Name: x-inactivation and barr bodies
Uploaded: 2021-04-07T12:11:58.000Z
Duration: 1 min 58 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance And Variation Of Traits

HS-LS3-2

X-inactivation

- [Instructor] En organismos
que poseen múltiples copias

del mismo cromosoma,

como las mujeres que
tienen dos cromosomas X,

debe producirse un proceso
de compensación genética

durante el desarrollo temprano.

La inactivación del cromosoma X, o XCI,

es el proceso en el que uno de
los cromosomas en una célula

es silenciado aleatoriamente
para evitar la sobreexpresión

de los mismos genes.

El cromosoma inactivado se concentra

en una estructura
compacta, el cuerpo Barr,

que es inaccesible para la transcripción.

Cerca del centro de cada cromosoma X

hay una región llamada
Centro de Inactivación X,

que contiene dos
secuencias complementarias

para el ARN no codificante,
llamadas XIST y TSIX,

junto con otras secuencias reguladoras.

XCI es iniciado por activadores

que promueven la transcripción
XIST en el cromosoma

que se desactivará.

Las moléculas de ARN resultantes
recubren el cromosoma XIST,

a partir del cual se producen.

A este paso le sigue un
conjunto de eventos complejos

que incluye el reclutamiento
de copartícipes proteicos,

la reestructuración del ADN

y la producción del cuerpo de Barr.

TSIX se transcribe en una
dirección antisentido a XIST

desde el cromosoma activo,

y actúa para reprimir la actividad XIST

mediante la unión complementaria.

El cromosoma inactivado
en forma de cuerpo de Barr

es muy estable durante
la vida del organismo

y se transmite durante cada
división celular mitótica.

Por ejemplo, las gatas calicó

obtienen su patrón de
múltiples colores en el pelaje

debido al hecho de que

uno de los genes que
codifica el color del mismo

está ligado a X y silenciado
aleatoriamente en las células

en diferentes regiones de su cuerpo.

Ahn, J. y J. X. Lee. "Cromosoma X: inactivación del cromosoma X". Nature Education 1, no. 1 (2008): 24. [<a href="https://www.nature.com/scitable/topicpage/x-chromosome-x-inactivation-323">Fuente</a>]

Disteche, Christine M. y Joel B. Berletch. "Inactivación y escape del cromosoma X". Journal of Genetics 94, no. 4 (diciembre de 2015): 591–99. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4826282/"> </a>[<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4826282/">Fuente</a>]

inactivación del x

El cromosoma X humano contiene más de diez veces más genes que el cromosoma Y. Dado que los machos tienen sólo un cromosoma X y las hembras dos, se podría esperar que las hembras produjeran el doble de proteínas, con resultados indeseables. En cambio, para evitar este posible problema, las células femeninas de los mamíferos inactivan casi todos los genes en uno de sus cromosomas X durante el desarrollo embrionario temprano. En la envoltura nuclear que rodea el núcleo celular, el cromosoma X inactivado se condensa en una bola pequeña y densa llamada cuerpo de Barr. En este estado, la mayoría de los genes ligados al cromosoma X no son accesibles a la transcripción. En los mamíferos placentarios, el cromosoma X inactivado (¿materno o paterno?) se determina al azar (los marsupiales, sin embargo, inactivan preferentemente el cromosoma X paterno). La inactivación de X en una célula también es independiente de la inactivación de X en otras células. Así, aproximadamente la mitad de las células embrionarias inactivan la copia X materna; la mitad restante inactiva la copia paterna, produciendo un mosaico. Cuando estas células se replican, producen células con el mismo cromosoma X inactivado. En particular, los cuerpos de Barr se reactivan en las células dentro de los ovarios que se convierten en óvulos. La inactivación de X explica la aparición de hembras de gato carey y calicó. Estos gatos son heterocigotos para un gen con alelos de pelaje negro y pelaje naranja ubicado en el cromosoma X. Sus pelajes moteados son el resultado de la inactivación aleatoria de los alelos del pelaje negro y naranja en grupos de células (los gatos calicó también tienen manchas de pelaje blanco causadas por un cromosoma diferente). Si bien existen gatos machos de carey y calicó, tienen un cromosoma X adicional y generalmente son infértiles. La inactivación de X reduce la gravedad de las afecciones causadas por cromosomas X adicionales. Los hombres con síndrome de Klinefelter forman cuerpos de Barr para inactivar su cromosoma X adicional. Las mujeres con síndrome Triple X forman cuerpos de Barr adicionales por su exceso de cromosoma o cromosomas X.

Inactivación del X

El cromosoma X humano contiene más de diez veces el número de genes que en el cromosoma Y. Dado que los hombres tienen solo un cromosoma X y las mujeres tienen dos, ...

Education

Educación

JoVE Core

Molecular Biology

Biología Molecular

Unit 2

Unidad 2

Mendelian Genetics

Genética mendeliana

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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 and cell function.

X-Inactivation and Barr Bodies

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

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 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 X-inactivation reduces gene activity on one X chromosome and leads to Barr body formation, with Xist helping silence the chromosome.

X-Inactivation and Barr Bodies | JoVE K12

molecular biology

JoVE Core Biología Molecular presenta los procesos moleculares de la célula a través de lecciones claras y concisas de animaciones audiovisuales. Además, en los vídeos de científicos en acción, se muestran aplicaciones de estos conceptos mediante experimentos reales en laboratorios especializados.

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Biology

Heredity

Genetic mechanisms and inheritance

Alabama Course of Study Science

Heredity: Inheritance and Variation of Traits

9-12.B.3.11.a

Texas Essential Knowledge and Skills

BIO.8

BIO.8.B

myJoVE Corporation

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HS-LS3-1

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HS-LS3-3

X-Inactivation and Barr Bodies

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