Name: gene evolution rates and selection
Uploaded: 2023-04-30T18:28:42.000Z
Duration: 2 min 5 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Life Science

Inheritance and Variation of Traits

3.1.9-12.Q

Gene Evolution - Fast or Slow?

האופן שבו מוטציות משפיעות על הישרדותו של תא תלוי במידה רבה במיקום השינוי הגנטי. באזורים בגנום שאינם מקודדים גנים או אזורי בקרה למוטציות עשויה להיות השפעה מועטה, כך שהתא יכול לעתים קרובות להמשיך כרגיל.
ההשפעה הכוללת היא שרצפים שאינם מקודדים חופשיים להשתנות די מהר במונחים אבולוציוניים, כלומר אזורים אלה של גנום עשויים להיות כמעט בלתי ניתנים לזיהוי אפילו בשני מינים קרובים.
עם זאת, ברצפי קידוד, מוטציות אינן מאומצות באופן חופשי כל כך. בעוד שבמקרים נדירים מאוד הם עשויים להועיל, כגון מוטציה בגן לאנזים היוצרת זיקה קושרת טובה יותר לסובסטרט; הרוב יהיה מזיק.
בואו נסתכל על הגן rRNA 16s, למשל. הוא מקודד רנ"א מבני המהווה חלק מהריבוזום. חלק מהאזורים של רנ"א זה קריטיים לתפקוד הריבוזום, ושינויים במקטעים אלה נדירים במיוחד. האזורים האלה שהשתמרו מאוד משתנים לאט כל כך, שאפשר להשתמש בהם כדי לבחון הומולוגיה של רצפים בין פילות, ממלכות ואפילו כל המינים החיים – מה שהופך אותם לכלי רב ערך לחקר יחסים בין אורגניזמים קרובים זה לזה.
עם זאת, ישנם עדיין חלקים ברצף ה-rRNA של 16s פחות קריטיים לתפקוד, אשר עשויים להתפתח מעט מהר יותר. "אזורים משתנים" אלה יכולים להיות שימושיים להבהרת יחסים בין מינים קרובים יותר – כגון סוגים או אפילו זנים של חיידקים.
בסך הכל, זה מוביל לתופעה שאזורי גנום שונים עשויים להתפתח בקצב שונה בהרבה, אפילו בתוך אזורים המקודדים גן יחיד.

אבולוציה גנטית - מהירה או איטית?

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הגנום של האאוקריוטים מנוקד על ידי רצף ארוך שאינו מקודד לחלבונים או RNA. למרות שחלק מהאזורים הללו מכילים רצפים רגולטוריים מכריעים, הרוב המכריע של ה-DNA הזה אינו ממלא תפקיד ידוע. בדרך כלל, אזורים אלה של הגנום הם אלה שבהם נצפה השינוי המהיר ביותר, במונחים אבולוציוניים, מכיוון שבדרך כלל יש לחץ ברירה מועט או לא הפועל על אזורים אלה כדי לשמר את הרצפים שלהם.

לעומת זאת, אזורים המקודדים לחלבון עלולים לחוות לחץ בחירה גבוה, מכיוון שכל שינוי ברצף שלהם עלול לגרום לחלבון שפחות מסוגל לבצע את תפקידו בצורה מיטבית. עם זאת, מדי פעם מוטציה באחד מהאזורים הללו תגרום לתוצאה מועילה שתורמת לכושרו הכללי של האורגניזם, ומוטציות כאלה לרוב נמשכות ואף עשויות להתקבע באוכלוסיות. כאשר משווים את תדירות אירועי המוטציה הללו לשינויים הקבועים יחסית הנראים ברצפים שאינם מקודדים, הדבר נדיר ביותר, ולכן באופן כללי אזורי קידוד נחשבים כמתפתחים לאט.

