Cytoplasmic Inheritance: Extrachromosomal Inheritance

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Extrachromosomal Inheritance:
n.
Inheritance of traits through DNA that is not connected with the chromosomes but rather to DNA from organelles in the cell. Also called cytoplasmic inheritance. Essay on “Cytoplasmic Inheritance”
Inheritance of characters from parents to offspring is primarily dependant on the nucleus. Oscar, Her twig etc., had established in 1870 itself the importance of nucleus in the hereditary transmission of characters. The discoveries of Mendel further provided the genetic evidence for nucleus being the seat of all hereditary characters. The nucleus forms specific number of chromosomes during cell division and these duplicate, maintaining their number in future cell generations. Chromosomal aberrations, both structural and numerical leading to phenotypic abnormalities provided further proof for chromosomes albeit nucleus to be the only organelle concerned with the transmission of characters. The discovery of sex linked characters gave further impetus for the chromosome theory of inheritance as it was firmly established that a particular trait followed a particular chromosome. An additional proof for chromosomes being the only link between one generation and the other is the fact the gametes, at least the male gamete consists of mainly the nucleus and very little amount of cytoplasm. With all these overwhelming evidences in favor of nuclear inheritance it was but natural for geneticists to believe that nucleus is the only seat where all the genetic potentialities are located But there are several instances of a peculiar type of transmission of characters both in the animal and plant kingdom which seemed to defy every known genetic law assuming the whole of inheritance to be through the nucleus. The inheritance of flower color in 4° Clock plants, Kappa particles in Paramecium etc, cannot be explained on the basis of nuclear inheritance. What then is the secret of their inheritance pattern? Scientists started looking for other...
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