Impact of Natural Selection on Population Size

I have conducted a lab with my IB Biology 11 class, regarding changes in allele frequencies within generations overseeing the natural selection of an advantageous phenotype. We were looking to conclude some sort of link between the changing allele frequencies and an overall changing population number of the species. Lab results saw, that as the frequency of the advantageous phenotype increased, the total population dipped and then increased after the 3rd generation. Can anyone point out any possible reasons as to why this occurred - regarding any factors at all? The image below depicts frequency of the advantageous allele vs total population.

• Can you give more detail because I don't understand? Was this an experiment or a simulation? What was the advantageous phenotype and did you know in advance that it would be advantageous ? In your graph, what is on the x axis and what is on the y axis? – sterid Apr 15 '18 at 14:17
• @remi.b Can you provide some illumination? I don't understand it. – sterid Apr 16 '18 at 2:16
• @JohnnyToff The question is unclear to me. Your picture does not contain any axis labels, you talk about both population size and allele frequency but I don't understand what connection you're making in between them and I do not understand exactly the pattern you've observed. If you're dealing with population, it is also unclear the population dynamic before the introduction of a mutation and it is unclear whether the mutation was beneficial or deleterious. I am voting to close as unclear. – Remi.b Apr 16 '18 at 17:14
• You should always label axes on a graph. I know it's explained in the text, but it's best practice to label your graphs to facilitate understanding of the data you're presenting. – oldchemist May 10 '18 at 18:59
• Related: xkcd.com/833 – Bryan Krause May 10 '18 at 20:00

1 Answer

This is pretty basic, should have learned it in year one bud, but, here... everyone should be able to decipher this.

You can also use Calculus to solve this.

Edit: The dip was most likely because natural selection often has a bit of a delay until it becomes advantageous to the population. Otherwise, the increase should continue if you go on to further generations.

• What are w, w2 and w3? – sterid Apr 15 '18 at 14:19
• The sentence natural selection often has a bit of a delay until it becomes advantageous to the population is at best unclear, at worst flat wrong. -1 – Remi.b Apr 16 '18 at 17:08
• @Theodore I thought the question had to do with population size and not only with change in allele frequency but I don't understand the question. The answer does not mention population size (and actually assume it is infinite). The sentence You can also use Calculus, but I'm guessing you can't. could be taken as offensive. Please be cautious of how you communicate esp. when you really have no idea of the math skills of the OP. – Remi.b Apr 16 '18 at 17:09
• Also, please do not post text as images. Images are not searchable and it can be unpleasant to read text from an image. Also, please indicate your source, esp. when you cite some text you have not written yourself. – Remi.b Apr 16 '18 at 17:12
• Please do not use images for text. Please try to type the equation out using LaTeX and provide the reference. We can help you with that if you need it. – WYSIWYG Apr 20 '18 at 11:57