Flashcards for AQA A Level Biology Chapter 18- Populations and Evolution
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Course
Chapter 18- Populations and Evolution
Institution
AQA
Contain all you need to know for this chapter of the course. Are detailed and concise, and work best with Anki, but can be used with quizlet. They are in the form of a txt document that can be imported into anki or quizlet. Some images are missing due to the format, so these images will have to be ...
What is a gene pool? All of the alleles of all the genes of all of the
individuals in a population
What is the allelic frequency? The amount of times an allele appears in the
gene pool
What are the two Hardy-Weinberg principle formulae? Let the probability of allele
A = p and the probability of allele a = q<div>p + q = 1</div><div>p<sup>2</sup> +
2pq + q<sup>2</sup> = 1</div>
What are the assumptions Hardy-Weinberg makes? No mutations arise<div>The
population is isolated so there is no gene flow in or out of the
population</div><div>There is no selection </div><div>The population is
large</div><div>Reproduction within the population is random</div>
What are the two main types of causes of variation? Genetic and environmental
What are the four main reasons for genetic variation?
<div>Mutation</div><div>Independent assortment</div><div>Crossing
over </div><div>Random fertilisation of gametes</div>
What is the natural selection process? A population exists in an environment,
and that environment has its own selection pressures<div>There is variation in that
population due to mutations</div><div>Some individuals in the population will have
an advantageous phenotype and allele that allows them to outcompete the other
individuals in their species</div><div>As such, these advantaged organisms are able
to pass their advantageous allele onto the next generation more easily as they are
more likely to survive and reproduce</div><div>As such, the allelic frequency of
this advantageous allele increases</div>
What does stabilising selection look like? "<img src=""image-
108703ef4a805fb57385e9d48c5a6f5602174e90.png"">"
What effect does stabilising selection have on evolution? It eliminates the
extreme phenotypes
When does stabilising selection occur? When the environment stays constant
What does directional selection look like? "<img src=""image-
9504a5171961eb7cf3f1510982da76975388a7fd.png"">"
What effect does directional selection have on evolution? The frequency for the
phenotype favoured by the new environment will increase
When does directional selection occur? When there is a change in environment
What does disruptive selection look like? "<img src=""image-
90ff17f3e1e3731b9f8b595d5060774686b35f06.png"">"
What is the effect of disruptive selection on evolution? The frequency of extreme
phenotypes increases and the frequency of intermediate phenotypes decreases
When does disruptive selection occur? When a selection pressure takes up two
forms, like temperature
What is the condition for speciation to occur? Two populations are reproductively
isolated and there is no gene flow between the two
When is speciation said to have happened? When the two separated populations are so
different that they can no longer breed together to produce fertile offspring
Why is genetic drift more prevalent in smaller populations?In a small population,
there is a lower genetic diversity, meaning there are fewer alleles. As such, those
that arise have a high chance of being passed on and spread throughout the
population quickly, accelerating speciation
What is allopatric speciation? When the two populations are geographically
isolated by some kind of physical barrier, like a river. The environment will vary
between the two sides of the physical barrier, causing different alleles to be
selected for in each environment
What is sympatric speciation? When two populations are reproductively separated but
not geographically separated, meaning speciation still occurs
What is genetic drift definition wise? Changes in allele frequency in the gene
pool of a population due purely to chance events and not selection pressure
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