How does chromosomal crossing over occur in tightly wound DNA?

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In summary, the conversation discusses the process of chromosomal cross over and the difficulty in understanding how DNA can be cut and rejoined when it is tightly packaged in chromosomes. It is explained that the chromatin DNA must unwind in order for recombination to occur.
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Yuqing
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In most of the books I've read, chromosomal cross over has been described as simply "segments of the chromosome breaking off and reattaching", but I have a bit of difficulty with this explanation. Chromosomes are densely packaged DNA that have been wound and wound again. How can DNA which has been so tightly wound and packaged be cut and rejoined so simply? Most of the searches of the recombination process shows recombination occurring between two simple strands of DNA which should not be accessible when DNA is packaged as chromosomes. Does the chromosome uncondense at the part crossing over in order to recombine?
 
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The short answer is yes, the chromatin DNA must unwind from its nucleosome-bound state in order to engage in homologous recombination.
 

1. What is chromosomal crossing over?

Chromosomal crossing over is a process during meiosis where homologous chromosomes exchange genetic material, resulting in new combinations of genes being passed down to offspring.

2. Why does chromosomal crossing over occur?

Chromosomal crossing over occurs to increase genetic diversity within a population. This process allows for the creation of new combinations of genes, increasing the chances of survival and adaptation.

3. How does chromosomal crossing over contribute to genetic variation?

Chromosomal crossing over creates new combinations of genes, increasing the genetic variation within a population. This allows for a wider range of traits and characteristics, making a species more adaptable to changing environments.

4. Can chromosomal crossing over result in genetic disorders?

In some cases, chromosomal crossing over can result in genetic disorders if there is an error in the exchange of genetic material. This can lead to the duplication, deletion, or rearrangement of genes, causing genetic disorders such as Down syndrome.

5. How is chromosomal crossing over important in evolution?

Chromosomal crossing over plays a crucial role in evolution by creating new combinations of genes that can be passed down to offspring. This allows for the development of new traits and characteristics, which can increase the chances of survival and reproduction in a changing environment.

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