Name: when genes cause embryonic death
Uploaded: 2021-04-07T12:11:58.000Z
Duration: 2 min 41 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

Lethal Alleles

Un allèle qui entraîne la mort d’un organisme est appelé allèle létal. Les allèles létaux impliquent toujours des gènes essentiels, qui sont nécessaires à la survie d’un organisme.
Lorsqu’une mutation est causée par un allèle létal dominant, les homozygotes et les hétérozygotes qui héritent de l’allèle périssent.
Les allèles létaux dominants sont rarement identifiés dans les populations car les individus atteints sont souvent éliminés rapidement. Une exception notable à cette observation est la maladie de Huntington, un trouble neurologique qui conduit finalement à la mort.
Cependant, la maladie ne se déclare qu’à l’âge de 40 ans. À ce moment-là, de nombreux individus touchés ont déjà transmis leurs allèles mutants à leur progéniture.
Contrairement aux allèles létaux dominants, les allèles létaux récessifs n’entraînent que la mort des homozygotes.
Un exemple de gène essentiel est agouti, qui est responsable de la détermination de la couleur du pelage chez la souris. Agouti a été étudié pour la première fois en 1905 par Lucien Cuénot et est représenté ici avec un A majuscule pour agouti.
Cuénot a expérimenté sur l’allèle de type sauvage du gène agouti, qui est fonctionnel et donne lieu à une couleur de pelage gris chez la souris. Une telle souris est appelée « agouti » en couleur.
Un allèle mutant du gène agouti n’est pas fonctionnel et donne une couleur de pelage jaune chez la souris.
Cuénot a croisé deux souris jaunes et a observé 2 souris jaunes pour chaque souris grise, dans un rapport de 2:1. Cela a montré que la couleur jaune du pelage est un phénotype dominant. Notamment, ces résultats ne correspondaient pas au rapport phénotypique attendu de Mendel de 3:1 pour un croisement monohybride.
Pour identifier le génotype des souris jaunes, il a effectué un croisement test où des souris jaunes ont été croisées avec des souris grises homozygotes de type sauvage. La moitié de la progéniture résultante était de couleur grise et l’autre moitié était jaune, dans un rapport de 1:1, ce qui indiquait que toutes les souris jaunes étaient hétérozygotes et qu’aucune souris jaune n’était homozygote.
En 1910, W. E. Castle et C. C. Little ont démontré que lorsque deux hétérozygotes étaient croisés, un quart de la progéniture mourait au cours du développement embryonnaire.
Les embryons échoués étaient homozygotes pour l’allèle agouti mutant, ce qui suggère qu’il s’agit d’un allèle létal récessif. Cela explique pourquoi Cuénot n’a jamais observé de souris jaunes homozygotes, et les chiffres ne correspondaient pas à un rapport mendélien typique.

<ol>
	<li>Lobo, I. (2008) Ratios mendéliens et gènes létaux. Éducation à la nature 1(1) :138.</li>
	<li>Michaud, Edward J., Scott J. Bultman, Lisa J. Stubbs et Richard P. Woychik. « La létalité embryonnaire de souris jaunes létales homozygotes (Ay/Ay) est associée à la perturbation d’une nouvelle protéine de liaison à l’ARN. » Genes & development 7, no. 7a (1993) : 1203-1213.</li>
	<li>Miltenberger, Rosalynn J., Randall L. Mynatt, J. Erby Wilkinson et Richard P. Woychik. « Le rôle du gène agouti dans le syndrome de l’obésité jaune. » Le Journal de la nutrition 127, n° 9 (1997) : 1902S-1907S.</li>
	<li>McKusick, Victor A., Thaddeus E. Kelly et John P. Dorst. « Observations suggérant l’allélisme des gènes de l’achondroplasie et de l’hypochondroplasie. » Journal de génétique médicale 10, n° 1 (1973) : 11-16.</li>
</ol>

allèles létaux

Agouti : un allèle létal

Lucien Cuénot a découvert les allèles létaux en 1905 en étudiant l'hérédité de la couleur du pelage chez la souris. Le gène agouti est responsable de la couleur du pelage chez la souris. Ce gène code pour une protéine de signalisation agouti, qui est responsable de la distribution de la mélanine chez les mammifères. L'allèle de type sauvage donne lieu à un pelage gris-brun chez la souris, tandis que l'allèle mutant donne lieu à un pelage jaune. Outre la couleur du pelage, le gène agouti est associé au syndrome d'obésité de la souris jaune, caractérisé par l'apparition précoce de l'obésité et de tumeurs.

