Chapter 92 Differences in Fitness

What the simulation does

Open file 92-GenePoolChanges.xlsx. This simulation is similar to the previous simulation, but this time we also assign relative fitness factors—for instance, genotype AS (cell U4: 1) is more “fit” than genotype SS (cell U2: 0.4). So gradually, up to a certain point, the frequency of AS will increase, while the frequency of genotype SS (sickle cell anemia, for instance) will decrease in later generations.

What you need to know

All the gray cells on the sheet have formulas in it. We assume that parents have up to 4 children each generation (columns F:I). Most formulas are identical to the ones used in Simulation 91.

The main difference is that the range X2:AA10 is based on the different fitness factors for each genotype. The offspring is not only determined by Mendel’s laws but also by the fitness of that specific genotype. That’s why certain cells remain empty.

This will obviously affect frequencies in the next generation. Key is the range O34:Q34, which shows the average frequencies based on 50 couples with up to 4 children after 20 runs. We will also see the effect after two more generations on the 2nd and 3rd sheet.

What you need to do

  1. Offspring varies, so place in range X2:AA10: =IF(RAND()<VLOOKUP(O2,$T$2:$U$4,2,0),O2,””).
  2. Place in the entire range F11:I60 this formula: =IF(RANDBETWEEN(0,6)>COLUMN(A1),VLOOKUP($B11&$C11,$W$2:$AA$10,RANDBETWEEN(2,5),FALSE),””).
  3. All the other formulas are the same as the ones used in Simulation 91.
  4. On the 2nd sheet, for the second generation, we changed range D2:D4 by replacing it with links to the frequencies after 1 generation on the 1st sheet in range O34:Q34.
  5. On the 3rd sheet, for the third generation (see below), we changed range D2:D4 again, but now by replacing it with links to the frequencies after 2 generations in range O34:Q34 on the 2nd sheet.
  6. You will probably find that the SS frequency has declined—in this particular case, from 10% to 3%, and then back to 4%.