Genetic Change
Learning intention: To develop an understanding of genetic change
Success criteria: Discuss how genetic change occurs in a gene pool (microevolution)
Embedded Files
What can cause a change in a gene pool?
What can cause a change in a gene pool?
What we mean by a gene pool and allele frequency?
What we mean by a gene pool and allele frequency?
Watch the video , then write your definition in your note book - remember to use your external Biozone book to solidify your learning
What we mean by gene flow?
Watch the video , then write a definition in your note book
Define population
Watch the video , then write a definition in your note book
In this chapter we will learn about the processes that can cause changes in the allele frequency of a gene pool.
Processes that can change the allele frequency of a population
Processes that can change the allele frequency of a population
Processes that can change the allele frequency in a population include:
Mutation
Natural selection
Genetic drift (founder and bottleneck effect)
Gene flow or migration
Natural Selection
Natural Selection
Natural selection is the process by which there is selection for and against certain phenotypes over time due to competition, and because of this differential survival and therefore reproduction.
This means that different alleles will also be selected for and against, causing allele frequencies to change over time. It works like this:
ACTIVITY: Watch the video and complete the worksheet.
ACTIVITY: Watch the video and complete the worksheet.
Natural selection worksheet.pdfMigration and Gene Flow
Migration and Gene Flow
Migration is the movement of individuals into (immigration) or out of (emigration) of a population gene pool. Depending on whether the movement is one way or two way changes the effect on allele frequencies.
If one way into the gene pool new genetic information may be introduced increasing allele frequency, and if one way out of the gene pool genetic information may be lost reducing allele frequency.
On the other hand if two way, the overall net outcome can be no change to allele frequency as individuals both move into, and out of, the gene pool.
Because individuals carry the genetic information or genes into and out of the population this is called gene flow. It ensures that the populations maintain similar gene pools! So only if populations are isolated do they then have the potential of different phenotypes being selected for or against, and their direction of evolution becomes different.
ACTIVITY - Gene flow review
ACTIVITY - Gene flow review
Summarise the process of gene flow and its effect on allele frequency in the gene pool
Genetic Drift
Genetic Drift
Genetic drift is a random change in allele frequencies.
It is caused by alleles increasing and decreasing over time by chance.
It can, therefore, both increase and decrease genetic variation, and even cause rare alleles to increase and even become fixed, or prevalent in the population.
There are two major types of genetic drift that may occur in populations:
The Bottleneck Effect - where a populations size becomes small very rapidly.
The Founder Effect - where a few individuals in a population colonize a new location that is different to the original population.
ACTIVITY: Use the table to compare and contrast the two types of genetic drift below.
In the example to the right, you can observe the effect of genetic drift over three generations of rabbits. From this you can see how it can lead to the elimination of an allele from a population by chance.
Rabbits with brown coat (B) are dominant to rabbits with a white coat (b)
In the first generation, the two alleles are equal in the population. However, only half of the rabbits reproduce.
Further, only two individuals in the second generation reproduce and by chance these are the rabbits that are homozygous dominant for brown coat colour.
This means that in the third generation the recessive (b) allele is lost from the population.
So, by chance, a few individuals leave behind a few more descendants than other individuals. It's just luck not a matter of fitness and this happens in all populations!
ACTIVITY: Watch the video and complete the worksheet.
ACTIVITY: Watch the video and complete the worksheet.
Genetic drift worksheet.pdfPopulation Size Matters!
A small population size reduces the genetic variation of the population. They are more susceptible to change due to this and therefore at risk of extinction. This is because alleles are more likely to be lost due to chance and this is more likely when they are small. This is even more true where small populations are also inbreeding - or there is mating between closely related individuals - alleles are likely to become fixed, ie. only one of the alleles remain.
This is why breeding programs, for example at zoos, work to increase genetic variation. They do this through the manipulation of the gene flow or migration of new individuals into and out of a breeding program to ensure genetic variation in a species and increase their change of survival.
The Sumatran tigers at Auckland Zoo have been bred together. Baby tigers coming in late 2023!!
Biozone Activities
Biozone Activities
E86 Processes in gene pools, p 121
E87 How natural selection works, p 123
E88 Types of natural selection, p 125
E92 The founder effect, p 131
E93 Population bottlenecks, p 133
E94 Genetic drift, p 135
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