Dans une expérience de reproduction, Cuénot a croisé deux souris jaunes et a observé que deux petits étaient jaunes et un gris. La descendance n’a jamais montré le rapport phénotypique de 3 : 1 attendu d’un croisement monohybride. Au lieu de cela, ils ont montré un rapport phénotypique de 2 : 1 entre les souris jaunes et grises.

En 1910, N.E. Château et C.C. Little a démontré que les souris jaunes manquantes mouraient au stade embryonnaire. L'embryon portait les deux allèles mutants récessifs, une condition homozygote qui affecte la différenciation de la masse cellulaire interne (ICM) et du trophectoderme, la couche externe du blastocyste.

Allèles létales chez les humains

Certains allèles mortels récessifs provoquent des troubles génétiques chez l’homme. Par exemple, l’achondroplasie est une maladie génétique qui affecte le développement osseux, entraînant un nanisme des membres courts. Elle est causée par un allèle dominant, ce qui signifie que la présence d’une seule copie de l’allèle muté est à l’origine du trouble. Cependant, lorsque le même allèle est présent sous forme homozygote, il devient mortel et provoque la mort au cours du développement embryonnaire. Même si la maladie est causée par un allèle dominant, la létalité est récessive ; par conséquent, on l’appelle un allèle mortel récessif.

De même, les allèles létales dominants peuvent également provoquer des troubles génétiques chez l’homme. De tels allèles létales provoquent la mort même s'ils sont présents en un seul exemplaire. La plupart du temps, ces allèles sont difficiles à trouver dans une population car ils provoquent la mort précoce d’un organisme. Un exemple d’allèle létal dominant est la maladie de Huntington, un trouble neurologique mortel. L’apparition de cette maladie est lente, ce qui permet aux hétérozygotes de survivre après la naissance. Si la personne survit jusqu’à l’âge de procréer, les gènes sont transmis à sa progéniture. De cette façon, l’allèle persiste dans la population.

Allèles létaux

Agouti : un allèle mortel
Lucien Cuénot a découvert les allèles létaux en 1905 alors qu’il étudiait l’hérédité de la couleur du pelage chez la souris. Le gène agouti est ...

Education

Enseignement

JoVE Core

Molecular Biology

Biologie moléculaire

Unit 2

Unité 2

Mendelian Genetics

La génétique mendélienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 crossed two yellow mice, he expected the 3:1 ratio seen in a monohybrid cross, but the offspring showed a 2:1 ratio of yellow to gray mice instead.

W.E. Castle and C.C. Little later explained the missing yellow offspring in 1910. The homozygous mutant embryos were dying during embryonic development. This lethal combination affected the differentiation of both the inner cell mass, or ICM, and the trophectoderm, the outer layer of the blastocyst.

Lethal alleles can also affect humans. Achondroplasia is a genetic disorder that causes short-limbed dwarfism and affects bone development. It is caused by a dominant allele, but the same allele is recessive lethal in homozygous form, because two copies lead to death during embryonic development.

Some dominant lethal alleles can also persist in populations. Huntington’s disease is an example of a dominant lethal allele that causes a fatal neurological disorder. Because its onset is slow, people with one copy can survive after birth and may reach reproductive age, which allows the allele to be passed to offspring.

When Genes Cause Embryonic Death

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

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

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

Explore how lethal alleles alter inheritance in mice and humans, from the agouti gene and embryonic death to achondroplasia and Huntington’s disease.

When Genes Cause Embryonic Death | JoVE K12

molecular biology

JoVE Core Biologie Moléculaire illustre les processus moléculaires au sein de la cellule grâce à des leçons vidéos claires et concises. Les applications de ces concepts sont ensuite démontrées grâce à des expériences concrètes en laboratoire.

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

Genetic mechanisms and inheritance

Virginia  Standards of Learning

HIgh School

BIO.5

BIO.5.c

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

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 ...

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.

Understand genetic mechanisms for variation.

When Genes Cause Embryonic Death

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