Supergenes in polymorphic land snails. II. Partula suturalis.

The colour and banding of the shell of Partula suturalis are controlled by a single locus (M) with a series of at least six alleles. MX, giving apex as a homozygote, is dominant to MF1, giving frenata, which is dominant to the other alleles. MF2 is similar to MF1 except in its relation with MA. MF2MA produces bisecta and provides a striking example of a heterozygote that is qualitatively different from both homozygotes for the alleles producing it. MA gives atra as a homozygote and is dominant to MC and MS. MC, giving cestata as a homozygote, is recessive to all except MS. MS, giving strigata, is the universal recessive. It is suggested that the locus may be complex. The direction of coiling of the shell is determined by the H locus with HS (sinistrality) dominant to HD (dextrality). The expression of coiling is delayed by one generation, the maternal genotype determining the phenotype of the offspring. M and H are not linked. Self-fertilisation occurs infrequently and non-randomly.