Kappa particles in Paramecium

Cytoplasmic Inheritance Involving Dispensable Hereditary Units (nuclear genes may or may not be involved)
Kappa particles in Paramecium
Kappa particles are found in certain killer strains of Paramecium and are responsible for production of substance paramecin, which is toxic to strains not possessing kappa (sensitive strain). The production of kappa particles is dependent on a dominant allele K, so that killer strains are KK or Kk and sensitive strains are ordinarily kk. In absence of dominant allele K, kappa particles cannot multiply and in absence of kappa particles, dominant allele K cannot produce them de novo. Consequently sensitive strains with genotypes KK or kk can be obtained. These will not carry any kappa particles. However, killer strain with genotype kk cannot be obtained, because even if kappa particles are present, these would be lost in absence of dominant allele. If Paramecium clones with genotypes KK or Kk are allowed to multiply asexually at such a fast rate, that division of kappa particles cannot keep pace with division of cells, kappa particles will be eventually lost. Consequently sensitive strains with dominant genotype (KK, Kk)having no kappa particles would be obtained.

If the killer (KK)and sensitive (kk)strains are allowed to conjugate, all exconjugants (the cells separating after conjugation) will have same genotype Kk. Phenotypes of these exconjugants will, however, depend upon duration for which conjugation is allowed. If conjugation does not persist long enough for exchange of cytoplasm, heterozygote (Kk)exconjugants will only have parental phenotypes. It means that killers will remain killers and sensitive will remain sensitive even after conjugation (Fig. 18.5). If conjugation persists, sensitive strain will receive kappa particles and will become killer, so that exconjugants will be killers having genotype Kk (Fig. 18.6).