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

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

Cell Biology

細胞生物学

Unit 1

ユニット1

Cells, Genomes, and Evolution

細胞、ゲノム、そして進化

KEY TERMS AND CONCEPTS

主要用語と概念

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 細胞生物学は、複雑な細胞プロセスを、わかりやすく包括的なアニメーション ビデオ レッスンで説明します。このコレクションは、細胞小器官や膜、細胞輸送、細胞のエネルギー学など、細胞の必須コンポーネントと機能に焦点を当てています。これは、実際の研究実験における細胞生物学の応用を実証する科学者による実際のビデオによって補足されています。

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 ...

Restriction Enzymes

Restriction enzymes are bacterial enzymes used to cut DNA in a sequence-specific manner. To cleave DNA, they bind to specific palindromic sequences called ...

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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