Name: forked line method for trihybrid crosses
Uploaded: 2021-04-07T12:11:58.000Z
Duration: 2 min 27 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.7.1

Trihybrid Crosses

מנדל הרחיב את מחקרו על צמחי אפונה לצלבים תלת-היברידיים, שבהם האורגניזמים נבדלים זה מזה בשלוש תכונות שונות, למשל, גובה הצמח - המסומן כאן באותיות גדולות או קטנות T, צורת הזרע המוצגת כאן על ידי האלל R, וצבע הזרעים - המסומן באות Y. 
צמח הומוזיגוטי דומיננטי בצלב זה יהיה צמח גבוה עם זרעים עגולים וצהובים והגנוטיפ TTRRYY באותיות גדולות. צמח הומוזיגוטי רצסיבי יהיה צמח קצר עם זרעים מקומטים וירוקים וגנוטיפ באותיות קטנות.
כאשר צמחים אלה מוצלבים, כל הצמחים מדור F1 הם תלת-היברידיים, כלומר הם הטרוזיגוטיים עבור כל שלוש התכונות עם הגנוטיפ המוצג כאן.
צמחי דור F1 מציגים את הפנוטיפ הדומיננטי שבו כל הצמחים גבוהים... עם זרעים עגולים..., צהובים.
כאשר ישנם שלושה זוגות של מאפיינים מנוגדים, ריבוע פונט הופך במהירות ללא מעשי מכיוון שיש 64 גנוטיפים פוטנציאליים בדור F2.
במקרים כאלה, שיטת הקו המפוצל משמשת לעתים קרובות במקום. כאן, הטרוזיגוטים F1 עם שלושה זוגות של תכונות מסודרים בשלוש שורות, כאשר כל גן תופס שורה אחת.
האללים לגובה הצמח ממוקמים בשורה הראשונה ומופרדים ביחס המצופה מהצלבים החד-היברידיים, שבהם שלושה צמחים גבוהים וצמח אחד נמוך.
האללים לצורת הזרע ממוקמים בשורה השנייה ומופרדים על קו מפוצל באופן דומה, ביחס של 3 ל-1. התהליך חוזר על עצמו שוב בשורה השלישית עם האללים לצבע הזרע.
כעת הערכים לאורך כל נתיב מפוצל מוכפלים עבור כל אחת משמונה התוצאות השונות.
לדוגמה, בעקבות המזלג הרחוק ביותר משמאל, שלוש פעמים שלוש כפול שלוש הוא 27. לכן, בין 64 הגנוטיפים הפוטנציאליים לדור זה, ישנם 27 צמחים גבוהים עם זרעים עגולים וצהובים. 
לאחר מכן ניתן להכפיל כל נתיב כדי למצוא את היחסים הפנוטיפיים עבור כל דור F2.

<ol>
	<li>סנוסטאד, ד. פיטר ומייקל ג'יי סימונס. עקרונות הגנטיקה. ג'ון ויילי ובניו, 2015. עמודים 46 - 47.</li>
	<li>"דיני ירושה", כניסה לאתר ב-10 במאי 2021 <a href="https://www.oercommons.org/courseware/module/14996/student/?task=5">https://www.oercommons.org/courseware/module/14996/student/?task=5</a></li>
</ol>

צלבים טריהיברידיים

<div style="direction: rtl;">
חלק מהצלבים של מנדל בחנו שלושה זוגות של מאפיינים מנוגדים. צלב כזה נקרא צלב תלת-היברידי. הצלבה תלת-היברידית היא שילוב של שלושה צלבים מונו-היברידיים בודדים. לדוגמה, גובה הצמח (גבוה לעומת נמוך), צורת זרע (עגול לעומת מקומט) וצבע הזרע (צהוב לעומת ירוק).

הצמחים מדור F1 של צלב תלת-היברידי הם הטרוזיגוטיים לכל שלוש התכונות ומייצרים שמונה גמטות. עם הפריה עצמית, לגמטות אלו יש סיכוי שווה להוליד 64 שילובים שונים של גנוטיפים בדור F2. במקרים כאלה, כשיש יותר משני זוגות של מאפיינים מנוגדים שצריך לחקור, ריבוע של פאנט הוא מסורבל ולא מעשי. ניתן להשתמש בשיטת קו המזלג במקום ריבוע פאנט כדי לפשט את חיזוי יחסי הגנוטיפ והפנוטיפ.

