The effect of sample size
on the match between
observed and predicted
results of a genetic cross
Joona Kemppainen, ARO
10/15/2009
Contents
1.
2.
3.
4.
Introduction
Method and materials
Results
Appendix
4.1 Chi-Squared tests
1. Introduction
The aim of this practical was to study how the size of sample affects the genotypic and
phenotypic ratios in a genetic cross using a simulation of two Mendelian monohybrid
crosses: Aa x Aa and Aa x aa.
From here on, the cross Aa x Aa will be referred as the first simulation and Aa x aa as the
second simulation.
Predicted genotype ratio from the first simulation is 1:2:1 and phenotype ratio is 3:1.
Predicted genotype ratio and phenotype ratio from the second simulation is 1:1.
2. Method and materials
The simulation was conducted using two dice. Sample sizes of 5, 10, 50, 100 and 150
were used.
3. Results
3.1 The first simulation
Sample size of 5 resulted in genotypes 3 Aa, 1 AA and 1 aa and a phenotype ratio of
4:1.
Sample size of 10 resulted in genotypes 8 Aa, 1 AA and 1 aa and a phenotype ratio of
9:1.
Sample size of 50 resulted in genotypes 28 Aa, 10 AA and 12 aa and a phenotype
ratio of 19:6.
Sample size of 100 resulted in genotypes 50 Aa, 25 AA and 25 aa and a phenotype
ratio of 3:1.
Sample size of 150 resulted in genotypes 78 Aa, 35 AA and 37 aa and a phenotype
ratio of 113:37.
Running Chi-Squared tests on these results gave an average probability that the
differences from predicted values were due to the random factor of 71.56%.
3.2 The second simulation
4. Appendix
4.1 Chi-Squared tests
2nd simulation
1st simulation