Nuclear inheritance in paramecium (Kappa particles (K))

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 Kappa particles in Paramecium  

Sonneborn  found two types of strain in paramecium .i. e. Killer and sensitive. 
  • Killer strain : Killer strains contain Kappa particles * .These strains produce a poisonous substance called paramecin with the help of kappa particles.  These kappa particles remain unaffected in presence of paramecin. 
*kappa particles : these are self duplicating cytoplasmic particles found in Paramecium aurelia . These particles make the animal killer when present in sufficient number. 
The kappa particles can be retained one in those individuals which possess a dominant gene K (having recessive allele K) in nucleus. 

Cross between killer and sensitive strain 

  • Conjugation takes place for less time : when conjugation takes place for less than three minutes, only nuclear exchange takes place. Formation of cytoplasmic bridge doesn't takes place. After conjugation each race produces its own type. 

  • Conjugation takes place for longer time : When conjugation takes place for longer time, cytoplasmic bridges May be formed. In this case, a portion of cytoplasm is also exchanged. After this type of conjugation both the ex-conjugats produce killers. 

Conclusion : 

Due to nuclear exchange in both the Cases sensitive conjugation receive dominant K from killer strain. 
  • In first case, because there is no cytoplasmic exchange only killer ex-conjugats produce killer and sensitive offsprings. While sensitive strain also with same genotype Kk produces only sensitive as its cytoplasm lacks kappa particles. 
  • In second case, because sensitive strain receive kappa particles due to cytoplamic exchange, it is also able to produce killer KK as well as sensitive kk offsprings.


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