Genética
La genética es el campo de la biología que busca comprender la herencia biológica que se transmite de generación en generación. Genética proviene de la palabra γένος (gen) que en griego significa "descendencia".
El estudio de la genética permite comprender qué es lo que exactamente ocurre en el ciclo celular, (replicar nuestras células) y reproducción, (meiosis) de los seres vivos y cómo puede ser que, por ejemplo, entre seres humanos se transmitan características biológicas genotipo (contenido del genoma específico de un individuo en forma de ADN), características físicas fenotipo, de apariencia y hasta de personalidad.
El principal objeto de estudio de la genética son los genes, formados por segmentos de ADN (doble hebra) y ARN (hebra simple), tras la transcripicion de ARN mensajero, ARN ribosómico y ARN de transferencia, los cuales se sintetizan a partir de ADN. El ADN controla la estructura y el funcionamiento de cada célula, con la capacidad de crear copias exactas de sí mismo, tras un proceso llamado replicación,en el cual el ADN se replica.
En 1865 un monje estudioso de la herencia genética llamado Gregor Mendel observó que los organismos heredan caracteres de manera diferenciada. Estas unidades básicas de la herencia son actualmente denominadas genes.
En 1941 Edward Lawrie Tatum y George Wells Beadle demuestran que los genes [ARN-mensajero] codifican proteínas; luego en 1953 James D. Watson y Francis Crick determinan que la estructura del ADN es una doble hélice en direcciones antiparalelas, polimerizadas en dirección 5' a 3', para el año 1977 Fred Sanger, Walter Gilbert, y Allan Maxam secuencian ADN completo del genoma del bacteriófago y en 1990 se funda el Proyecto Genoma Humano.
La ciencia de la genética
Aunque la genética juega un papel muy significativo en la apariencia y el comportamiento de los organismos, es la combinación de la genética [replicación, transcripción, procesamiento (maduración del ARN] con las experiencias del organismo la que determina el resultado final.
Los genes corresponden a regiones del ADN o ARN, dos moléculas compuestas de una cadena de cuatro tipos diferentes de bases nitrogenadas (adenina, timina, citosina yguanina en ADN), en las cuales tras la transcripcion (síntesis de ARN) se cambia la timina por uracilo —la secuencia de estos nucleótidos es la información genética que heredan los organismos. El ADN existe naturalmente en forma bicatenaria, es decir, en dos cadenas en que los nucleótidos de una cadena complementan los de la otra.
La secuencia de nucleótidos de un gen es traducida por las células para producir una cadena de aminoácidos, creando proteínas —el orden de los aminoácidos en una proteína corresponde con el orden de los nucleótidos del gen. Esto recibe el nombre de código genético. Los aminoácidos de una proteína determinan cómo se pliega en una forma tridimensional y responsable del funcionamiento de la proteína. Las proteínas ejecutan casi todas las funciones que las células necesitan para vivir.
El genoma es la totalidad de la información genética que posee un organismo en particular. Por lo general, al hablar de genoma en los seres eucarióticos nos referimos sólo al ADN contenido en el núcleo, organizado en cromosomas. Pero no debemos olvidar que también la mitocondria contiene genes llamado genoma mitocondrial.
Subdivisiones de la genética
La genética se subdivide en varias ramas, como:
- Clásica o mendeliana: Se preocupa del estudio de los cromosomas y los genes y de cómo se heredan de generación en generación.
- Cuantitativa, que analiza el impacto de múltiples genes sobre el fenotipo, muy especialmente cuando estos tienen efectos de pequeña escala.
- Molecular: Estudia el ADN, su composición y la manera en que se duplica. Asi mismo, estudia la función de los genes desde el punto de vista molecular.
- Evolutiva y de poblaciones: Se preocupa del comportamiento de los genes en una población y de cómo esto determina la evolución de los organismos. En la genetica se pueden encontrar muchos rasgos familiares en comun de la familia como el color de ojos, el color de piel y el color del cabello.
Importancia de la genética
El conocimiento genético ha permitido la mejora extensa en productividad de plantas usadas para el alimento como por ejemplo el arroz, trigo, y el maíz. El conocimiento genético también ha sido un componente dominante de la revolución en salud y asistencia médica en este siglo.
Permite alterar diversos segmentos del ADN, adquiriendo genes nuevos y nuevos rasgos genéticos, así como evitar malformaciones en el ADN.
