Horn Phenotypes and Genotypes in Soay Sheep

(after Appendix 2 in Clutton-Brock & Pemberton, 2004)

Horn development and conformation is controlled by the Ho locus. It appears that there are three alleles which, in various pairings, determine the size and shape of a sheep's horns. The following two tables summarize our current understanding of what these genes do. You'll notice that each gene is written in two alternative typographic conventions: one with superscripts and one without. The first ("Formal") is what is found in printed materials, books and articles. The second ("Simple") is more convenient for use in databases, where the use of superscripts is impractical.

Allele symbol Description
Formal Simple  
Ho+   Ho Wild allele, dominant, horns in both rams and ewes
HoL   hl Sex-limited polling allele, recessive, scurring in ewes, normal horns in rams
HoP  hp Polling allele, recessive to Ho+, dominant to HoL, scurring in rams, polling in ewes.

Genotypes and corresponding phenotypes

Genotype Phenotype
Formal Simple Rams Ewes
Ho+/Ho+ Ho/Ho Horns Horns
Ho+/HoL Ho/hl Horns Horns
Ho+/HoP Ho/hp Horns Scurs
HoL/HoL hl/hl Horns Scurs
HoL/HoP hl/hp Horns Polled
HoP/HoP hp/hp Scurs Polled

Phenotypes and corresponding genotypes

Phenotype Genotypes
Rams Ewes
Horned Ho+/–
Scurred HoP/HoP HoL/HoL
Polled HoP/HoP