryo: the ectoderm, mesoderm, and endoderm. This developmental process relies on a series of ...

Neurulation

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three ...

Cell Migration

Cell migration, the process by which cells move from one location to another, is essential for the proper development and viability of organisms ...

Determination

During embryogenesis, cells become progressively committed to different fates through a two-step process: specification followed by determination. ...

Use models to explain how DNA is passed from parents to offspring through the processes of meiosis and fertilization in sexual reproduction.

LS.Bio.6.1

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations ...

Types of Genetic Transfer Between Organisms

Base-pairing and DNA Repair

The DNA Replication Fork

Lagging Strand Synthesis

The Replisome

Proofreading

Synthesis of new DNA molecules is carried out by the enzyme DNA polymerase, which adds nucleotides on the daughter strand complementary to the template ...

Replication in Prokaryotes

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to the ...

Replication in Eukaryotes

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before ...

Overview of DNA Repair

Base Excision Repair

Nucleotide Excision Repair

DNA Distortion and Damage
Cells are regularly exposed to mutagens&#8212;factors in the environment that can damage DNA and generate mutations. UV ...

Mismatch Repair

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the ...

Fixing Double-strand Breaks

Homologous Recombination

Gene Conversion

Restarting Stalled Replication Forks

Construct an explanation to summarize how inheritable genetic variations may result from: new genetic combinations in meiosis, mutations during replication, or mutations caused by environmental factors.

An Overview of Genetic Analysis

An organism&#8217;s physical traits, or phenotype, are a product of its genotype, which is the combination of alleles (gene variants) inherited from its ...

Genetic Crosses

To dissect genetic processes or create organisms with novel suites of traits, scientists can perform genetic crosses, or the purposeful mating of two ...

Punnett Squares

Monohybrid Crosses

Dihybrid Crosses

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel&#8217;s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A ...

Law of Independent Assortment

Chi-square Analysis

The chi-square test is a statistical hypothesis test. It is used to check whether there is a significant difference between an expected value and an ...

Pedigree Analysis

Multiple Allele Traits

Incomplete Dominance

Gregor Mendel&#39;s work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid ...

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cu&#233;not discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is ...

Polygenic Traits

background-and-environment-affect-phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as ...

Use mathematics and computational thinking to predict the variation and distribution of expressed traits based on: Mendelian inheritance, co-dominance, incomplete dominance, multiple alleles, and sex-linked inheritance.

LS.Bio.7.1

Overview

A pedigree is a diagram displaying a family&#x2019;s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or ...

Probability Laws

Overview

The probability of inheriting a trait can be calculated using the sum and product rules. The sum rule is used to calculate the probability of ...

The Concept of Multiple Allelism

Multiple allelism describes genes that exist in three or more allelic forms. Although diploid organisms, like humans, ...

Analyze and interpret data to explain how polygenic traits result in a wide range of phenotypes.

LS.Bio.7.2

Pleiotropy

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause ...

Nature and Nurture

Many human characteristics, like height, are shaped by both nature&mdash;in other words, by our genes&mdash;and by nurture, or our environment. For ...

Construct an explanation to summarize how traits result from interactions of genetic factors (multiple genes and/or alleles) and environmental factors.

LS.Bio.7.3

PCR: The Polymerase Chain Reaction

The polymerase chain reaction, or PCR, is a technique used to amplify DNA through thermocycling &#8211; cyles of temperature changes at fixed time ...

DNA Gel Electrophoresis

DNA gel electrophoresis is a technique used for the detection and separation of DNA molecules. An electric field is applied to a gel matrix comprised of ...

DNA Isolation

DNA isolation protocols can be fast and straightforward or complex and time-consuming depending on the type and quality of DNA required for further ...

Analyze and interpret data to compare DNA samples.

LS.Bio.8.1

Understand genetic mechanisms for variation.

Genome Size and Gene Evolution

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