En el área de la salud ha permitido el tratamiento y prevenir la repetición del Síndrome de Down. La bioingeniería ofrece la esperanza de crear antibióticos más eficaces, además de el descubrimiento de una hormona del crecimiento para combatir el enanismo.
Sin duda la genética juega un papel muy importante en la evolución de la especie, y la erradicación de enfermedades genéticas.
Genetics
Genetics (from Ancient Greek γενετικός genetikos, "genitive" and that from γένεσις genesis, "origin"),
a discipline of biology, is the science of genes,heredity, and variation in living organisms.
Genetics deals with the molecular structure and function of genes, gene behavior in context of a cell or organism (e.g. dominance and epigenetics), patterns of inheritance from parent to offspring, and gene distribution, variation and change in populations,such as through Genome-Wide Association Studies. Given that genes are universal to living organisms, genetics can be applied to the study of all living systems, from viruses and bacteria, throughplants and domestic animals, to humans (as in medical genetics).
a discipline of biology, is the science of genes,heredity, and variation in living organisms.
Genetics deals with the molecular structure and function of genes, gene behavior in context of a cell or organism (e.g. dominance and epigenetics), patterns of inheritance from parent to offspring, and gene distribution, variation and change in populations,such as through Genome-Wide Association Studies. Given that genes are universal to living organisms, genetics can be applied to the study of all living systems, from viruses and bacteria, throughplants and domestic animals, to humans (as in medical genetics).
The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the process of inheritance, only began with the work of Gregor Mendel in the mid-19th century.[6] Although he did not know the physical basis for heredity, Mendel observed that organisms inherit traits via discrete units of inheritance, which are now called genes.
Genes correspond to regions within DNA, a molecule composed of a chain of four different types of nucleotides—the sequence of these nucleotides is the genetic information organisms inherit. DNA naturally occurs in a double stranded form, with nucleotides on each strand complementary to each other. Each strand can act as a template for creating a new partner strand. This is the physical method for making copies of genes that can be inherited.
The sequence of nucleotides in a gene is translated by cells to produce a chain of amino acids, creating proteins—the order of amino acids in a protein corresponds to the order of nucleotides in the gene. This relationship between nucleotide sequence and amino acid sequence is known as the genetic code. The amino acids in a protein determine how it folds into a three-dimensional shape; this structure is, in turn, responsible for the protein's function. Proteins carry out almost all the functions needed for cells to live. A change to the DNA in a gene can change a protein's amino acids, changing its shape and function: this can have a dramatic effect in the cell and on the organism as a whole.
Although genetics plays a large role in the appearance and behavior of organisms, it is the combination of genetics with what an organism experiences that determines the ultimate outcome. For example, while genes play a role in determining an organism's size, the nutrition and health it experiences after inception also have a large effect.
History
Although the science of genetics began with the applied and theoretical work of Gregor Mendel in the mid-19th century, other theories of inheritance preceded Mendel. A popular theory during Mendel's time was the concept of blending inheritance: the idea that individuals inherit a smooth blend of traits from their parents. Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes rather than a continuous blend. Blending of traits in the progeny is now explained by the action of multiple genes withquantitative effects. Another theory that had some support at that time was the inheritance of acquired characteristics: the belief that individuals inherit traits strengthened by their parents. This theory (commonly associated with Jean-Baptiste Lamarck) is now known to be wrong—the experiences of individuals do not affect the genes they pass to their children. Other theories included the pangenesis of Charles Darwin (which had both acquired and inherited aspects) and Francis Galton's reformulation of pangenesis as both particulate and inherited.
Mendelian and classical genetics
Modern genetics started with Gregor Johann Mendel, a German-Czech Augustinian monk and scientist who studied the nature of inheritance in plants. In his paper "Versuche über Pflanzenhybriden" ("Experiments on Plant Hybridization"), presented in 1865 to the Naturforschender Verein (Society for Research in Nature) in Brünn, Mendel traced the inheritance patterns of certain traits in pea plants and described them mathematically.[9] Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that heredity was particulate, not acquired, and that the inheritance patterns of many traits could be explained through simple rules and ratios.
The importance of Mendel's work did not gain wide understanding until the 1890s, after his death, when other scientists working on similar problems re-discovered his research. William Bateson, a proponent of Mendel's work, coined the word genetics in 1905. (The adjective genetic, derived from the Greek word genesis—γένεσις, "origin", predates the noun and was first used in a biological sense in 1860.) Bateson popularized the usage of the word genetics to describe the study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London, England, in 1906.
