Question

Cytoplasmic inheritance and extracellular inheritance by biology discussion

Answer 1

Answer -

• ADVERTISEMENTS: The genes controlling cytoplasmic inheritance are present outside the nucleus and, in the cytoplasm, they are known as plasma genes, cytoplasmic genes, cytogeneses, extra nuclear genes or extra chromosomal genes. The sum total of the genes present in cytoplasm of a cell is known as Plasmon

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Answer 2

Cytoplasmic Inheritance:

The existence of genes as segments of nu­cleic acid molecules, located in chromosome of nucleus, has been demonstrated by several experiments. The nuclear genes control the phenotypes of the organisms and are concerned with the transmission of hereditary charac­ter from one generation to next generation is known and predictable Mendelian fashion.

The inheritance of genes of nuclear chromosomes is characterised by the fact that the genes from male and female parents contribute equally to the genetic constitution of the offspring. There­fore, in it the reciprocal crosses between parents of different homozygous genotype will produce offspring’s of identical phenotypes except for sex-linked genes.

Explanation:

and female parents contribute equally their nuclear genes to the offspring’s, the results show a non-Mendelian inheritance pattern and the result of reciprocal crosses varies.

These variations suggest that the genes for the inheritance of certain characters do not occur within the nucleus, but they are present ill cytoplasm and play an important role in transmission of certain specific traits, which are not controlled by nuclear genes. Therefore, it builds up the concept of cytoplasmic inheri­tance. The genes for cytoplasmic inheritance are independent, self-replicating nucleic acids.

Evidence for cytoplasmic inheritance was first reported by Correns in Mirabilis jalapa and by Bar in Pelargonium zonule in 1908. Rhoades described cytoplasmic male sterility in maize in 1933. In 1943, Sonneborn discovered kappa particles in Paramoecium and described its cytoplasmic inheritance. Presence of DNA in chloroplasts was first demonstrated by Ris in plant cell.

In 1963, Nass and his co-workers proved the existence of DNA in mitochondria. Subsequently, from time to time, observations by several scientists have been reported the im­portant role of cytoplasm in genetics. Thus, on the basis of observations made on cytoplasmic inheritance of some specific traits, it has been suggested that cytoplasm is also genetically active.Extra-chromosomal inheritance, extra-nuclear inheritance, somal inheritance and maternal inheritance are all synonyms. All these terms can be defined as the inheritance of characteristics of only one of the two parents, usually the female parent to the progeny. The reciprocal crosses show consistent differences as well as there is a lack of segregation in F2 and subsequent generations.