Variation Caused by Recombination and Crossing over
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Variation Caused by Recombination and Crossing over

Readers will gain a simple, but to the point understanding of two sources of variation. The process of recombination is explained with a relatable, and easy to imagine example. Additionally, crossing over is also explained concisely for an easy and understandable read. Both processes happen within the S phase of the cell cycle, which is the phase where the cell’s DNA is being replicated.

One repeated trend in biology is variation. It is especially intriguing because one organism can express different phenotypes caused by mutation in a single gene. Variation arises as a result of processes called recombination and crossing over, which is the topic of this work. However, it should also be noted that variation also results from mutation, having more to do with error in nucleotide base-pairing rules. Moreover, the process of how crossing over and recombination happen in a specific stage of the cell known as the S phase. The S phase denotes the synthesis of DNA and it is at this stage where DNA is being replicated in a cell. Additionally, it is in the S stage where DNA is able to recombine and undergo the process of crossing over.

The process of recombination can be simply described as the process in which alleles of the same gene get separated into different gametes. Recombination ensures that each gamete gets one allele from the same gene. To highlight the concept of recombination, we can think about it as distributing gift cards to all students in a class, for example. All of the students are receiving a gift card, but not to the same store. Instead, all students receive a gift card to different stores. Similarly, recombination ensures that all gametes get an allele of the same gene, but that may encode a different genotype.

Next to be covered is the process of crossing over. Generations of a single family, for example, will pass down similar characters, such as eye color and hair color. Variation amongst a family occurs through the process of crossing over. In this case, genes physically exchange DNA information originating at a place in the chromosome called the chiasmata. The chiasma is the location where homologous non-sister chromatids are physically connected to prepare the exchange of DNA content. Crossing over occurs in a process called meiosis, which is when the cell is preparing for cell division.  After exchange of DNA content has occurred, there are different variations of the same alleles being transferred to the next gametes. This is one of the reasons that siblings, though they might obtain DNA content from the same parents, can look very different, or for that matter, look alike.

To conclude, variation is a form of contributing different traits to the offspring of organisms. It is a result of various processes, two of which include recombination and crossing over. Recombination assures that each gamete receives an allele from a gene, where as crossing over is the process of mixing the alleles in homologous non-sister chromatids.  

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