La clonación es la acción de reproducir a un ser de
manera perfecta en el aspecto fisiológico y bioquímico de una célula
originaria, esta definición quiere decir que a partir de una célula de un
individuo se crea otro exactamente igual al anterior, ya que los caracteres que
puede mostrar un ser humano se deben a los genes que ha heredado de los
progenitores. Mediante la clonación se obtiene que el individuo tenga los
mismos genes que el padre o la madre, la reproducción sexual se sustituye por
la reproducción artificial, pero los genes los aporta una única persona, el
individuo tendrá los mismos genes, pero está demostrado científicamente, que es
posible que sus rasgos puedan oscilar.
Hace más de veinte años los científicos estudiaban sobre
la clonación. Los primeros que tuvieron éxito fueron los biólogos americanos
Robert Briggs y Thomas King que clonaron por primera vez una rana en 1952. Unos
años más tarde, en febrero de 1997, un grupo de genetistas anunciaron que
habían clonado una oveja llamada Dolly, que era exactamente igual a su madre.
Esta oveja que nació el cinco de Julio de 1996, se convirtió en el primer
mamífero clonado.
El proceso de la clonación es el mismo con cualquier
animal, para empezar se extrae una célula del que será su madre o padre
biológico, y un óvulo de la madre de alquiler, éste es vaciado de ADN, para que
no posea información genética, y mediante una descarga eléctrica se le fusiona
la célula extraída de la madre, su división crea un embrión el cual al ser
introducido en el útero de la madre de alquiler evolucionará hasta dar lugar a
un hijo casi igual a su padre.
No se puede conseguir una copia exacta respecto al
físico, ya que cada persona tiene grupos de células que se activan en un
determinado momento y que dan lugar a cambios en su imagen. Su personalidad,
afortunadamente tampoco sería idéntica, ya que depende en cierto modo de la
educación y el ambiente en que crezca. Además de esto, al igual que si alguien
tiene una enfermedad hereditaria, mediante la reproducción sexual sólo tiene un
porcentaje de posibilidades de que sus descendientes la hereden, mediante la
clonación tienen el 100% de posibilidades de que la padezcan, ya que mediante
la manipulación genética no se pueden corregir los defectos, pero además
pensando un poco se puede llegar a la conclusión de que al ser tratados los
genes por humanos pueda producirse más fácilmente una mutación.
TYPES OF CLONING
There are different types of cloning by the method:
Partition (fission) of early embryos:
the partition of an embryo, or separation of blastomeres in preimplantation embryos (for 2-32 cells). Each half piece or cut off the embryo is introduced into a zona pellucida another egg, or an artificial cover (ZPA), and implants.
The result is virtually identical to each other individuals (unless somatic mutations), but different from their parents. They would be equivalent to monozygotic twins.
It should not be considered as cloning strictly.
End of the partition:
-In Animals:
Basic research.
Improving fertility of the species used.
Human-in:
To improve outcomes for women with poor ovarian stimulation.
Identical twins separated in time.
Paraclonación: is nuclear transfer from embryonic blastomeres or fetal cells in culture to enucleated unfertilized eggs and sometimes into enucleated zygotes. The "parent" of the clones is the embryo or fetus. These cores are transferred to an enucleated egg or zygote which have been removed pronuclei. This provides mitochondria recipient egg, and in the case of the zygote, sperm something.
The results are almost identical, but different parent individuals of the embryo that provided the transferred nucleus. a generation is lost, because the embryo donor nucleus is destroyed. Individuals born thus seem (from the standpoint of the nuclear genome) the individual which arose the embryo destroyed.
Paraclonación late:
-In Animals:
Research identical individuals.
Livestock production.
Along with cloning, for biotechnology fabrics "humanized" pharming.
Sources tissues for xenotransplantation.
Human-in:
Basic and applied research.
Therapy for mitochondrial diseases that cause blindness or epilepsy nuclear transfer embryo to an egg-zygote recepetor.
