A gene for reducing horn length of goats in North Cameroon and Chad

Abstract

The histograms of horn length of 2 populations of adult female goats (39 in North Cameroon and 51 in Chad) with a plurimodal shape was analysed and 3 sub-populations were isolated with means of m = 16.00 ± 0.80 cm, m₂ = 10.70 ± 1.70 cm and m₃ = 4.60 ± 0.80 cm for North Cameroon, and m₁ = 21.60 ± 2.60 cm, m₂ = 14.80 ± 1.80 cm and m₃ = 6.00 ± 0.00 cm for Chad. The two populations seemed to carry the same mutation for a reduction of horn length provisionally considered as an autosomal gene with intermediate dominance and with total penetrance. The average effect of substitution of the mutation allele for the wild type allele was 5.80 ± 0.45 cm in North Cameroon and 7.18 ± 0.70 cm in Chad, with a ratio of 0.73, which is very close to that affecting wither height when moving from Chad to North Cameroon (0.75). The mutation was called HR^r (reduced) at the Horn Reduction locus HR, with the wild type allele wild denoted as HR⁺. The gene frequency q was estimated by Maximum Likelihood at the same time as the coefficient of selection, s, of the heterozygote, assuming that the coefficients affecting the homozygotes were zero. By iteration q = 0.44 and s = 2.40. The superiority of heterozygotes over the two homozygotes was thus very strong and the situation approached that of a stable equilibrium where q has a value close to 0.50 provided that the two coefficients of selection of the homzygotes are the same.