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  • Cytoplasmic Inheritance – Zoology Notes – For W.B.C.S. Examination.
    Posted on January 4th, 2020 in Zoology
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    Cytoplasmic Inheritance – Zoology Notes – For W.B.C.S. Examination.

    W.B.C.S. Exam is conducted by PSC, WB in three stages- Prelims, Mains and Interview. The marks you fetch in W.B.C.S. Mains Exam decide your ranking in the final list. The WBCS Mains exam has 8 papers, including twp optional papers. Zoology is an optional subject for Civil Services Mains examination. Zoology requires a huge amount of hard work. This optional paper is also quite lengthy. Aspirants should be thorough with the syllabus. Knowing the syllabus will help you to understand what to study what not to study.The clearest example of cytoplasmic inheritance in animal cells is the mitochondrial genome. The approximately 16,000 base-pair circular mitochondrial genome has genes for ribosomal RNAs, transfer RNAs, and approximately a dozen mitochondrial proteins, including a polymerase (Cummins, 1998).Continue Reading Cytoplasmic Inheritance – Zoology Notes – For W.B.C.S. Examination.

    Although the vast majority of mitochondrial proteins are specified by chromosomal genes, the mitochondrial genome has considerable variability, and mutates more readily than chromosomal genes, in part due to poor proofreading during DNA synthesis (Cummins, 1998). The resulting mutations are the source of considerable (cytoplasmic) genetic disease, as well as phenotypic variation in normal mitochondrial function. Although there are rare exceptions (Cummins, 1998), for the most part mitochondrial genomes are inherited via the maternal ooplasm. The relatively few mitochondria introduced by the sperm usually degenerate, and in any case become so dilute that they usually would not end up in the relatively few cells of the blastocyst that differentiate into the resulting animal.

    The maternal lineages of mitochondria in the recipient oocyte and in the donor nucleus often will be different. Simply by the process of dilution, the animal resulting from cloning procedures using cell fusion usually ends up with mitochondrial genes of the oocyte, not the donor nucleus. Of course, mitochondria will be heteroplasmic initially; sometimes this situation persists, and rarely the donor mitochondria out-compete the recipient oocyte mitochondria, but usually the mitochondria of the recipient oocyte prevail (Evans et al., 1999). It is also possible that donor mitochondria do not survive well in ooplasm because of the very specially differentiated state of mitochondria in oocytes (Cummins, 1998). Experiments to sort this out are progressing, and it is obvious that answers will have a statistical quality rather than a simple outcome. Note that, in the future, it is likely that heteroplasmy of mitochondrial genomes can be eliminated by selective elimination of donor or recipient mitochondria by chemical or other means.Click here to find the Syllabus for Zoology in WBCS Exam.

    The zygote, arisen by uniting of a “green” and a “white” sexual cell, contains two different plastids, green and white ones. In the course of cell divisions forming the embryo, the plastids segregate to the daughter cells according to the laws of probability. If a daughter cell has only white plastids, all the cells derived from it will be white generating a white patch of cells. If the cell has only green plastids, a green complex of cells is produced. There is no need for me to further analyze (the point) that cells with both kinds of plastids will be able to continue to segregate.

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