1. A study of primary wing feather development rate in guinea fowl revealed genetic control through a single pair of sex-linked alleles. The allele for slow feathering (K) was dominant over that for rapid feathering (k+). 2. Wing feather sexing showed 94% accuracy in 10-d-old keets. 3. Incidence of rapid feathering allele (k+) was higher in the population selected for high body weight compared to the unselected population.