3.4 Selection: Change in gene- and genotype frequencies by selection

You can start either real observations (numbers) or relative genotype frequencies in the relevant fields.

Gene frequency p ->
Gene frequency q -> Generations ->
Set digit for print ->
Generation q Frequency Genetic load           ........ Change of q (1) and load (2) over generations ......

Click the Calculate button. Put the fitness of the genotypes (relative or numbers, e.g. the heterozygote can have values above 1) you set the number of generation, if you want more than one; or you can get a graph over gene frequency changes over the generations you want by chosing the number of generations. The corresponding data you can extract over the clip board in the lower left window.
You can also start the process by putting your gene frequencies and there after take some selections rounds.
For practical reasons delta q is put to 0 for values less than .000001. Sometimes when delta q is less than .0001 there are problems with rounding and some browsers can not see the results proper.


If you have a genetic system for instance yellow coat colour in the Labrador Retriever, where the recessive (yellow) have the fitness 1-s by selection you get:

Genotype         EE  Ee  ee Total
Observed number  141    80    11     = 232
Frequency         p2   2pq    q2     = 1.00
Fitness           1     1     1-s
Proportion        p2    2pq    q2(1-s) = 1-sq2
after selection
After selection the gene frequency q' can be calculated by the gene counting method, q' is the gene frequency in the next generation, is calculated as half of the heteroygotes plus the surviving recessive relative to half of the proportion of all surviving genes, that is equal 1-sq2.
      q' = (2pq/2 + q2(1-s))/(1-sq2)
To test the program put the observed number and press the Calculate button. You then get q=0.2198, if you have s(aa)=0 and press the +1 generation button you get q'=0.1802.
Calculate the gene frequency in the first 5 generations of selection and the equilibrium gene frequency in the genetic system shown below with selection favouring the heterozygotes with s1 = 0.3 and s2 = 0.5

Genotype         AA               Aa             aa       Total
Observed numbers 225		  157            43
Frequency        p2               2pq            q2       = 1,00
Fitness          1-s1              1            1-s2      
Proportion       p2(1-s1)         2pq           q2(1-s2)   = 1-p2s1 - q2s2
after selection

How many generations will it take to reach equilibrium within 0.02 units ?

What would happen after 5 generations selection if s1 = -0.3 and s2 = -0.5
Would there be any equilibrium ?

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