זה גם נכון שיש כמות ניתנת למדידה של שונות ברמות שימור הרצף בתוך רצפי קידוד, וזה נראה על פני כל האורגניזמים. לדוגמה, קח את הדוגמה של חלבון קולטן. לחלבונים כאלה יש בדרך כלל אזורים שונים שעשויים לבצע פונקציות כמו קישור ליגנד, או איתות תוך תאי, או אינטגרציה של ממברנות. במקרה זה, מוטציה באזור המעורבת בקישור הליגנד עשויה לייצר חלבון שפחות יעיל בקשירת הליגנד. לכן, סביר להניח שלחץ הבחירה יהיה גבוה על הנוקלאוטידים המסוימים המקודדים לחלק זה של החלבון. עם זאת, בקטע של החלבון שמתפרש על פני הממברנה, ייתכן שתראה פחות השפעה אם מתרחשת החלפת חומצות אמינו, ולכן רמות נמוכות יותר של לחץ בחירה. בתנאים אלה, אנו עשויים לראות שלשני אזורים של אותו גן מקודד חלבון עשויים להיות קצבי התפתחות שונים.

רצף גנים או אזורים גנומיים לבניית פילוגניות

ניתן לחקור את השונות הזו במהירות התפתחות הגנום על פני אזורים שונים כדי לענות על שאלות על יחסים אבולוציוניים. ניתן לבחור גנים ואזורי גנים ולרצף אותם על פני קבוצות של פרטים כדי לענות על שאלות צרות כמו "האם אוכלוסיות אלו עשויות להיות מינים שונים?" או רחבה כמו "כיצד הפילות הללו ממוקמות בעץ החיים?". עבור הראשונים, בחירת גן שיש לו אזור משומר קל יחסית תעזור לזהות הבדלים ברמת האוכלוסייה. לעומת זאת, כדי לענות על שאלות על קבוצות מגוונות כמו פילה, אזור גן שמור מאוד עשוי לספק מספיק הומולוגיה כדי לייצר פילוגניה של קבוצות כאלה. אזורים בשימוש נפוץ עבור ניתוחים פילוגנטיים מולקולריים כגון אלה כוללים גנים ריבוזומליים של rRNA (כגון 16s rRNA, 18s rRNA או 28s rRNA), או אזורים גנומיים הידועים בשם ITS (Internal Transcribed Spacers, I או II) היושבים בין תת-יחידת ה-rRNA הריבוזומלית גנים.
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הגנום של האיקריוטים מנוקד על ידי רצפים ארוכים שאינם מקודדים חלבונים או רנ"א. למרות שחלק מאזורים אלה מכילים ...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Cells, Genomes, and Evolution

תאים, גנומים ואבולוציה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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.

Comparing gene sequences helps scientists see these patterns over time. These comparisons can show which regions are conserved and which regions have changed more rapidly. That information helps explain how genes evolve in different lineages.

Gene Evolution Rates and Selection

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-the-evolution-of-new-genes

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...

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 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 natural selection affects gene evolution rates, from slowly changing conserved genes to faster-changing genes with more variation.

Gene Evolution Rates and Selection | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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

Biology

Heredity

Mutations

Virginia  Standards of Learning

HIgh School

BIO.5

BIO.5.b

Next Generation Science Standards

heredity-inheritance-and-variation-of-traits

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 the Cell Cycle?

The cell cycle refers to the sequence of events occurring throughout a typical cell&#8217;s life. In eukaryotic cells, the somatic cell cycle has two ...

Interphase

The cell cycle occurs over approximately 24 hours (in a typical human cell) and in two distinct stages: interphase, which includes three phases of the ...

The Cell Cycle Control System

Positive Regulator Molecules

Inhibition of CDK Activity

Mitosis and Cytokinesis

In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome ...

Chromosome Duplication

Cohesins

Condensins

The Mitotic Spindle

Centrosome Duplication

Spindle Assembly

Attachment of Sister Chromatids

Forces Acting on Chromosomes

Separation of Sister Chromatids

The Spindle Assembly Checkpoint

Anaphase A and B

Anaphase Promoting Complex

The Contractile Ring

Determining the Plane of Cell Division

The Phragmoplast

Distribution of Cytoplasmic Content

An Introduction to Cell Division

Cell division is the process by which a parent cell divides and gives rise to two or more daughter cells. It is a means of reproduction for single-cell ...

