Natural selection
What is an allele?
different form of a gene
What is genetic drift?
change in population's allele frequency due to random occurences/chance
What is gene flow?
Flow or movement of alleles in and out of a population's gene pool
What is selective breeding?
Selective breeding: the changing of a population’s gene pool due to humans altering the breeding behaviour of animals and plants for a selected trait
What is evolution?
The change in genetic makeup of a population over generations
Two ways genetic drift can occur
Bottleneck and founder's effect
3 possible ways gene flow might occur
Emigration Immigration Interbreeding
3 requirements of artificial selection
Variation (phenotype and genotype) must be present in the population
Human intervention places an artificial selection pressure on the population, only allowing individuals with the desired trait to reproduce
The desired trait must be heritable (passed down from parents to offspring)
Define fitness in the context of evolution
How well an organism survives and reproduces in its environment
Compare and contrast genetic drift from natural selection?
Natural selection is based on a selection pressure and alleles increase or decrease based on selective advantage they confer, while in genetic drift the allele frequency changes based on random chance.
Which one increases genetic diversity in a population, inbreeding or interbreeding? Explain your answer
Interbreeding would increase genetic diversity
as the immigrating individual carries unique alleles with them and breed with local population in contribute those alleles to the gene pool
Inbreeding is the reproduction between genetically closely related individuals which decreases genetic diversity (increase homozygosity and overexpression of deleterious alleles)
Why is inbreeding risky for an organism? Explain using dominant and recessive alleles.
inbreeding increasing the homozygosity of recessive deleterious traits of the population leading to higher expression of these deleterious traits. These recessive traits are normally masked by dominant alleles.
What are the four conditions required for natural selection to take place?
Variation (in genotype and in phenotype)
Selection pressure
Selective advantage
Heritability of traits
What is the difference and similarities between the bottleneck effect and the founder effect?
Both lead to small populations (that is likely to have an unrepresentative allele frequency of the original population).
Bottleneck: a large proportion of the population is wiped out by a random occurrence
Founders effect: small group of individuals separates from a larger population in a new environment
How does gene flow help or counteract the effects of genetic drift or natural selection?
gene flow can counteract the effects of small population size by increasing effective pop size in immigration and interbreeding
Make it worse if there is emigration.
In immigration, introducing alleles also help increase genetic diversity which may help in adaptive potential to changing environments
How does artificial selection affect genetic diversity?
Selective breeding can lead to reduced genetic diversity as there is smaller gene pool (due to human induced bottleneck)
bad breeding practice leads to more inbreeding → overexpression of deleterious alleles and reduces adaptive potential for a population
Does changes in environmental conditions affect the genetic diversity of a gene pool?
Yes, it can reduce the genetic diversity of a gene pool if alleles that confer selective advantage are more likely to be found in the gene pool compared to before the change
Explain the disadvantages of small population size (reference genetic drift and diversity)
Small population size is likely to have lower genetic diversity, this can
increase the populations' susceptible to the effects of genetic drift (e.g., in the case of bottleneck of founders effect), increasing the risk of fixing a particular allele for example, this can also
Increase risk of extinction due to lowering adaptive potential and
Increase risk of inbreeding (increases risk of overexpression of deleterious alleles)
A small group separated from another large population to occupy a new environment with different living conditions. Explain what would happen to the old population (referencing gene flow)
Old population's genetic diversity might decrease due to having alleles leaving the population however the effects are most likely negligible due to the large population size.
Evaluate the following statement: Organisms from selective breeding is the same as GMO (genetically modified organism).
Possible answer:
Both selective (traditional) breeding and modern genetic engineering produce genetic modifications, and thus artificial selection is a form of genetically modification (but more population wide)
Selective breeding takes multiple generations of careful selection to breed individuals however new genetic modification could be done on single individuals or their direct offsprings.
Black peppered moths are a classic example of natural selection. Explain the evolution of the peppered moth towards the black variant using the 4 factors of natural selection.
Peppered moths' population had two main phenotypes (black and white) which are caused by genetic variation between individuals
Environmental changes due to pollution during the industrial revolution change the colours of trees that the moths are found on, and predatory birds eat moths that are more visible.
Dark peppered moth had a selective advantaged in this altered environment as they are less likley to be seen and eaten by predators, and are more likely to survive and reproduce.
Since the trait is heritable (encoded in the genome), over many generations, the dark peppered moth phenotype frequency will increase in the population
A small group separated from another large population to occupy a new environment with different living conditions. Explain the effects on the new population.
New small population is an example a founder effect, they are more susceptible to genetic drift as they might be a sample that is not representative of the original population, this could lower genetic diversity, increase risk of inbreeding, lower adaptive potential (especially since they are in a new environment which may different selective pressures)
Explain how gene flow has contributed to the prevalence of lactose tolerance in different human populations across the globe.
Gene flow has contributed to the spread of lactose tolerance by introducing the allele for lactase persistence into various populations. This allele allows individuals to digest lactose into adulthood, providing a nutritional advantage in societies where dairy farming is prevalent. The evolutionary significance lies in how cultural practices (dairy farming) have influenced genetic evolution, with gene flow facilitating the spread of advantageous alleles across different populations, enhancing their ability to exploit new food resources
Explain how selective breeding in agriculture has led to the development of monocultures (growing only a single crop type) and discuss the risks associated with this practice
When a single crop variety is grown extensively (and there is low genetic diversity between the individuals of the crop population), this could increase vulnerability to pests and diseases and environmental changes (low adaptive potential). Additionally, monocultures can lead to soil depletion and threatens food security.