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

Nonostante la semplice natura del codice genetico, c'è una notevole variazione in termini di dimensione del genoma, dai genomi più piccoli conosciuti, come il 00:00:10.910 00:00:13.670 proteobatterio candidatus Carsonella ruddii a meno di 160.000 paia di basi, ai più grandi come il fiore Paris japonica a circa 150 miliardi. Estremi a parte, i batteri e gli archea hanno generalmente circa 3, 000 geni all'interno dei loro genomi. I procarioti quasi non possiedono sequenze non codificanti, ciò significa che i loro genomi possono essere relativamente piccoli rispetto a quelli degli eucarioti.Genoma più piccolo significa anche minore capacità di replicare ad ogni ciclo della divisione cellulare, che da senso logico alla riproduzione più veloce. Gli eucarioti hanno tipicamente regioni di 20, 000 geni, ma i loro genomi sono punteggiati da lunghi tratti di sequenza non codificante, il che significa che la loro dimensione di genoma non necessariamente ne traduce la complessità. 00:01>00.01 07.820 Il genoma del fiore Paris japonica può essere oltre 50 volte la dimensione del genoma umano, ma ciò è dovuto almeno in parte a grandi quantità di sequenza non codificante 00:01:17.520 00:01:20.270 e probabilmente alti livelli di duplicazione, non necessariamente per nuovi geni.Allora, come gli organismi creano nuovi geni? La risposta è in genere modificando la sequenza che già esistente. Una delle risorse primarie dei i nuovi geni per evolvere è attraverso la duplicazione dei geni.Immaginate che una sezione di DNA contenente un gene venga accidentalmente duplicato. L'organismo avrà una seconda copia di un gene già esistente. Tali nuove copie geniche sono esenti dai vincoli posti all'originale per mantenere la sua funzione.Le due copie possono quindi potenzialmente divergere creando un nuovo ruolo o modificando la funzione originale. Un altro modo per creare nuovi geni è il DNA shuffling, dove segmenti di un gene esistente o copia del gene sono separati e si spostano per unire quelli di un gene diverso, 00:02:11.610 00:02:16.500 creando un gene ibrido che può assumere una nuova funzione. La mutazione intragenica, i cambiamenti in una sequenza genica indotti dalle mutazioni nel tempo, rappresenta molti nuovi geni.Questa divergenza è più evidente quando si confrontano specie o linee che divergono indipendentemente. Una volta che questa divergenza è oltre un certo punto o che un gene assume una nuova funzione, possono essere classificati interamente come geni diversi. Infine, il trasferimento genico orizzontale porta in nuovi geni e nuove sequenze al genoma da fonti esterne, da altri individui e anche da altre specie.Questo tipo di acquisizione di nuovi geni è più comune nei procarioti e negli archea con il trasferimento di geni di resistenza agli antibiotici come esempio ben noto;metre è raro negli eucarioti, è ancora considerato una fonte essenziale di novità genetiche. Il materiale genetico può anche derivare da specie non correlate, come i batteri e funghi in questo esempio.

dimensione del genoma ed evoluzione di nuovi geni

Sebbene ogni organismo vivente abbia un genoma di qualche tipo (sia esso RNA o DNA), esiste una notevole variazione nelle dimensioni di questi. Uno dei fattori principali che influisce sulla dimensione del genoma è se l’organismo è procariotico o eucariotico. Nei procarioti, il genoma contiene poche o zero sequenze non codificanti, quindi i geni sono strettamente raggruppati in gruppi o operoni in sequenza lungo il cromosoma. Al contrario, i geni negli eucarioti sono punteggiati da lunghi tratti di sequenze non codificanti. Nel complesso, ciò contribuisce al fenomeno per cui, in media, i genomi procariotici tendono ad essere più piccoli (cioè contengono meno basi) rispetto a quelli degli eucarioti.

Non sorprende, data questa osservazione, che i genomi più piccoli conosciuti siano per lo più procarioti. Il Candidatus Carsonella rudii, ad esempio, è un proteobatterio altamente semplificato che ha una dimensione del genoma di appena 160mila paia di basi. Avendo perso molti geni necessari per sintetizzare proteine essenziali per la vita, si è evoluto fino a diventare un simbionte intracellulare obbligato. All'estremità opposta dello spettro, la pianta eucariota giapponese Paris japonica è uno dei genomi più grandi conosciuti, con circa 150 miliardi di coppie di basi. Sebbene il numero di geni che questo codifica non sia noto, il genoma mostra grandi quantità di duplicazioni e sequenze non codificanti.

Nel genoma di un procariota medio ci sono circa 3.000 geni. L'eucariota medio ne conta circa 20.000. Ma la dimensione del genoma, soprattutto negli eucarioti, è estremamente variabile, in gran parte a causa della quantità di sequenze non codificanti.

La Creazione di Nuovi Geni

Per evolvere nuovi geni, gli organismi hanno a disposizione alcune opzioni principali. L'unica cosa che la maggior parte di questi ha in comune è che modificano sequenze già esistenti.

La duplicazione gioca un ruolo importante nella creazione di nuovi geni e ci sono alcuni tipi di duplicazione che possono dare come risultato queste nuove sequenze. Nella duplicazione genica, viene duplicata una sezione di DNA contenente un gene. Questa seconda copia non subisce la pressione selettiva che vincola la prima e quindi può divergere. Col tempo, ciò può portare all’evoluzione di nuovi geni, con nuovi ruoli.

Un altro tipo di duplicazione, il mescolamento del DNA, può far sì che solo una sezione di un gene venga duplicata e si unisca a un altro gene. Ciò può portare alla creazione di nuovi geni, con nuovi prodotti.

A volte i nuovi geni si evolvono semplicemente da mutazioni accumulate nel tempo. Questo fenomeno è noto come mutazione intragenica ed è più evidente quando si confrontano specie o popolazioni divergenti.

Infine, è anche possibile ottenere nuovi geni da fonti esterne, in un processo noto come trasferimento genico orizzontale. Ciò significa che il materiale genetico può essere incorporato da altri individui, talvolta della stessa specie, ma potenzialmente anche da una specie completamente diversa. Questa è una fonte causa frequente nella creazione di nuovi geni nei procarioti e negli archaeaarchei. È meno comune negli eucarioti, ma è stato dimostrato che può verificarsi e gli eucarioti possono persino raccogliere informazioni genetiche da fonti distanti, come batteri o funghi.

Dimensione del Genoma ed Evoluzione di Nuovi Geni

Mentre ogni organismo vivente ha un genoma di qualche tipo (che si tratti di RNA o DNA), c'è una notevole variazione nelle dimensioni di questi progetti. Uno dei principali ...

Education

Didattica

JoVE Core

Molecular Biology

Biologia Molecolare

Unit 1

Unità 1

DNA, Cells, and Evolution

DNA, cellule ed evoluzione

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

Le video animazioni di JoVE Core Molecular Biology, organizzate in video lezioni, illustrano i processi molecolari cellulari in maniera chiara e concisa. Inoltre, nei video di "scienziati in azione", i concetti scientifici vengono applicati e dimostrati da ricercatori attraverso esperimenti in laboratorio.

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

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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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Types of Selection

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Frequency-dependent Selection

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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 ...

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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
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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 ...

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Changes in the environment of the early Earth drove the evolution of organisms. As prokaryotic organisms in the oceans began to photosynthesize, they ...

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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 ...

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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

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 ...

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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 ...

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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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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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