למרות שאי אפשר לחזות את המספר האמיתי של פרטים לכל גנוטיפ בדור F2, שיטה זו יכולה לחזות את היחס הפנוטיפי, 27:9:9:9:3:3:3:1. בהצלבה הכוללת צמחים גבוהים עם זרע עגול צהוב וצמחים ננסיים עם זרעים מקומטים וירוקים, ניתן לצפות למצוא 27 צמחים גבוהים עם זרעים עגולים וצהובים, 9 צמחים קצרים עם זרעים צהובים, עגולים, 9 צמחים גבוהים עם צהוב ומקומט. זרעים, 9 צמחים גבוהים עם זרעים ירוקים, עגולים, 3 צמחים קצרים עם זרעים צהובים ומקומטים, 3 צמחים קצרים עם זרעים ירוקים, עגולים, 3 צמחים גבוהים עם זרעים ירוקים ומקומטים, וצמח אחד קצר עם זרעים ירוקים ומקומטים.

כללים של הפריה רב היברידית

ישנם כללים לזיהוי הגמטות והגנוטיפים של הצאצאים של דורות F1 ו-F2, בהתאמה. כללים אלו חלים על כל הצלבים הרב-היברידיים המצייתים לחוק ההתפלגות העצמאית ועוקבים אחר הדפוס הדומיננטי-רצסיבי. ניתן לזהות את מספר הגמטות שנוצרו ביצירת F1 באמצעות נוסחת 2n, כאשר n הוא מספר זוגות הגנים ההטרוזיגוטים. לדוגמה, רבייה בין XxYy ו-XxYy הטרוזיגוטים יש n של 2. לפיכך, מספר הגמטות שנוצרו על ידי ההטרוזיגוטים F1 יהיה 22, שהם ארבע.

באופן דומה, לגידול בין הטרוזיגוטים XXYy ו-XXyY יש n של 1 מכיוון ש-X אינו הטרוזיגוטי. מכאן שמספר הגמטות שנוצרו על ידי ההטרוזיגוטים F1 יהיה 21, שהם 2. באופן דומה, ניתן לזהות את הגנוטיפ של דור F2 באמצעות נוסחת 3n.
</div>

צלבים תלת-היברידיים
חלק מהצלבים של מנדל בחנו שלושה זוגות של מאפיינים מנוגדים. צלב כזה נקרא צלב תלת-היברידי. A ...

Education

JoVE Core

Molecular Biology

ביולוגיה מולקולרית

Unit 2

יחידה 2

Mendelian Genetics

גנטיקה מנדלית

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

forked line method for trihybrid crosses

Forked line method for trihybrid crosses helps predict the outcome of three-trait Mendelian crosses. A trihybrid cross studies three pairs of contrasting characteristics. It combines three separate monohybrid crosses. Common examples include plant height, seed shape, and seed color.

In a typical trihybrid cross, the F1 plants are heterozygous for all three traits. They can produce eight different gametes. After self-fertilization, these gametes can lead to 64 genotype combinations in the F2 generation. When more than two contrasting traits are studied, a Punnett square becomes hard to use. The forked line method gives a simpler way to predict genotype and phenotype ratios.

This method does not predict the exact number of offspring in the F2 generation. It can predict the phenotypic ratio instead. For a cross between tall plants with round, yellow seeds and dwarf plants with wrinkled, green seeds, the expected ratio is 27:9:9:9:3:3:3:1. That means 27 tall plants with round, yellow seeds, 9 short plants with yellow, round seeds, 9 tall plants with yellow, wrinkled seeds, 9 tall plants with green, round seeds, 3 short plants with yellow, wrinkled seeds, 3 short plants with green, round seeds, 3 tall plants with green, wrinkled seeds, and 1 short plant with green, wrinkled seeds.

Rules for multi hybrid fertilization also help identify gametes and F2 genotypes. These rules apply to crosses that follow independent assortment and a dominant-recessive pattern. The number of gametes in the F1 generation can be found with the 2n formula, where n is the number of heterozygous gene pairs. For example, XxYy × XxYy gives four gametes because n equals 2. If one gene is not heterozygous, as in XXYy × XXyY, n equals 1 and the F1 plants form two gametes. The genotype of the F2 generation can then be found with the 3n formula.

Forked Line Method for Trihybrid Crosses

punnett squares

Predicting Traits with Punnett Squares

Punnett squares help students predict how traits may be passed from parents to offspring. They are a simple grid used in genetics to organize possible allele combinations. An allele is a version of a gene. The square compares the alleles each parent can give. By filling in the boxes, students can see possible genotypes, which are the genetic makeup of offspring. The results can also help connect those genotypes to traits that may appear in the next generation.

monohybrid crosses

Tracking One Trait in Monohybrid Crosses

Monohybrid crosses track how one trait is passed from parents to offspring. They are used to study inheritance when only a single characteristic is followed at a time. A monohybrid cross can compare the possible outcomes for a monogenic trait, which is a trait controlled by one gene. This approach helps show how one gene can shape different inherited forms of the same characteristic. The method also connects with Mendel's work on genetics. It is a useful way to predict patterns of inheritance...

