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Gene expression and function

Explore gene expression, the process where a gene synthesizes a product, often a protein. Discover how to determine a gene's function through knock-out experiments and reverse genetics, and learn about homologous sequences and their role in identifying gene functions.
Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video.
Created by Ronald Sahyouni.

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  • male robot donald style avatar for user Kashun Newson
    What if there are two different genes that make the same product? If you were to knockout one gene, wouldn't the other gene still function and produce the product?
    (8 votes)
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  • blobby green style avatar for user singhmana9
    At the end you say that when sequencing, you look for a homologous sequence. what is it homologous to though?
    (3 votes)
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    • female robot grace style avatar for user tyersome
      I agree that this could have been explained a bit more clearly ... the two sequences are homologous to each other.

      You have a gene sequence that you determined somehow (possibly you cloned the gene into a vector and then sequence the insert). You then compare that sequence with known sequences in a database and find a sequence that is similar (but not identical) to your new sequence. If someone has already learned what the gene in the database does, then you can infer that your gene is likely to do something similar.

      Does that help?

      Note, when two things are homologous means that they both descended from a common ancestor. In the case of DNA sequences this means that if trace the lineage of both sequences backwards at some point in the past the two sequences have a common ancestor sequence.

      Unfortunately homology/homologous is a frequently misused term. What most biologists mean when they say "homologous sequence" is actually just similar sequences — this often (but not always) means that the sequences really are homologous, but can be a bit confusing.
      (6 votes)
  • starky ultimate style avatar for user Jane Bartonjo
    When referring to reverse genetics () you said "start with the gene. How do you know what gene to start with? If you start with the gene then it means you already know the gene, is what we are trying to do here is to confirm the function of the gene? Or does one use other DNA technologies like microarray first to narrow down to some specific s before using reverse genetics?
    (4 votes)
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    • duskpin ultimate style avatar for user Becca
      Yes, pretty much it's just determining how the gene affects the phenotype . Due to the relatively low cost of whole genome sequencing, a lot of different organisms have been sequenced. Algorithms have been determined to predict regions that correspond to genes and other functional regions, as well as predict the family of protein regions code for if enough data from other organisms is available. However, this still needs to be confirmed experimentally, with knock out and knock in experiments and other methods of verifying the gene's function.
      (2 votes)
  • aqualine tree style avatar for user meenakshig097
    This was a really good video! But what does he mean when he says the gene has been 'knocked out?' I'm guessing when 'the gene is removed from the DNA?' I took it to mean 'knocked conscious' :-)
    (2 votes)
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  • marcimus pink style avatar for user horiandy lira
    how do we know which is the right gene to knock out
    (1 vote)
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  • blobby green style avatar for user adawg150
    whats the difference between mRNA, tRNA, rRNA
    (1 vote)
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  • piceratops seed style avatar for user Maria Corona
    What is Homologous Sequence ?
    (1 vote)
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Video transcript

- So what is gene expression? Well, it's basically the process where a gene is used to synthesize some sort of product. So you go from a gene to a product. And normally this product is a protein, but sometimes you can have non-protein coding genes. You can create things like ribosomal RNA, actually let's list these out. You can either have a protein, you can have ribosomal RNA, shortened to rRNA, you can have tRNA, tRNA, you can also have something known as small nuclear RNA. So basically you go from a gene to a product. Now, how do we determine what the function of the gene is? How do we determine a specific gene exactly what does it do? Well, let's imagine a scenario where there's a cell and normally it's able to if you give it milk... So lets imagine that we give it a bottle of milk, let me just draw a little bottle of milk, it's not the greatest bottle in the world, but, let's just imagine this is a bottle of milk, so we'll label that milk. So if you give this cell milk and normally it's able to take the milk and digest it and it's able to use the milk for energy. Well, what if we wanted to figure out what gene is responsible for being able to digest milk. Well, one thing that we can do is if we have an idea of what gene it might be we can just knock-out that gene. So let's just imagine that there's a gene here and we imagine that this has something to do with the digestion of milk. Well, if we knock it out and then we give milk to the cell and if it's still able to digest the milk then we know that this gene didn't really have much to do with digestion of milk. But if we knock it out and the cell is no longer able to digest the milk, then we know that this gene had something to do with the digestion of milk. So this process is known as a knock-out. So basically, you're knocking out a gene and trying to figure out what the function is of the gene. So if you knock out a gene what happens to the organism? So you basically create a knock-out mutiny and study its effects. So another thing you can do is something known as reverse genetics, reverse genetics. So here what you do is first you start with a gene, and then you sequence it. You figure out what is the sequence of the gene. And then what you can do is you can look for other gene sequences somewhere else in the genome that share a similar sequence. So you sequence it and then you look for a homologous sequence somewhere else in the genome. And if you know what that homologous sequence does then you have a pretty good idea of what that gene might do. So if you know that there's this homologous sequence somewhere else in the genome and it goes for a specific protein, and you know the function of that protein, then you know that the gene of interest might create a protein that has a similar function.