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

Malgré la nature simple du code génétique, il y a une variation considérable en termes de taille génomique, entre le génome le plus petit connu, soit la protéobactérie Candidatus Carsonella ruddii qui a moins de 160 000 paires de base, au plus grand connu soit la plante à fleurs japonaise, le Paris japonica qui en a environ 150 milliards. Malgré ces extrêmes, en général les bactéries et archées ont environ 3, 000 gènes dans leurs génomes. Car les procaryotes n'ont presque aucunes séquences non-codantes, ce qui signifie que leurs génomes peuvent être relativement petits par rapport à ceux des eucaryotes.Un génome plus petit signifie également moins de réplicats à chaque tour de division cellulaire, ce qui fait sens logique pour une reproduction rapide. Typiquement, les eucaryotes ont aux environs de 20 000 gènes mais leurs génomes sont ponctués par de longues étendues de séquences non-codantes, ce qui signifie que la taille de leurs génomes n'est pas nécessairement liée à la complexité. Le génome du Paris japonica peut faire plus de 50 fois la taille du génome humain, mais cela est dû au moins en partie, à de grandes quantités de séquences non-codantes et probablement des niveaux élevés de duplication, et pas nécessairement plus de gènes nouveaux.Alors, comment les organismes peuvent-ils développer de nouveaux gènes Typiquement la réponse est en modifiant la séquence qui existe déjà. L'une des principales ressources pour l'apparition de nouveaux gènes est la duplication génétique. Imaginez une section d'ADN contenant un gène qui est accidentellement dupliqué.Maintenant, l'organisme a une deuxième copie d'un gène existant. Ces nouvelles copies de gènes sont exemptes des contraintes imposées à l'original pour maintenir la fonction de base. Et ainsi, elles peuvent diverger, potentiellement en développant un nouveau rôle ou en modifiant la fonction d'origine.Un autre moyen de créer de nouveaux gènes est la recombinaison aléatoire d'ADN où les segments d'un gène ou d'une copie de gène existant sont séparés et se déplacent pour rejoindre ceux d'un gène différent, créant ainsi un gène hybride qui peut assurer une nouvelle fonction. La mutation intragénique, changements dans une séquence génique introduits par des mutations au fil du temps, explique de nombreux nouveaux gènes. Cette divergence est la plus notable quand l'on compare des espèces ou lignées qui divergent indépendamment.Une fois que cette divergence va au-delà d'un certain point ou qu'un gène prend une nouvelle fonction. Ils peuvent être classés comme des gènes entièrement différents. Enfin, le transfert horizontal de gènes apporte de nouveaux gènes et de nouvelles séquences au génome depuis des sources externes, comme d'autres individus et même d'autres espèces.Ce type d'acquisition de nouveaux gènes est plus courant chez les procaryotes et les archées avec en exemple bien connu le transfert des gènes de résistance aux antibiotiques. Bien que rare chez les eucaryotes, il est toujours considéré comme une source essentielle de nouveauté génétique. Et le matériel génétique peut même venir d'espèces éloignées telles que les bactéries et les champignons, dans cet exemple.

taille du génome et évolution des nouveaux gènes

Bien que chaque organisme vivant possède un génome quelconque (qu’il s’agisse d’ARN ou d’ADN), il existe des variations considérables dans la taille de ces modèles. Un facteur majeur qui influe sur la taille du génome est de savoir si l’organisme est procaryote ou eucaryote. Chez les procaryotes, le génome contient peu ou pas de séquences non codantes, de sorte que les gènes sont étroitement rassemblés en groupes ou encore en opérons, de manière séquentielle le long du chromosome. À l’inverse, chez les eucaryotes, les gènes sont ponctués de longues séquences non codantes. Dans l’ensemble, cela contribue au phénomène selon lequel les génomes des procaryotes ont tendance à être plus petits (c’est-à-dire qu’il contient moins de bases) en moyenne que ceux des eucaryotes.

Sans surprise, compte tenu de cette observation, les plus petits génomes connus sont pour la plupart des procaryotes. Candidatus Carsonella ruddii, par exemple, est une protéobactérie hautement simplifiée dont le génome ne compte que 160 000 paires de bases. Ayant perdu de nombreux gènes nécessaires à la synthèse des protéines essentielles à la vie, il a évolué pour devenir un symbiote intracellulaire obligatoire. À l’opposé du spectre, la plante à fleurs eucaryote japonaise Paris japonica est l’un des plus grands génomes connus, avec environ 150 milliards de paires de bases. Bien que le nombre de gènes codés ne soit pas connu, le génome présente de grandes quantités de duplication et de séquences non codantes.

Dans le génome d’un procaryote moyen, il existe environ 3 000 gènes. L’eucaryote moyen en compte environ 20 000. Mais la taille du génome, en particulier chez les eucaryotes, est extrêmement variable – en grande partie à cause de la quantité de séquences non codantes.

La création de nouveaux gènes

Afin de faire évoluer de nouveaux gènes, les organismes disposent de quelques options principales. La plupart d’entre eux ont un point commun : ils modifient des séquences déjà existantes.

La duplication joue un rôle important dans la création de nouveaux gènes, et plusieurs types de duplication peuvent aboutir à ces nouvelles séquences. Lors de la duplication d'un gène, une section d'ADN contenant un gène est dupliquée. Cette seconde copie ne subit pas la pression de sélection qui contraint la première et peut donc diverger. Avec le temps, cela peut conduire à l’évolution de nouveaux gènes, dotés de nouveaux rôles.

Un autre type de duplication – le brassage d’ADN – peut entraîner la duplication d’une seule section d’un gène et sa jonction avec un autre gène. Cela peut aboutir à la création de nouveaux gènes, avec de nouveaux produits.

Parfois, de nouveaux gènes évoluent simplement à partir de mutations accumulées au fil du temps. Ceci est connu sous le nom de mutation intragénique et est particulièrement visible lors de comparaisons entre espèces ou populations divergentes.

Enfin, il est également possible d’obtenir de nouveaux gènes à partir de sources externes, selon un processus appelé transfert horizontal de gènes. Cela signifie que le matériel génétique peut être incorporé à partir d’autres individus, parfois de la même espèce, mais aussi potentiellement d’une autre espèce. Il s’agit d’une source fréquente de nouveaux gènes chez les procaryotes et les archées. C'est moins courant chez les eucaryotes, mais il a été démontré que cela se produit, et les eucaryotes peuvent même capter des informations génétiques provenant de sources aussi éloignées que des bactéries ou des champignons.

Taille du génome et évolution des nouveaux gènes

Bien que chaque organisme vivant ait un génome d’une sorte ou d’une autre (qu’il s’agisse d’ARN ou d’ADN), la taille de ces plans varie considérablement. Un ...

Education

Enseignement

JoVE Core

Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Cells, Genomes, and Evolution

Cellules, génomes et évolution

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 Biologie cellulaire illustre les processus cellulaires complexes dans des leçons vidéos complètes mais faciles à comprendre. Cette collection se concentre sur les composants et fonctions essentiels de la cellule ; cela inclut les organelles et les membranes ainsi que le transport et le métabolisme énergétique cellulaire. Elle est complétée par nos vidéos de scientifiques à l'action qui démontrent l'application de la biologie cellulaire dans des expériences concrètes.

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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