dihybrid crosses

Predicting Two-Trait Genetic Crosses

Dihybrid crosses are used to predict how two traits can be passed from parents to offspring. A dihybrid cross tracks two genes at the same time, so it helps students see how different alleles can combine in a genetic pattern. This topic is closely tied to Mendelian genetics and independent assortment. Independent assortment means that allele pairs for different traits can separate into gametes independently of one another. When students work through a dihybrid cross, they can compare the...

trihybrid crosses

Forked line method for trihybrid crosses helps predict the outcome of three-trait Mendelian crosses. A trihybrid cross studies three pairs of contrasting characteristics. It combines three separate monohybrid crosses. Common examples include plant height, seed shape, and seed color. In a typical trihybrid cross, the F1 plants are heterozygous for all three traits. They can produce eight different gametes. After self-fertilization, these gametes can lead to 64 genotype combinations in the F2...

law of independent assortment

Independent Chromosome Assortment in Meiosis

Independent chromosome assortment in meiosis explains how different gene pairs can be inherited independently. This idea is one of Mendel’s laws of inheritance and is often called the law of independent assortment. The pattern depends on how homologous chromosomes line up during meiosis I. Each chromosome pair orients independently of the others, so the maternal and paternal chromosomes can separate into different gametes in many combinations. This random separation helps create genetic...

chi-square analysis

Chi-Square Test in Genetics

The chi-square test in genetics helps compare expected and observed results. It is a statistical hypothesis test used to see whether a difference between an expected value and an observed value is significant. In genetics, it helps decide whether to accept or reject a hypothesis based on how far the observed data moves from the expected data. The test was developed by Pearson in 1990. The first step is to set up a null hypothesis. This hypothesis says there is no real difference between the...

pedigree analysis

Tracing Traits with Pedigree Charts

Pedigree analysis uses family trees, called pedigrees, to trace how traits and diseases pass from one generation to the next. A pedigree chart helps scientists and students see inheritance patterns clearly across relatives. The chart uses standard symbols to show family members and their relationships. It can reveal whether a trait is likely passed through dominant or recessive inheritance, and it can also help identify patterns linked to sex chromosomes. By studying a pedigree, it is...

multiple allele traits

Multiple Alleles in Trait Inheritance

Multiple alleles can shape how a trait is inherited in a population. A gene may have more than two allele forms, even though each person still carries only two alleles for that gene. These allele combinations can produce traits with more than two possible outcomes. The ABO blood group system is a common example of a multiple allele trait. It shows how different alleles can interact to determine an organism’s phenotype, or observable trait. Multiple allele traits help explain why inheritance...

incomplete dominance

Incomplete Dominance in Traits and Disease

Incomplete dominance is a pattern of inheritance where two alleles both affect a trait in a heterozygous organism. In this case, one allele is not fully dominant over the other. The result is a phenotype that looks like a blend or intermediate form. Gregor Mendel’s pea plant experiments helped explain the usual dominant and recessive pattern. He showed that each gene in a diploid cell has two alleles, one inherited from each parent. In his model, a dominant allele shows its effect with one or...

lethal alleles

When Genes Cause Embryonic Death

Lethal alleles can change inheritance patterns by causing death before birth. In mice, Lucien Cuénot studied the agouti gene, which helps control coat color through an agouti-signaling protein that affects melanin distribution in mammals. The wild-type allele produces a gray-brown coat, while the mutant allele produces a yellow coat. Cuénot also found that the yellow allele was linked to yellow mouse obesity syndrome. This syndrome is associated with early-onset obesity and tumors. When he...

polygenic traits

Traits Shaped by Many Genes

Polygenic traits are characteristics shaped by many genes acting together. This pattern is different from a single-gene trait, where one gene has a larger effect on the outcome. In polygenic inheritance, each gene adds a small contribution to the final trait. Height is a common example of a polygenic trait. Many genes influence human height, so the result can vary across a wide range. These small genetic effects combine to produce differences that are easy to see in a population. Polygenic...

background and environment affect phenotype

background-and-environment-affect-phenotype

How Genes and Environment Shape Traits

Genes and the environment work together to shape phenotype, or the visible traits of an organism. A phenotype can change because of genetic background, environmental conditions, or both. Factors such as temperature, oxygen availability, and mutagens can all influence how a trait appears. Horses show how one gene can affect coat color and how a modifier gene can change that result. The Extension gene controls pigment production in the coat. The wild-type genotype EE produces black pigment,...

x and y chromosomes

Sex Chromosomes in Human Inheritance

Sex chromosomes help determine biological sex in mammals, including humans. Humans have two sex chromosomes, X and Y. Each diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A female usually has two X chromosomes, while a male usually has one X chromosome and one Y chromosome. Egg and sperm cells carry only half the usual number of chromosomes. They contain 22 autosomes and one sex chromosome. Every egg has an X chromosome. Sperm cells can carry either an X or a Y...