Cloning true: the nuclear transfer cells from individuals already born to enucleated eggs or zygotes. Almost identical individuals originate each other (except somatic mutations) and very similar to the donor (which are differentiated somatic mutations in the mitochondrial genome and, proceeding from the recipient egg). The results are almost identical and nearly identical to its parent (donor nucleus) individuals.
The true purpose of cloning:
-In Animals:
Improved knowledge in biomedicine.
Disease models.
With transgenesis: drug production.
Organs for xenotransplantation: transgenic pigs with human complement factor inhibitor.
Livestock-in:
Obtaining transgenic animals. Homologous recombination to generate knockout animals and substituted inactivated genes. Production of therapeutic proteins.
-In The true human cloning may have two different uses:
Reproductive cloning: to create a cloned individual.
No reproductive cloning: cell manipulation is done but the embryo does not implant in the uterus, it can serve different purposes, mainly for research: fertility, embryonic development, procurement of stem cells and induction of differentiation into different tissues.
TECHNIQUES USED IN THE CLONING
The real challenge was to clone a mammal. These are different ways to clone a mammal:
-a Procedure for completely similar to each other, but not the mother, is cloned calves fertilize an egg in a test tube with sperm cow a bull. By the time the division of the fertilized egg has reached a certain stage, the cells that compose it apart, because each of them alone can generate a complete individual. During fetal development (when they appeared the main structures of the body), a specialization of cells, designed to perform various functions will be checked. Before this happens, they implanted one by one the nuclei of cells in fertilized eggs taken from cows and other private core; They are grown in a test tube until they reach the stage of 80-100 cells and implanted in the uterus of surrogate mothers. Animals born clones are equal to each other, because they have the same genetic chain. But this procedure is impossible to obtain calves with identical characteristics of the natural mother, since the union of egg and sperm results in a mixture of genetic heritage.
Dolly, however, is the daughter of a different technique. Indeed, there has been obtained from an embryonic cell, but a somatic cell (in this case, taken from the mammary gland), belonging to an adult and only specializing in performing a particular function animal. The Dolly case demonstrated that it is possible to return to the stage this cell that can lead, in itself, a complete organism. Researchers at the Roslin Institute performed the fusion of fertilized egg cell and no coreless taken from another sheep. The fusion was induced with the aid of a virus. The clone thus obtained was forced to replicate with electric shocks and then was implanted into the uterus of a foster mother. The new being generated is absolutely identical to the sheep that produced the mammary cell. And therefore, it has all its genetic heritage.
A year after the birth of Dolly, the University of Massachusetts and Advanced Cell Technology (a biotechnology company) they achieved a bovine cloning. This is obtained clones fibroblast cells (ie, connective tissue) embryo. It is a compromise between the first generation clones Dolly. Fibroblasts are, in fact, already in differentiated cells but not as part of the adult. Initially six clones implanted in as many adoptive mothers were achieved. Two aborted and the world came only four calves. One of them died five days, but the other continued to grow. Besides being clones, these calves are also (genetically modified) transgenic animals to study the possibility of making drugs for man milk the cow.
-The February 20, 1998, was born in France, Marguerite, a cow clone obtained starting from fetal muscle cells. The novelty lies in the fact that the cells were not taken from an embryo but a fetus (which, regarding the embryo is endowed with all the main structures of the body, although not yet developed). So, it was a stage of cells with very advanced specialization. Marguerite died on March 25, 1998 by an infection of the umbilical cord. But Narcisse survived, a male calf obtained with the same technique.
OBSTÁCULOS EN LA CLONACIÓN
Clonar un mamífero es más complicado si la célula
utilizada se encuentra en un estadio de especialización avanzado. Para obtener
a Dolly, los investigadores ingleses han tenido que clonar 227 células, de las
que sólo 29 estaban en condiciones de poder ser implantadas en el útero de las
madres adoptivas. Sólo en un caso, Dolly, el embarazo llegó a termino.
