Added folder #19

zsolt-balazs · 2020-02-17T10:41:51Z

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orisenbazuru · 2020-02-17T15:47:37Z

content/post/retrotransposons/index.md

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+Prior to the Human Genome Project, it was believed that humans had about a million genes. Today, we know that this number is somewhere around 25,000-35,000, depending on the definition. The terribly wrong estimate about the number of genes was based on the known size of the genome (3.2Gb) and the average size of genes (3-5kb). The false assumption, however, was that genes comprise most of our genome. After having sequenced the human genome, we know that the protein coding parts of the genes only take up about 1-2% of the genome. Even if we add the regulatory parts of the genes, we only explain the function of maybe 5-10% of the genome. The rest of the genome is frequently referred to as ["junk DNA"](https://en.wikipedia.org/wiki/Non-coding_DNA).
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+For most people, including myself, it is hard to digest that the majority of the DNA, the material that codes for all of our biology, is completely meaningless. In the past decades, we discovered that some of the sequences previously deemed junk DNA are actually important and play a role in maintaining the stability or the positioning of the chromosomes. Knowing this, it is easy to subscribe to the point of view that eventually, after we have understood everything about our genetics, we will see that all of what we considered junk DNA has a precise function are part of our genome for a reason. Nevertheless, there are several features of the genome that make one question whether the entire genome really has to make sense. Retrotransposons are such features. Retrotransposons are mobile elements of the genome which can "copy and paste" themselves into multiple parts of the genome. The way they do this, is quite simple: they have their sequence copied into RNA, then this RNA is reverse-transcribed into DNA which subsequently integrates into the genome. They are almost like little viruses replicating inside our genome. In fact, they share common features and in some cases common origins with endogenous retroviruses. Retrotransposons take up almost 50% of the human genome. Most of the retrotransposons are inactive either because mutations have eroded their functions or because the regulatory mechanisms of the organism keep them in check. Nevertheless, retrotransposons sometimes manage to create copies of themselves in our genome. When they do, they may contribute to cancer formation or they might disrupt the function of other genes. In some rare cases, the changes induced by retrotransposons may bring about changes that are beneficial to the organism. But in most instances, retrotransposons are detrimental or at best neutral. The most successful retrotransposon, the so called [Alu element](https://en.wikipedia.org/wiki/Alu_element), is found in over 1 million copies in the human genome.


just a nitpick: I think you can remove the comma in this sentence The way they do this, is quite simple:.
Otherwise, it reads well! 👏

zsolt-balazs

Thank you

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zsolt-balazs commented Feb 18, 2020

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zsolt-balazs merged commit 12bdac2 into master Feb 18, 2020

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Added folder #19

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zsolt-balazs commented Feb 17, 2020

orisenbazuru Feb 17, 2020

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		Prior to the Human Genome Project, it was believed that humans had about a million genes. Today, we know that this number is somewhere around 25,000-35,000, depending on the definition. The terribly wrong estimate about the number of genes was based on the known size of the genome (3.2Gb) and the average size of genes (3-5kb). The false assumption, however, was that genes comprise most of our genome. After having sequenced the human genome, we know that the protein coding parts of the genes only take up about 1-2% of the genome. Even if we add the regulatory parts of the genes, we only explain the function of maybe 5-10% of the genome. The rest of the genome is frequently referred to as ["junk DNA"](https://en.wikipedia.org/wiki/Non-coding_DNA).

		For most people, including myself, it is hard to digest that the majority of the DNA, the material that codes for all of our biology, is completely meaningless. In the past decades, we discovered that some of the sequences previously deemed junk DNA are actually important and play a role in maintaining the stability or the positioning of the chromosomes. Knowing this, it is easy to subscribe to the point of view that eventually, after we have understood everything about our genetics, we will see that all of what we considered junk DNA has a precise function are part of our genome for a reason. Nevertheless, there are several features of the genome that make one question whether the entire genome really has to make sense. Retrotransposons are such features. Retrotransposons are mobile elements of the genome which can "copy and paste" themselves into multiple parts of the genome. The way they do this, is quite simple: they have their sequence copied into RNA, then this RNA is reverse-transcribed into DNA which subsequently integrates into the genome. They are almost like little viruses replicating inside our genome. In fact, they share common features and in some cases common origins with endogenous retroviruses. Retrotransposons take up almost 50% of the human genome. Most of the retrotransposons are inactive either because mutations have eroded their functions or because the regulatory mechanisms of the organism keep them in check. Nevertheless, retrotransposons sometimes manage to create copies of themselves in our genome. When they do, they may contribute to cancer formation or they might disrupt the function of other genes. In some rare cases, the changes induced by retrotransposons may bring about changes that are beneficial to the organism. But in most instances, retrotransposons are detrimental or at best neutral. The most successful retrotransposon, the so called [Alu element](https://en.wikipedia.org/wiki/Alu_element), is found in over 1 million copies in the human genome.

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zsolt-balazs commented Feb 17, 2020

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