Allele Frequency Changes: Mutation and Selection

Amy Hauver Author

07/20/2022 Added

61 Plays

Description

This video details the impact of mutations and selection on allele frequencies for various pesticide resistant populations.

Searchable Transcript

Search:

[00:00:09.960]In this video,
[00:00:10.950]we'll be discussing two of the four
[00:00:13.170]forces that affect the gene pool,
[00:00:15.690]mutations and selection.
[00:00:18.720]As we discussed in the first video in this module,
[00:00:22.200]a gene pool is a population of interbreeding individuals,
[00:00:25.620]and is the collection of all of the alleles
[00:00:27.780]and of all of the genes found
[00:00:29.550]within that inter breeding population.
[00:00:32.670]Each member of the population inherits alleles
[00:00:35.370]from other members of the gene pool.
[00:00:37.620]And these are the parents in that population.
[00:00:40.170]And they pass them on to other members of the gene pool.
[00:00:42.990]And these are the offspring of the population.
[00:00:46.350]There are many forces that affect and cause changes
[00:00:48.780]in the allele frequencies in a gene pool,
[00:00:51.240]but we will discuss four of them.
[00:00:53.280]In this first video,
[00:00:54.510]we'll be talking about mutation and selection.
[00:00:57.090]And in the second video,
[00:00:58.230]we'll discuss migration and drift.
[00:01:01.590]Mutations are changes in the DNA,
[00:01:03.600]and they create new alleles from the current genes.
[00:01:06.540]It occurs spontaneously, and in the population,
[00:01:09.480]and it may or may not have an effect.
[00:01:14.310]You can see here in A, there's a population of plants.
[00:01:17.790]And in B, you can see that these alleles are all the same.
[00:01:21.390]in C, a mutation occurs,
[00:01:23.130]and there is now a new allele present in the population.
[00:01:25.950]And in D, you can see the allele frequency change
[00:01:28.860]due to the presence of a new, more suitable gene.
[00:01:33.960]This is a sample population of Colorado potato beetle,
[00:01:37.110]which is a pest of most members of a Solanaceae family,
[00:01:40.590]such as potato, tomato, pepper, eggplant, and weeds,
[00:01:44.100]such as nightshades and buffalo bur.
[00:01:47.310]It has been known to defoliate entire potato fields
[00:01:49.710]in North America.
[00:01:51.900]The Colorado potato beetle has developed resistance
[00:01:55.050]to a number of insecticides, and an overexpression
[00:01:57.720]of a cytochrome P450,
[00:01:59.550]which is this detoxification enzyme,
[00:02:02.130]is associated with many of these resistants,
[00:02:06.810]imadocloprid resistance being a major one.
[00:02:10.890]The Colorado potato beetles' resistance to imadocloprid,
[00:02:14.370]caused by the overexpression of cytochrome P450
[00:02:17.610]could be compared to palmer amaranth's resistance
[00:02:19.890]to glyphosate.
[00:02:21.180]In palmer amaranth, there's an amplified number of the genes
[00:02:24.090]that produce the EPSP synthase enzyme
[00:02:26.460]that creates essential amino acids.
[00:02:28.830]We talked more about this in module one's first video.
[00:02:32.940]In the Colorado potato beetle, there's a similar phenomenon
[00:02:36.240]of an increased amount of an enzyme,
[00:02:40.620]but it all comes from the original single gene.
[00:02:45.840]Instead of having many genes creating one enzyme
[00:02:48.210]causing resistance,
[00:02:50.100]Colorado potato beetle has a single gene
[00:02:52.470]that is upregulated.
[00:02:54.060]This upregulation causes an overexpression
[00:02:56.460]of the enzyme, dramatically increasing its
[00:02:58.740]ability to detoxify insecticides, like imadocloprid.
[00:03:04.650]Selection is the preferential survival
[00:03:06.780]and reproduction of an individual in a population.
[00:03:10.380]Preferential survival and reproduction is due
[00:03:12.930]to different genotypes and their interaction
[00:03:15.030]with the environment.
[00:03:16.830]In image A, there is another population of plants.
[00:03:20.160]In B, you can see the two different genotypes,
[00:03:22.800]the pink and the green.
[00:03:24.690]If the pink represents the plant's ability
[00:03:26.880]to detoxify a herbicide application,
[00:03:29.580]then when the selection pressure
[00:03:30.900]of a herbicide application is applied,
[00:03:33.120]they will be able to survive to reproduce.
[00:03:37.560]For an example on selection acting towards
[00:03:39.990]changing the gene pool and leading to resistance,
[00:03:42.630]we'll use wheat leaf rust,
[00:03:44.430]a fungal disease that affects wheat, barley and rye.
[00:03:47.880]Let's say a producer goes out in the field
[00:03:49.770]and sees this first image.
[00:03:51.810]To protect the yield of his crop,
[00:03:53.790]he applies a fungicide,
[00:03:55.620]like a Azoxystrobin to control the rust.
[00:03:58.440]This application gives good control
[00:03:59.870]of the fungus, with only a few escapes.
[00:04:09.750]Most escapes are caused by a level of misapplication,
[00:04:12.690]but there also can be some individuals
[00:04:14.640]in the population that have standing resistance.
[00:04:17.310]This means that the gene that contributes
[00:04:19.080]to resistance is already present
[00:04:22.050]in some individuals in a population.
[00:04:24.300]And it is a matter of selection for the population
[00:04:26.820]to become resistant.
[00:04:29.490]I've highlighted one of the individuals here
[00:04:31.440]that escaped and carries the resistance gene.
[00:04:34.350]These spores are transported via wind
[00:04:36.570]to surrounding hosts,
[00:04:37.680]along with new spores from other populations.
[00:04:40.860]These spores land
[00:04:41.970]and they germinate and produce a new colony,
[00:04:46.980]this time with more resistance genes in the population,
[00:04:50.910]which I've also highlighted.
[00:04:52.740]Because the grower got such good control
[00:04:54.720]the first time applying Azoxystrobin,
[00:04:56.970]they used it again.
[00:04:58.620]This time they seemingly get good control again,
[00:05:01.410]but there are still escapes in the population,
[00:05:03.780]with many of them carrying the resistance allele.
[00:05:06.960]These spores are blown to a new host and reproduce,
[00:05:10.590]forming a population that has more resistance.
[00:05:14.580]If this grower uses azoxystrobin again,
[00:05:17.220]they're likely to have a much less control
[00:05:19.470]and eventually the product will fail.
[00:05:26.610]This population of rust has standing variation,
[00:05:29.520]the collection of all of the alleles present
[00:05:31.620]in the gene pool.
[00:05:33.090]This occurs when random mutations create new alleles.
[00:05:37.440]At the time of creation,
[00:05:38.910]these alleles have no selective advantage
[00:05:40.920]in the current environment
[00:05:42.210]where there is selection pressure applied to them.
[00:05:45.240]This means there's also no disadvantage
[00:05:47.430]to the creation of the new alleles.
[00:05:49.020]They are just simply present.
[00:05:51.120]These seemingly useless new alleles
[00:05:53.010]caused by random mutations may be necessary
[00:05:55.980]for genes to create a pesticide resistance
[00:05:58.800]under the correct selection pressure.

The screen size you are trying to search captions on is too small!

You can always jump over to MediaHub and check it out there.

Comments

0 Comments

Allele Frequency Changes: Mutation and Selection

Description

Searchable Transcript

Comments icon comment

Related Channels

Comments