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(a) Drift and Selection
(a) Drift and Selection
What do you know about mutations?
What do you know about mutations?
Task 13
Task 13
Write down everything you can remember about mutations? What types of mutations are there and what are the consequences of mutation? Focus on the "benefits" of mutations. Explain how a DNA mutation can result in a phenotypic change.
The video opposite is a great starting point for this topic so sit back and relax while you take in the dulcet tones of Hank Green.
Evolution
Evolution
Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits.
During evolution, changes in allele frequency occur through:
the non-random processes of natural selection
the non-random process of sexual selection
the random process of genetic drift.
Natural Selection
Natural Selection
Natural selection acts on genetic variation in populations. Variation in traits arises as a result of mutation. Mutation is the original source of new sequences of DNA. These new sequences can be novel alleles. Most mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual.
This is a genuinely fantastic interview with Richard Dawkins explaining, with perfect concision, why natural selection is a NON-RANDOM process.
This is a genuinely fantastic interview with Richard Dawkins explaining, with perfect concision, why natural selection is a NON-RANDOM process.
Watch this quick YouTube video to observe the evolution of limbs, leading to the arrival of the first vertebrate animals on land.
Watch this quick YouTube video to observe the evolution of limbs, leading to the arrival of the first vertebrate animals on land.
Task 14
Task 14
"So natural selection is a process that leads to evolution?", posed Olivia. Big Davie was listening in, "Aye, like the more we all use our motors for wee trips, the more carbon dioxide we're pumping oot, the more acidic oor oceans are. So those alleles in marine organisms that are more tolerant of these changes in pH are more likely to survive."
Dr McRobbie listened on to the chat. There was no need to say anything more. "Continue your chats among yourselves and decide on a suitable example to explain the process of natural selection and evolution".
Suggested answers are here.
Take a few minutes to listen to this interesting example of evolution. It pays to be small in hot climates - a larger surface area:volume ratio means you can lose heat to your environment more efficiently; "Zebra finches will make a special call to their eggs in high temperatures, changing how fast they grow".
Sexual Selection
Sexual Selection
Sexual selection is the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring. Sexual selection may lead to sexual dimorphism.
Sexual selection can be due to male-male rivalry and female choice.
Male-male rivalry can lead to large size or weaponry, which can increase access to females through conflict.
Female choice involves females assessing the fitness of males.
Male-male rivalry (left) and female choice (right).
Genetic Drift
Genetic Drift
Genetic drift occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Genetic drift is more important in small populations, as alleles are more likely to be lost from the gene pool.
These images highlight the "random" nature of genetic drift.
It can be a one-off, unpredictable event that takes place, e.g. a fire, which does not select for those individuals with alleles conferring an advantage in the environment.
Instead, random alleles can be wiped out, leaving a group of individuals with, perhaps, disadvantageous alleles.
This can alter the genetic pool significantly, especially in small populations.
Task 15
Task 15
"That image there with the deer is a wee shame. He's a good looking fella but that deer only puts up with him because there are no other options in the end", empathises Kristie.
Dr McRobbie replied, "Well, Kristie, you are right. But actually think about how the random event that took place there will potentially have a big impact on future allelic frequencies. In your own notes, compare and contrast genetic drift, natural selection and sexual selection with regards to their influence on the course of evolution".
Kristie wishes she hadn't emphathised with the deer.
Here are some suggested answers if you also emphathised with the deer.
Causes of genetic drift
Causes of genetic drift
Watch and listen to the Amoeba Sisters video on Genetic Drift.
Watch and listen to the Amoeba Sisters video on Genetic Drift.
Founder Effects
Founder Effects
Click on the link opposite to hear about Founder Effects from the National Human Genome Research Institute. A couple of very useful, brief and clear videos about what founder effects are and the impact it has on evolution.
Task 16
Task 16
"Your old buddy Professor Dave is back Davie", announced Dr McRobbie. "Please use your understanding of the Founder Effect to explain the diagram opposite. What does it show and how does this impact evolutionary change? Professor Dave or the Amoeba Sisters might be able to help you here!".
Suggested answers can be found here.
Selection Pressures
Selection Pressures
Where selection pressures are strong, the rate of evolution can be rapid. Selection pressures are the environmental factors that influence which individuals in a population pass on their alleles. They can be biotic or abiotic, as outlined below.
Biotic
Biotic
competition
predation
disease
parasitism
Abiotic
Abiotic
changes in temperature
changes in light
changes in humidity
changes in pH
changes in salinity
The image above shows the effect of ocean acidification on coral reefs.
Task 17
Task 17
"Och Miss, I absolutely love that dude", announced wee Jonny.
"Jonny, you can't call Sir David Attenborough "dude"!" returned Dr McRobbie.
"He is a total dude Miss".
"Well, let's all watch this total dude and use the information to outline selection pressures faced by the iguana. What impact did this have on their survival?" - Dr McRobbie set her latest task.
See suggested answers here.
Hardy-Weinberg (HW) Principle
Hardy-Weinberg (HW) Principle
The Hardy-Weinberg (HW) principle states that, in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations – the conditions for maintaining the HW equilibrium are:
No natural selection
Random mating
No mutation
Large population sizes
No gene flow (through migration, in or out).
The HW principle can be used to determine whether a change in allele frequency is occurring in a population over time. Changes suggest evolution is occurring. You should be able to use the HW principle to calculate allele, genotype and phenotype frequencies in populations.
The article below provides some additional information to support your understanding of this area.
The article below provides some additional information to support your understanding of this area.
Did you get them correct? Were there any surprises? Add anything new that you learned to your Topic 2 notes.
Did you get them correct? Were there any surprises? Add anything new that you learned to your Topic 2 notes.
This is a great wee video to round off this section and leads nicely into the next. Before watching it, challenge yourself to consider what you think will be the 5 drivers of evolution.
This is a great wee video to round off this section and leads nicely into the next. Before watching it, challenge yourself to consider what you think will be the 5 drivers of evolution.
Ever wondered if humans are evolving? Well, of course we are. Find out how different mutations around the world have been selected for over a relatively short period of time in our own species.
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