Cell Cycle Analysis

Cell cycle refers to the set of events through which a cell grows, replicates its genome, and ultimately divides into two daughter cells through the ...

Live Cell Imaging of Mitosis

Mitosis is a form of cell division in which a cell&#8217;s genetic material is divided equally between two daughter cells. Mitosis can be broken down into ...

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 ...

an-introduction-to-developmental-genetics

An Introduction to Developmental Genetics

Development is the complex process through which a single-celled embryo transforms into a multicellular organism. Developmental processes are guided by ...

An Introduction to Organogenesis

Organogenesis is the process by which organs arise from one of three germ layers during the later stages of embryonic development. Researchers studying ...

Fate Mapping

Fate mapping is a technique used to understand how embryonic cells divide, differentiate, and migrate during development. In classic fate mapping ...

Students who demonstrate understanding can use a model to illustrate the role of cellular division (mitosis) and differentiation in producing and maintaining complex organisms.  Assessment Boundary: Assessment does not include specific gene control mechanisms or rote memorization of the steps of mitosis.

3.1.9-12.D

DNA Packaging

DNA as a Genetic Template

Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The ...

Organization of Genes

Structure of a Gene

A gene is the fundamental unit of heredity. Every individual has two copies of each gene, one inherited from each parent. Although most people contain the ...

Chromosome Structure

A functional eukaryotic chromosome must contain three elements: a centromere, telomeres, and numerous origins of replication.
The centromere is a DNA ...

Chromosome Replication

Before a cell can divide, it must accurately replicate all of its chromosomes, including the DNA and its associated histone and non-histone ...

The Nucleosome

DNA in a human cell is almost 2m long and it is packed inside a tiny nucleus that is only a few microns in diameter. The level of compaction of DNA inside ...

The Nucleosome Core Particle

Nucleosomes are the DNA-histone complex, where the DNA strand is wound around the histone core. The histone core is an octamer containing two copies of ...

Nucleosome Remodeling

Nucleosomes are the basic units of chromatin compaction. Each nucleosome consists of the DNA bound tightly around a histone core, which makes the DNA ...

Chromatin Packaging

Each human somatic cell contains 6 billion base-pairs of DNA. Each base-pair is 0.34 nm long, which means that each diploid cell contains a staggering 2 ...

Karyotyping

Proteins: From Genes to Degradation

The DNA Helix

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most viruses. DNA ...

The Central Dogma

The central dogma explains the flow of genetic information from DNA nucleotides to the amino acid sequence of proteins.
RNA is the Missing Link Between ...

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

Genome Size and the Evolution of New Genes

Gene Families

Students who demonstrate understanding can ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. Assessment Boundary: Assessment does not include the phases of meiosis or the biochemical mechanism of specific steps in the process.

3.1.9-12.P

Genomic DNA in Prokaryotes

The genome of most prokaryotic organisms consists of double-stranded DNA organized into one circular chromosome in a region of cytoplasm called the ...

Binary Fission

Fission is the division of a single entity into two or more parts, which regenerate into separate entities that resemble the original. Organisms in the ...

Genomic DNA in Eukaryotes

Eukaryotes have large genomes compared to prokaryotes. To fit their genomes into a cell, eukaryotic DNA is packaged extraordinarily tightly inside the ...

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 is a carefully orchestrated set of cell divisions, the goal of which&#x2014;in humans&#x2014;is to produce haploid sperm or eggs, each containing ...

Meiosis II

Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 ...

Crossing Over

Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where ...

Nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed ...

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 ...

Students who demonstrate understanding can make and defend a claim based on evidence that inheritable genetic variations may result from (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors. Assessment Boundary: Assessment does not include the phases of meiosis or the biochemical mechanism of specific steps in the process.

Gene Evolution Rates and Selection

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