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Reproduccion asexual por regeneracion


Se trata de un cnidario que habita en aguas dulces. El desarrollo no termina con Reproduccion asexual por regeneracion nacimiento de la criatura. Abarca todo el ciclo vital. La hidra parece, vista desde "Reproduccion asexual por regeneracion" perspectiva, inmortal. Los organismos en desarrollo, a diferencia de la diosa, son ensayo, error y riesgo.

Las instrucciones contenidas en el genoma no determinan de forma lineal y sin interferencias el fenotipo. El Profesor Newman ha tenido la amabilidad de respondernos unas preguntas. It has been said that organisms develop from a plan established in the genes. For you, what are genes, in relation to the organism to which they give shape and function? Genes, which are composed of DNA, directly specify the sequences of RNA molecules and indirectly, the amino acid sequences of proteins.

Before there were multicellular forms, single-celled organisms evolved for as much as two billion years driven, in part, by genetic change, as well as by establishment of persistent symbiotic relationships among simpler cells. The protein and RNA molecules produced by cells associate with each other in a context-dependent fashion or, in many cases, catalyze chemical reactions generating lipids, polysaccharides and other moleculeswhose rates depend on the temperature and composition of the external environment.

So the population of molecules inside the cell can vary extensively even if the genes do not. But we now know that this is not always true Reproduccion asexual por regeneracion the rate at which a protein is synthesized, which depends on factors internal and external to the cell, affects the order in which its different portions fold.

So even with the same sequence a given protein can have different shapes and functions. Furthermore, many proteins have no intrinsic shape, taking on different roles in different molecular contexts.

So even though genes specify protein sequences they have only a tenuous influence over their functions. The deployment of information in the genes, moreover, is Reproduccion asexual por regeneracion dependent on the presence of certain RNA and protein molecules in the cell. So, to reiterate, the genes do not uniquely determine what is in the cell, but what is in the cell determines how the genes get used.

Only if the pie were to rise up, take hold of the recipe book and rewrite the instructions for its own production, would this popular analogy for the role of genes be pertinent. When it comes to multicellular organisms, which first arose from single-celled ancestors Reproduccion asexual por regeneracion million years ago, things are even more complicated relative to genetic determination.

Certain unicellular proteins and other molecules mobilize physical effects in the multicellular context that were unanticipated during their earlier evolution. To take a simple example, all single-celled organisms can secrete protein molecules into the environment around them. These molecules will generally float away, but they may serve to attract prey, repel predators, and so forth. The gene involved simply specifies the sequence of the secreted protein.

What function the protein comes to assume in the new multicellular context has nothing to do with the evolutionary history of that gene, or the selection to which it had been subject.

There are many other such examples. The development of developmental biology leads us to consider the evolution of species in a different light. How are the process of species evolution and the development of organisms mutually affected? Does development explain, rather than Darwinian natural selection, speciation?

What we have been learning about development is that the mechanisms it employs for the production of form can be both nonlinear and conditional. For most present-day organisms, however, redundant developmental pathways conspire Reproduccion asexual por regeneracion stabilize the generation of a standard phenotypic outcome.

But while the organisms of our experience do not often undergo major morphological reorganization, the circuitry that stabilizes development is itself a product of evolution. What are the major milestones of development? What basic steps are taken on the path leading from the zygote to the body? Confining the question to animal development, my own specialty, we find that the formation of a cluster of relatively similar-sized cells, variously called a blastula, pregastrula, or inner cell mass, is common to all phyla.

This can occur, as in mammals, by division of Reproduccion asexual por regeneracion small zygote i. The cells are generally held together by one or more members of the cadherin family of cell surface proteins.

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