Part B-June 2011

CSIR-UGC National Eligibility Test (NET) for Junior Research Fellowship and Lecturer-ship

Previous Solved Questions – 2011 June CSIR-NET Exam

1. Release of nutrients, oxidants or electron donors into the environment to stimulate naturally occurring microorganisms to degrade a contaminant, is referred to as

    1. biostimulation
    2. Phytoremediation
    3. bioaugmentation
    4. bioremediation

Ans:- 1   Expln:-  Biostimulation involves the m bi odification of the environment to stimulate existing bacteria capable of bioremediation. This can be done by addition of various forms of rate limiting nutrients and electron acceptors, such as phosphorus, nitrogen, oxygen or carbon(eg., in the form of molasses).

2. G protein-linked receptors are transmembrane proteins of

  1. single-pass
  2. three-pass
  3. five-pass
  4. seven-pass

Ans:- 4     Expln:- Many transmembrane receptors are composed of two or more protein subunits which operate collectively and may dissociate when ligands bind, fall off, or at another stage of their “activation” cycles. The polypeptide chains of the simplest are predicted to cross the lipid bilayer oly once, while others cross as many as seven times(for example, the so-called G-protein coupled receptors). GPCRs possess 7-transmembrane domain signatures (weaving back and forth across the plasma membrane 7 times) and interact with membrane-associated small G proteins.

3. Small RNAs with internally complementary sequences that form hairpin-like structure, synthesized as precursor RNAs and cleaved by endonucleases to form short duplexes are called

  1. snRNA
  2. mRNA
  3. tRNA
  4. miRNA

Ans:- 4      Expln:- Pre-miRNA hairpins are exported from the nucleus in a process involving the nucleocytoplasmic shuttle Exportin-5. This protein, a member of the karyopherin family, recognizes a two-nucleotide overhang left by the RNase III enzyme Drosha at the 3` end of the pre-miRNA hairpin. Exportin-5-mediated transport to the cytoplasm is energy-dependent, using GTP bound to the Ran protein.

4. A mechanism that can cause a gene to move from one linkage group to another is

  1. crossing over
  2. Inversion
  3. Translocation
  4. Duplication

Ans.  3

5. which of the cyclins have/has essential functions in S-phase of cell cycle ?

  1. A-type
  2. B-type
  3. D-type
  4. Both B-and D-types

Ans:- 1      Expln:-  The passage of a cell through the cell cycle is controlled by proteins in the cytoplasm. Among the main players in animal cells are:

      • Cyclins
        • G1  cyclins (D cyclins)
        • S-phase  cyclins (cyclins E and A)
        • Mitotic  cyclins (B cyclins)

6. The following is the biochemical pathway for purple pigment production in flowers of sweet pea:

 

Colourless  Precursor 1            *           Colourless Precursor 2           *         Purple              pigment
Recessive mutation of either gene A or B leads to the formation of white flowers. A cross is made between two parents with the genotype. AaBb  x  aabb. Considering that the two genes are not linked, the phenotypes of the expected progenies are

 

    1. 9 purple : 7 white
    2. 3 white : 1 purple
    3. 1 purple : 1 white
    4. 9 purple : 6 light purple : 1 white

Ans:-  2         Expln:-  Genes that are similar in phenotypic effect when present separately, but which together interact to produce a different trait are known as complementary genes.
W.Bateson and R.C Punnett, studied the inheritance pattern of flower colour in the sweet pea, Lathyrus odoratus. They found that the wild variety of peas which breeds true are purple flowered . They also noticed that this variety was dominant over the white variety. When two white flowered plants, were crossed, they obtained purple flowered plants in the F1. On selfing the F1, the F2 progeny was obtained in the ratio 9 purple: 7 white.

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The biochemical basis for this pattern of inheritance could be explained as follows: The purple flower colour in sweet pea is due to the pigments called anthocyanins. Production of anthocyanins occurs through a series of metabolic steps catalysed by enzymes. These enzymes are in turn the products of genes. Whenever a step in this synthetic process is blocked by the absence of a functional enzyme, pigmentation does not occur. The genes A and B are both necessary for the production of anthocycanins. If the genotype is either aa or pp, the synthetic pathway is blocked and no pigments are produced resulting in white flowers.

7. In an altruistic act, if a donor sacrifices ‘C’ offspring which helps the recipient to gain ‘B’ offspring and the donor is related to the recipient by a coefficient ?, under which condition would kin selection favour this altruistic trait ?

    1. B>C
    2. B> γ C
    3. γB-C = 0
    4. γB-C>0

 

Ans:- 4       Expln:- Hamilton’s rule –   Kin selection refers to changes in gene frequency across generations that are driven at least in part by interactions between related individuals, and this forms much of the conceptual basis of the theory of social evolution. Indeed, some cases ofevolution by natural selection can only be understood by considering how  biological relatives influence one another’s fitness. Under natural selection, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency within the population;and conversely, a gene that  lowers the individual fitness of its carriers should be eliminated. However, a gene that prompts behavior which enhances the fitness of relatives but lowers that of the individual displaying the behavior, may may nonetheless increase in frequency, because relatives often carry the same gene; this is the fundamental principle behind the theory of kin selection. According to the theory, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behavior. As such, this is a special case of a more general model, called inclusive fitness (in that inclusive fitness refers simply to gene copies in other individuals, without requiring that they be kin.

    1. Formally, such genes should increase in frequency when
      γB>C
      Where
      γ = the genetic relatedness of the recipient to the actor, often defined as the probability that  a    gene picked randomly from each at the same locus is identical by descent.
      B= the additional reproductive benefit gained by the recipient of the altruistic act,
      C= the reproductive cost to the individual of performing the act.

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