explain the molecular theory of recombination with diagram
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In molecular biology, recombination generally refers to the molecular process by which genetic variation found associated at two different places in a continuous piece of DNA becomes disassociated.
Simply, Recombination is the production of new DNA molecule(s) from two parental DNA molecules or different segments of the same DNA molecule. The genetic recombination causes re-arrangement of genes producing altogether new genotypes and phenotypes. These cause variations which lead to evolution.
In this process one or both of the genetic variants are replaced by different variants found at the same two places in a second DNA molecule.
One mechanism leading to such molecular recombination is chromosomal crossing over.
At least four types of naturally occurring recombination have been identified in living organisms.
They are:-
1) General or homologous recombination
2)Illegitimate or non homologous recombination
3) Site specific recombination
4)Replicative recombination.
Simply, Recombination is the production of new DNA molecule(s) from two parental DNA molecules or different segments of the same DNA molecule. The genetic recombination causes re-arrangement of genes producing altogether new genotypes and phenotypes. These cause variations which lead to evolution.
In this process one or both of the genetic variants are replaced by different variants found at the same two places in a second DNA molecule.
One mechanism leading to such molecular recombination is chromosomal crossing over.
At least four types of naturally occurring recombination have been identified in living organisms.
They are:-
1) General or homologous recombination
2)Illegitimate or non homologous recombination
3) Site specific recombination
4)Replicative recombination.
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Hi friend,
In molecular theory the symmetry of the intermediate that is so apparent in the electron micrograph and in the rotated 'open' intermediate (G) in the diagramis the second essential feature that makes the recombination intermediate such a powerful centerpiece of Holliday’s proposed mechanism for genetic recombination. That is, Holliday's proposed recombination intermediate could be broken apart, or matured by cleavage of the two recombining DNA double helixes via two symmetrical alternatives: the cleavage could be from left to right in the diagram to yield the left products in 'H' or from top to bottom to yield the right daughter product in 'H'. In one case the external allelic markers (originally A and B on one input DNA molecule and a, b in the other) retain their parental configuration (H left). In the alternative maturation step, the markers are recombined (H right). Thus, after a recombination event, genetically revealed by the formation of heteroduplex DNA, there is an equal chance that the flanking parental alleles will be either recombined or left in their original parental linkage. This too was known from the study of Neurospora. Thus the formation and maturation of the Holliday intermediate succeeded in satisfying and explaining all of the genetic observations.
The simplicity of the Holliday recombination intermediate and the model that utilizes it was attractive but it was not the only recombination model discussed in the 1960s and early 70s, and there was no genetic way to prove which model was correct. That proof required the use of different techniques and led to our discovery of structures such as the one shown in the electron micrograph, in which DNA molecules were captured in the process of genetic recombination, using the Holliday intermediate.
Hope this helps you....
In molecular theory the symmetry of the intermediate that is so apparent in the electron micrograph and in the rotated 'open' intermediate (G) in the diagramis the second essential feature that makes the recombination intermediate such a powerful centerpiece of Holliday’s proposed mechanism for genetic recombination. That is, Holliday's proposed recombination intermediate could be broken apart, or matured by cleavage of the two recombining DNA double helixes via two symmetrical alternatives: the cleavage could be from left to right in the diagram to yield the left products in 'H' or from top to bottom to yield the right daughter product in 'H'. In one case the external allelic markers (originally A and B on one input DNA molecule and a, b in the other) retain their parental configuration (H left). In the alternative maturation step, the markers are recombined (H right). Thus, after a recombination event, genetically revealed by the formation of heteroduplex DNA, there is an equal chance that the flanking parental alleles will be either recombined or left in their original parental linkage. This too was known from the study of Neurospora. Thus the formation and maturation of the Holliday intermediate succeeded in satisfying and explaining all of the genetic observations.
The simplicity of the Holliday recombination intermediate and the model that utilizes it was attractive but it was not the only recombination model discussed in the 1960s and early 70s, and there was no genetic way to prove which model was correct. That proof required the use of different techniques and led to our discovery of structures such as the one shown in the electron micrograph, in which DNA molecules were captured in the process of genetic recombination, using the Holliday intermediate.
Hope this helps you....
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