86 TO 90 QUESTIONS WITH ANSWER OF CSIR UGC NET/JRF EXAMINATION
Q91.For successful fertilization in sea urchin,interaction between the surface of the egg and acrosomal proteins, specifically a 30.5 kDa protein called bindin, is necessary. The following factors could affect this interaction and prevent fertilization-
1.Removal of egg jelly polysaccharides.
2.Removal of bindin receptors on the egg vitelline membrane.
3.Removal of bindin receptors from the egg jelly.
4.Removal of bindin receptors from a single culster on the vitelline membrane.
Which one or the combination above statements is correct?
(A)1 and 4 (B)Only 2
(C)1 and 2 (D)Only 3
Answer-B
Description-Bindin is a 30.5kDa (Head of spermatozoa acrosomal protein) is a major protein of sea urchin required for fertilization(interaction with the surface of egg via specific receptor on egg surface)
Removal of bindin receptors on the egg vitelline memb. will affect this interaction and prevent fertilization.
Q92.A mutant embryo of Drosophila in which one of the major sex determining gene.sex lethal, can only undergo default splicing. was allowed to develop. The following statements are towards explaining the determination of sex of the embryo-
1.The embryo will develop into a male fly.
2.The embryo will develop into a female fly.
3.sex lethal gene product directly regulates sex specific alternate splicing of double sex RNA.
4. sex lethal gene product regulates sex specific splicing of transformer RNA which in turn regulates splicing of double sex RNA.
The correct combination of above statements to explain sex determination of the given embryo is-
(A)1 and 3
(B) 1 and 4
(C)2 and 4
(D) 2 and 3
Answer-B
Description-Sxl-gene is sex lethal gene is a master switch gene for somatic cell determination in D. melanogaster.
In XX animals, Sxl become activated and imposes female development,while in XY animals. Sxl remains inactive and male development ensures.
Therefore,default splicing will inactivate Sxl protein product.Hence male develops.
Also sex lethal is an RNA splicing enzyme whose immediate target is transformer mRNA.Since, Sxl are not transcribed in males, its action on Transformer is restricted to females.
sex lethal acts positively in the functional splicing of transformer mRNA. Transformer is another splicing factor. Hence determines female development fate.
Q93.A two celled embryo made of blastomeres A and B. If the two blastomeres are experientially separated, the A blastomere generates all the cells it would normally make. However the B blastomere in isolation makes only a small fraction of cells it would normally make.Based on the above observations only, which one of the following conclusions is correct?
(A) A blastomere is autonomously specified while B blastomere is conditionally specified.
(B) A blastomere is conditionally specified while B blastomere is autonomously specified.
(C) Descendants of A blastomere are autonomously specified.
(D)Descendants of B blastomere can either be autonomously specified or conditionally specified.
ANSWER-A
94.A mutant was experimentally generated which has wings reduced to haltere like structure. The following statements are put forward regarding this phenotype-
1.ultrabithorex gene ectopically expressed in second thoracic segment.
2. antennapedia gene ectopically expressed in second thoracic segment.
3.A homeotic mutation.
4. A mutation in gap gene.
The following combination of statements will be most appropriate explaining the molecular basis of mutant phenotype-
(A)1 and 2
(B)2 and 3
(C)3 and 4
(D)1 and 3
ANSWER-D
Description- Ultrabithorax (activated in absence of hunchback protein) Ubx gene found in insects.
In D.melanogaster it is expressed in the 3rd thoracic and 1st abdominal segments and repress wing formation. Ubx gene regulates the decisions regarding the no. of wings and legs.
Homeotic mutation causes tissues to alter their normal differentiation pattern producing integrated structures but in unusual locations.
Q95.Following are certain statements regarding the activities of homeotic genes of classes A,B and C involved in floral organ identity-
1.Activity of A alone specifies sepals.
2.Activity of B alone specifies petals.
3.Activity of B and C form stamens.
4.Activity of C alone specifies carpels.
Which one of the following combinations of above statements is correct?
(A)1,2 and 3
(B)1,2 and 4
(C)2,3 and 4
(D)1,3 and 4
ANSWER-D
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