Esta elevada tasa de fracasos se debe al hecho de que, a
menudo, los clones dan origen a fetos de dimensiones demasiado grandes. Los
riñones y los pulmones no están suficientemente desarrollados y los neonatos
mueren por insuficiencia respiratoria. Es posible que sea también la
manipulación en laboratorio la que provoque alteraciones en los cromosomas y
otros defectos, pero por el momento los científicos no son capaces de ir más allá.
El mismo nacimiento de Dolly presenta muchos puntos
oscuros. Ni siquiera se sabe el tipo de célula de la que la oveja ha sido
clonada. Se trata de una célula de la glándula mamaria, pero no cual
específicamente. Podría ser una célula de la sangre, del sistema inmunitario,
del tejido, etc. Por ello, la técnica utilizada por el Roslin Institute para el
nacimiento de Dolly no es repetible.
Los investigadores de la Universidad de Pavía han
intentado tomar otro camino. Viajaron hasta Honolulú y allí, con la colaboración
de un profesor de la Universidad de Hawwai, llevaron a buen puerto la clonación
de unos cincuenta ratones. Eligieron los ratones porque son los mamíferos más
estudiados en los laboratorios de todo el mundo. De ellos se conocen muchas
cosas, mucho más de lo que sabemos de las ovejas, de las vacas e incluso que de
los seres humanos. Además se ha establecido con certeza el tipo de célula
clonada, información indispensable para poder repetir el experimento. Se trata
de células pertenecientes al tejido del ovario que rodea al óvulo. Otra
diferencia respecto a la clonación de Dolly reside en que el equipo del Roslin
Institute fundió la célula somática con la célula del óvulo sin núcleo,
mientras que en caso de los ratones el núcleo de la célula folicular fue
extraído con un microtubo y transferido a una célula óvulo ( a su vez, sin
núcleo). El primer ratón nacido mediante esta técnica, una hembra, fue a su vez
reclonado y así sucesivamente, hasta conseguir unos cincuenta ejemplares.
Dado que los ratones tienen embarazos mucho mas cortos
que las ovejas (unos diecinueve días frente a varios meses), en muy poco tiempo
se pudo comprobar cómo los ratones de segunda generación pueden procrear con
total normalidad.
ETHICAL ISSUES OF CLONING
The cloning poses serious problems today in society and especially in the world of science.
The bioethical institute, the foundation of Health Sciences, announced the creation in Spain of the expert committee on bioethics and cloning. A group of scientists meeting in Madrid ensures that even in five years, will not be possible to apply safe techniques of cloning and this not for the purpose of replicating human beings, but to cure thousands of genetic diseases, make drugs in transgenic animals, make genoinjertos and have human cells for transplantation.
Scientists and lawyers participating in the seminar "On the frontiers of life science and ethics of cloning", held in Madrid, say human cloning with current technology would be a nonsense, irresponsible unimaginable consequences: children would be born such malformations that society does not know what to do with them.
Professor Harry Griffin, a parent of Dolly the sheep, was even more explicit, in his presentation, "nuclear transfer cloning," said the most terrible, in the event that saw the light of a cloned child would be the Ignoring completely the legacy hidden in their genes. A heritage transmitted from generation to generation that can hide terrible aberrations or genetic diseases: premature aging, cancer, neurological and psychiatric diseases previously unknown. In short a linked series of genetic disorders for which today no remedy science and could place the human species on the brink of extinction. Not to mention cloning for replacement organs.
Scientists attending this conference were categorical in his judgments, and did not hesitate to judge the claims of physicist Richard Seed, irresponsible. In a clear allusion to this "may be the case of an almighty lord capable of creating a person in his image and likeness, you can make a clone of himself because he has money to afford it." But before we get to that point, he will have left behind a trail of irresponsibility and malformed babies.
Therefore, researchers believe that until a few years biotechnology applied to human cloning, will not have reached the appropriate level of development. First, however, science must pass ethical and moral barriers. The experts gathered in Madrid referred to preclinical trials that will require sacrificing hundreds of human embryos for perfecting cloning techniques.
Link: http://html.rincondelvago.com/clonacion-humana-y-animal.html