the y chromosome determines maleness

Y Chromosome Structure and Male Traits

The Y chromosome is a sex chromosome that helps guide male development in humans and other vertebrates and mammals. Human males usually have one X chromosome and one Y chromosome, along with 22 pairs of autosomes. In these organisms, the presence or absence of the Y chromosome influences whether male traits develop. The Y chromosome evolved from an autosome about 300 million years ago, when two sex chromosomes began to diverge. Since then, it has lost most of its genes and become much smaller.

the ratio of x chromosome to autosomes

Drosophila Sex Determination by X:A Balance

In Drosophila, sex is determined by the balance between X chromosomes and autosomes, not by the X and Y chromosomes alone. The Y chromosome is active in these flies, but it does not set sex. Instead, it carries genes needed for sperm production in adult males. A normal male Drosophila has one X chromosome and two sets of autosomes. A normal female has two X chromosomes and two sets of autosomes. When this X:A ratio changes, flies can develop different sexual phenotypes, including metamales,...

x-linked traits

X-Linked Inheritance in Families

X-linked inheritance in families explains how traits linked to the X chromosome pass from parents to children. These traits are often tracked through family trees because the pattern can differ between males and females. A male has one X chromosome and one Y chromosome. A female has two X chromosomes. Because of this difference, a trait on the X chromosome can show up in a different way depending on the sex of the child. Family examples often include traits such as color blindness. Studying...

sex linked disorders

Sex-Linked Disorders and Inheritance Patterns

Sex-linked disorders are genetic conditions that follow inheritance patterns tied to the sex chromosomes. These disorders help explain how certain traits can appear more often in one sex than the other. The transcript focuses on examples of sex-linked disorders, including Y-linked infertility, Fragile X syndrome, and Duchenne muscular dystrophy. Y-linked infertility is passed through the Y chromosome, while Fragile X syndrome and Duchenne muscular dystrophy are associated with sex-linked...

dosage compensation

X-Chromosome Balance in Animals

X-chromosome balance in animals helps equalize gene expression between males and females. Sex can be determined by the number and type of sex chromosomes. In humans, females have two X chromosomes and males have one X and one Y chromosome. In C. elegans, one X chromosome is male, while two X chromosomes make a hermaphrodite. The X chromosome carries more than sex-related genes. It also includes genes involved in body functions such as brain development and the immune system. Because males and...

x-inactivation

X-Inactivation and Barr Bodies

X-inactivation is a process that reduces gene activity on one X chromosome. It helps balance gene expression in cells that have more than one X chromosome. A key result of this process is the formation of a Barr body, which is the inactive X chromosome seen in the nucleus. This topic also includes Xist, a gene linked to X-inactivation. Xist produces RNA that coats the X chromosome and helps turn it off. Together, Xist and the Barr body show how cells control X-linked genes during development...

blood types

Blood Types and Transfusion Matching

Human blood types help determine safe blood transfusion matching. Blood is classified by antigens on the surface of red blood cells and antibodies in the plasma. Correct blood typing matters because an unsafe match can affect transfusion success. The International Society of Blood Transfusion has identified 38 human blood types, and ABO, Rh, and MNS are among the most common. The ABO blood group depends on antigens made by genes on chromosome 9. Red blood cells carry a base glycoprotein called...

blood transfusion and agglutination

Matching Blood Types for Safe Transfusion

Blood transfusion is a medical treatment used to restore blood volume after major blood loss from an accident or a medical procedure. It works by taking blood from a suitable donor and giving it to a recipient. Safe transfusion depends on matching blood types and checking for immune compatibility. The history of blood transfusion began in the 17th century, when early experiments were done in animals. In 1818, James Blundell, a British doctor, performed the first successful human blood...

key terms and concepts

Learn how the forked line method simplifies trihybrid crosses, predicts the 27:9:9:9:3:3:3:1 ratio, and uses 2n and 3n rules for gametes and genotypes.

Forked Line Method for Trihybrid Crosses | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

Louisiana Student Standards for Science

High School

Life Sciences

Heredity: Inheritance And Variation Of Traits

HS-LS3-1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Heredity

Structure and function of DNA in cells

Genetic mechanisms and inheritance

Alabama Course of Study Science

Heredity: Inheritance and Variation of Traits

9-12.B.3.11.a

Next Generation Science Standards

Life Science

Florida Department of Education

SC.912.L.16

SC.912.L.16.2

Texas Essential Knowledge and Skills

BIO.8

BIO.8.B

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

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

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

Genome Size and the Evolution of New Genes

types-of-genetic-transfer-between-organisms

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.

LS.Bio.6.2

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
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

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.

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

Understand genetic mechanisms for variation.

Forked Line Method for Trihybrid Crosses

Description

Transcript

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