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Question

Extranuclear inheritance occurs in

A
Killer Paramecium
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B
Killer Amoeba
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C
Euglena
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D
Hydra
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Solution

The correct option is A Killer Paramecium
Extranuclear inheritance or cytoplasmic inheritance is the transmission of genes that occur outside the nucleus. It is found in most eukaryotes and is commonly known to occur in cytoplasmic organelles such as mitochondria and chloroplasts or from cellular parasites like viruses or bacteria.
In Paramecium, small granular particles are present in the cytoplasm called as kappa particles. Kappa particles produce a protein called paramecin that kills the sensitive strain without kappa particles. The strain with the kappa particles is called as killer/resistant strain and the other strain is called as sensitive strain. Gene responsible for producing kappa particles is present in homozygous or heterozygous dominant condition in killer strain while it is present in recessive form in sensitive strain. Paramecium reproduces both by sexual and asexual mode. During asexual reproduction, when conditions favour the cells undergo cell division while the kappa particles cannot divide at the same rate. Therefore, the daughter cells receive less number of kappa particles and after few generations there can be complete loss of kappa particles. In this situation, strains with dominant alleles remain without any kappa particles. This proves the gene for kappa particles can only help in multiplication of existing kappa particles. During sexual reproduction, when two opposite strains conjugate, the killer strain and the sensitive strain remain as the period of conjugation is less. When conjugation period increases, the kappa particles move from killer strain to sensitive strain through conjugation tube converting sensitive strain to killer strain.

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