Table 20-2: The Fitness Advantage of Sickle-Cell Heterozygotes

 Genotype

Observed phenotype frequency

Expected phenotype frequency

Ratio of observed/expected

W (relative fitness)

Selective advantage

SS

      29

  187.4

0.155

0.155/1.12 = 0.14

AS

  2993

2672.4

1.12  

  1.12/1.12 = 1.00

1.0/0.88 = 1.136

AA

  9365

9527.2

0.983

0.983/1.12 = 0.88

Total

12,387

12,387