151.

In Drosophila, Bar eye (B) is a dominant mutation while miniature wing (m) and yellow body colour (y) are recessive mutations. Heterozygous females for these mutations were crossed to normal eyed miniature winged and yellow body-coloured males. Assume the following progeny was obtained:

Phenotypes	Number
B+m+y+	30
B m y+	25
B m+ y+	165
B+ m y+	120
B m y	20
B+ m y	185
B m+ y	110
B+ m+ y	45

Based on the results obtained, the order of genes will be:

A. B m y

B. m B y

The genetic distance between B and y will be:

C. 40 cM

D. 17.1 cM

The correct combination of answer is

• A and C

• B and C

• A and D

• B and D

A researcher exposed Drosophilalarvae to 37°C during their growth. One of the adult flies that emerged had a crossveinless phenotype. Crossveinless is a known mutant in Drosophila. When this crossveinless fly was crossed to a known crossveinless mutant fly all the progeny had normal phenotype. The observed phenotype can be best explained as an example of

• Conditional mutant

• Phenocopy

• Penetrance

• Pleiotropy

What would be the effect on newt limb regeneration, if more than 90% of the nerve supply is severed before amputation?

• The apical ectodermal cap stimulates growth of the blastema by secreting FGF8 but regeneration does not take place.

• Limb regenration will take place and form a limb with no nerve supply.

• Outgrowth will occur but the identity of the limb formed will be lost with no clear anterior-posterior polarity.

• Limb regeneration with nerve supply will take place.

Following are the events that might take place during dorso-ventral axis specification in early embryonic development of Drosophila:

A. 'Torpedo' receptor activation

B. 'Pipe' synthesis

C. A cascade of protease activity.

D. 'Cactus' dephosphorylation.

E. Entry of 'Dorsal' in the nuclei of syncytial blastoderm stage embryo.

Which combination of the above events will occur in the presumptive dorsal side of the embryo deficient in maternal gurken?

• A only

• B and C only

• B, C, and E only

• B, C, D, and E only

C. elegans embryo uses both autonomous and conditional modes of specification. Conditional specification. Conditional specification at the 4-cell stage can be seen in the development of the endoderm cell lineage and also in the establishment of dorsal-ventral axis. Following are few statements regarding this:

A. If the P₂ cell is removed at the early 4-cell stage, the EMS cell will divide into two MS cells and no endoderm will be made.

B. In pop-1 deficient embryos, both EMS daughter cells become E cells.

C. When the position of ABa and ABp was reversed, their fates get reversed and no normal embryo forms.

D. In embryo whose mother have mutant glp-1, ABp is transformed into ABa cell.

Which of the above statements are true?

• A, B, and D

• A, B, and C

• B, C, and D

• A, C, and D

During vulva development in C.elegans, the anchor cell produces Lin-3 protein which interacts with the Let-23 protein present on the six vulval precursor cells (VPCs) that form an equivalence group. The central lineage cell (P6.p) adopts the primary fate, the adjacent VPCs (P5.p and P7.p) adopt the secondary fate and the rest VPCs adopt the tertiary fate. Few mutants (column A) and phenotypes (Column B) are listed in the table given below.

Match the correct mutant with the observed phenotype.

• A - iv; B - ii; C - iii; D - i

• A - iv; B - iii; C - i; D - ii

• A - ii; B - iii; C - iv; D - i

• A - iii; B - i; C - ii; D - iv

Identification of genes that are associated with the development of male and/ or female gametophyte and embryogenesis in plants is facilitated by T-DNA mediated insertional mutagenesis. In an experiment, a transgenic plant was generated by insertion of T-DNA (containing a Kanamycin-resistance gene) into a gene "A". Self pollination of the T₀ plant generated F₁ progeny that segregated in a 2:1 ratio for resistance : sensitivity to Kanamycin. These observations indicate that

• the mutant allele did not segregate from the wild type allele.

• mutation in gene "A" induces lethality in the male gametophyte.

• mutation in gene "A" induces lethality in the female gametophyte.

• mutation in gene "A" induces zygotic lethality.

Fertilization in sea urchin eggs involves Ca²⁺ release from the endoplasmic reticulum for cortical granule reactivation. The major molecule responsible for releasing Ca²⁺ from intracellular stores is 

• zona pellucida glycoproteins

• protamines 

• inositol 1, 4, 5-trisphosphate

• N-acetylglucosaminidase 

What is observed phenotype when the ultrabithorax gene is deleted in Drosophila?

• The third thoracic segment is transformed into another second thoracic segment resulting in a fly with four wings. 

• Since it specifies the second thoracic segment, instead of antenna leg grows out of the head socket. 

• Since it specifies the third thoracic segment, a fly with two pairs of halters develop. 

• Since this gene fails to be expressed in the second thoracic segment, the antennae sprout in the leg position. 

Which one of the following statements with respect to amphibian development is correct?

• The organizer is itself induced by the Nieuwkoop Centre located in the dorsalmost mesodermal cells.

• The organizer functions by secreting proteins like Noggin, Chordin and Follistatin that blocks BMP signal that would otherwise dorsalize the mesoderm.

• In the presence of BMP activators the ectodermal cells form neural tissue.

• Wnt signalling causes a gradient of b-catenin along the anterior-posterior axis of the neural tube that appears to specify the regionalization of the neural tube.