After the rediscovery of Mendel's work, scientists tried to determine which molecules in the cell were responsible for inheritance. In 1911, Thomas Hunt Morgan argued that genes are on chromosomes, based on observations of a sex-linked white eye mutation in fruit flies.[14] In 1913, his student Alfred Sturtevant used the phenomenon of genetic linkage to show that genes are arranged linearly on the chromosome.
Nature versus nurture
Although genes contain all the information an organism uses to function, the environment plays an important role in determining the ultimate phenotype—a phenomenon often referred to as "nature vs. nurture". The phenotype of an organism depends on the interaction of genetics with the environment. One example of this is the case of temperature-sensitive mutations. Often, a single amino acid change within the sequence of a protein does not change its behavior and interactions with other molecules, but it does destabilize the structure. In a high temperatureenvironment, where molecules are moving more quickly and hitting each other, this results in the protein losing its structure and failing to function. In a low temperature environment, however, the protein's structure is stable and it functions normally. This type of mutation is visible in the coat coloration of Siamese cats, where a mutation in an enzyme responsible for pigment production causes it to destabilize and lose function at high temperatures.The protein remains functional in areas of skin that are colder—legs, ears, tail, and face—and so the cat has dark fur at its extremities.
Environment also plays a dramatic role in effects of the human genetic disease phenylketonuria.The mutation that causes phenylketonuria disrupts the ability of the body to break down the amino acid phenylalanine, causing a toxic build-up of an intermediate molecule that, in turn, causes severe symptoms of progressive mental retardation and seizures. If someone with the phenylketonuria mutation follows a strict diet that avoids this amino acid, however, they remain normal and healthy.
A popular method to determine how much role nature and nurture play is to study identical and fraternal twins or siblings of multiple birth.Because identical siblings come from the same zygote they are genetically the same. Fraternal siblings however are as different genetically from one another as normal siblings. By comparing how often the twin of a set has the same disorder between fraternal and identical twins, scientists can see whether there is more of a nature or nurture effect. One famous example of a multiple birth study includes the Genain quadruplets, who were identical quadruplets all diagnosed with schizophrenia.
Medicine
Medical genetics seeks to understand how genetic variation relates to human health and disease. When searching for an unknown gene that may be involved in a disease, researchers commonly use genetic linkage and genetic pedigree charts to find the location on the genome associated with the disease. At the population level, researchers take advantage of Mendelian randomization to look for locations in the genome that are associated with diseases, a method especially useful for multigenic traits not clearly defined by a single gene. Once a candidate gene is found, further research is often done on the corresponding gene (called an orthologous gene) in model organisms. In addition to studying genetic diseases, the increased availability of genotyping methods has led to the field of pharmacogenetics—studying how genotype can affect drug responses.
Individuals differ in their inherited tendency to develop cancer,and cancer is a genetic disease. The process of cancer development in the body is a combination of events.Mutations occasionally occur within cells in the body as they divide. Although these mutations will not be inherited by any offspring, they can affect the behavior of cells, sometimes causing them to grow and divide more frequently. There are biological mechanisms that attempt to stop this process; signals are given to inappropriately dividing cells that should trigger cell death, but sometimes additional mutations occur that cause cells to ignore these messages. An internal process of natural selection occurs within the body and eventually mutations accumulate within cells to promote their own growth, creating a cancerous tumor that grows and invades various tissues of the body.
Normally, a cell divides only in response to signals: "growth factors", it stops growing when making contact with surrounding cells (contact inhibition), and in response to growth inhibitory signals, it divides a limited number of times and dies (apoptosis), it stays inside the epithelium and is not able to migrate to invade other organs. To become a cancer cell, a cell has to accumulate mutations in a number of genes (3-7) that allow it to bypass all these regulations: it no longer needs growth factors to divide, it continues growing when making contact to neighbor cells, and ignores inhibitory signals, it will keep growing indefinitely and is immortal, it will escape from the epithelium and ultimately may be able to escape from the primary tumor, cross the endothelium of a blood vessel, be transported by the bloodstream and will colonize a new organ, forming deadly metastasis. Although there are some genetic predispositions in a small fraction of cancers, the major fraction is due to a set of new genetic mutations that originally appear and accumulate in one or a small number of cells that will divide to form the tumor and are not transmitted to the progeny (somatic mutations). The most frequent mutations are a loss of function of p53 protein, a tumor suppressor, or in the p53 pathway, and gain of function mutations in the ras proteins, or in other oncogenes.
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