Mutations & Pesticide Resistance

Amy Hauver Author

07/19/2022 Added

31 Plays

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A summary of two types of genetic mutation (frameshift and point mutation) and how the mutation can impact trait expression. Mutations are learned through the lens of pesticide resistance.

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[00:00:10.467]In this video, you'll be learning about
[00:00:12.717]the different major types of mutations
[00:00:15.117]and how they are one of the origins of pesticide resistance.
[00:00:19.437]Mutations occur at very low rates naturally,
[00:00:23.067]and are selected for when they're beneficial to survival.
[00:00:26.847]Rare mutations may end up being beneficial
[00:00:29.277]when it provides an organism like a plant
[00:00:31.647]with a selective advantage in an environment.
[00:00:34.827]If plants that have the resistance allele
[00:00:36.837]survive to produce more offspring,
[00:00:39.297]the resistance allele becomes
[00:00:40.647]more common in that population.
[00:00:43.377]So what is a mutation?
[00:00:45.657]A mutation is a change in DNA.
[00:00:48.057]It creates new alleles
[00:00:49.467]which are slightly different versions of the same genes.
[00:00:52.467]It's completely spontaneous, mutations happen randomly,
[00:00:56.397]and they occur for several reasons.
[00:00:58.617]The DNA can fail to copy accurately during mitosis,
[00:01:03.027]the DNA can fail to transcribe correctly,
[00:01:06.357]RNA can fail to translate correctly into a protein,
[00:01:10.707]and there are also external influences
[00:01:13.767]that can create mutations like UV radiation from the sun.
[00:01:19.677]The types of mutations can be broken down
[00:01:21.987]into their impact on DNA and proteins.
[00:01:25.047]Frameshift and point mutations impact the DNA,
[00:01:28.767]and point mutations can further be categorized
[00:01:31.347]into how they impact the protein.
[00:01:33.897]There's missense mutations,
[00:01:35.667]silent mutations, and nonsense mutations.
[00:01:40.647]First we'll talk about frameshift mutations.
[00:01:44.637]Frameshift mutations occur in the DNA.
[00:01:47.637]On the left side of this table is the unchanged
[00:01:50.397]trait expression process before mutation occurs.
[00:01:54.147]In a frameshift mutation,
[00:01:55.947]a nucleotide is either added or deleted
[00:01:58.257]from the DNA sequence during replication.
[00:02:01.467]This means the entire frame that is read
[00:02:03.657]is shifted over to account for this addition or deletion.
[00:02:07.797]In this case, an extra adenine is added in the DNA sequence.
[00:02:12.747]When the DNA is transcribed into messenger RNA,
[00:02:15.717]the extra nucleotide is also transcribed.
[00:02:18.657]So far, no obvious big change has occurred,
[00:02:22.197]but when the time comes for the messenger RNA
[00:02:24.537]to be translated into the protein,
[00:02:26.697]the three nucleotides that make up a codon
[00:02:29.517]no longer match up as they did
[00:02:31.167]before the frameshift mutation occurred.
[00:02:33.717]This means that a different amino acid
[00:02:35.757]or a series of amino acids will be added to the protein.
[00:02:39.297]This can result in an altered protein
[00:02:41.307]that no longer functions as it was meant to.
[00:02:46.557]DNA point mutations result from a single nucleotide
[00:02:49.887]being replaced with a different nucleotide.
[00:02:52.617]A reading frame shift does not occur
[00:02:54.747]since the nucleotide is only replaced,
[00:02:57.447]and nothing more is added or deleted.
[00:02:59.997]Point mutations can be classified as missense,
[00:03:02.577]silent, or nonsense point mutations,
[00:03:04.797]depending on how the change is expressed
[00:03:07.137]in the amino acid sequence of the resulting protein.
[00:03:12.267]A missense mutation will cause a change
[00:03:15.237]in a single amino acid,
[00:03:16.737]but the impact on the subsequent protein will be minimal.
[00:03:20.457]For example, during DNA replication
[00:03:22.977]let's say the nucleotide cytosine
[00:03:26.727]has been replaced with the guanine.
[00:03:29.037]When the DNA is transcribed,
[00:03:30.597]the guanine is transcribed
[00:03:32.847]which is translated into a new amino acid.
[00:03:36.447]Since it is only a single amino acid change,
[00:03:38.967]there will not likely be a large change
[00:03:41.637]in the final protein.
[00:03:43.587]It may cause a structural change,
[00:03:45.477]but it is unlikely to change
[00:03:46.977]the enzyme's ability to function.
[00:03:50.307]Second type of point mutation is a silent mutation.
[00:03:54.087]A silent mutation results in no real change
[00:03:56.787]in the amino acid sequence or the protein.
[00:03:59.547]In this example, the nucleotide thymine
[00:04:02.067]has been replaced with the cytosine in the DNA.
[00:04:05.187]And after being transcribed and translated,
[00:04:07.437]the resulting change is the same valine amino acid.
[00:04:11.307]This means that there is no real change in the protein
[00:04:14.067]and it goes undetected.
[00:04:17.367]The last type of point mutation we will discuss
[00:04:19.587]is the nonsense mutation.
[00:04:21.957]When a nonsense mutation occurs,
[00:04:24.057]it creates a stop codon,
[00:04:27.627]resulting in the protein being prematurely terminated.
[00:04:30.927]This can mean you only get a portion of the protein,
[00:04:34.377]or there's no protein at all
[00:04:35.997]if the stop codon occurs early.
[00:04:41.307]Now that we've discussed the types of mutations
[00:04:43.317]that can affect an organism,
[00:04:44.847]we can use them to understand
[00:04:46.287]how they can lead to pesticide resistance.
[00:04:49.197]Pesticides use target sites like proteins and enzymes
[00:04:52.077]to inhibit critical functions and essential processes.
[00:04:55.767]Since mutations can act to change
[00:04:57.627]these target sites on the proteins
[00:04:59.787]that the proteins and enzymes still perform their processes
[00:05:03.327]but impedes the efficacy of a pesticide,
[00:05:05.997]since it is no longer able
[00:05:08.097]to bind to inhibit their function.
[00:05:10.707]Mutations can also change
[00:05:12.087]the expression level of essential enzymes,
[00:05:14.727]either amplifying the gene that codes for them
[00:05:17.337]or causing overexpression so that it overcomes
[00:05:19.977]the pesticide's ability to inhibit.

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Mutations & Pesticide Resistance

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