A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?

#Question id: 7238

#Unit 5. Developmental Biology

Following are the statements regarding to establishment of positive feedback loops for limb bud formation.

A. In the presumptive forelimb field, Tbx5 induces Wnt2b, which then upregulates Fgf10, which in turn positively feeds back to maintain activation of both Wnt2b and Tbx5.

B. Mesodermal Fgf10 tells the surface ectoderm to continue to make Fgf8, and the surface ectoderm continues to tell the underlying mesoderm to make Fgf10.

C. Fgf10 provides the signal to initiate and propagate the limb-forming interactions between ectoderm and mesoderm, and these signaling interactions directly promote limb bud formation and growth.

D. The Wnt protein acts through the canonical β-catenin pathway to induce Fgf8 expression in the ectoderm. This relay of signaling represents a foundational stage in the formation of limb buds, because once Fgf8 is made in the surface ectoderm, the surface ectoderm elongates to physically become the AER.

Which of the following statements correctly explained positive feedback loops during limb development?

#Question id: 7239

#Unit 5. Developmental Biology

C. elegans embryo uses both autonomous and conditional modes of 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 figure:

A. If the P2 cell is removed at the early 4-cell stage, the EMS cell will divide into two MS cells and endoderm will be made.

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

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

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

Which of the above statements are true?

#Question id: 7240

#Unit 5. Developmental Biology

Given below are the list of some organism (column A) and determination of their dorsal-ventral axis (column B)

 Choose the correct option:

#Question id: 7241

#Unit 5. Developmental Biology

If planaria are irradiated at a dosage that destroys nearly all neoblasts. Transplanting a single clonogenic neoblast in this planaria results:

#Question id: 7242

#Unit 5. Developmental Biology

The cells of  posterior marginal zone act as the equivalent of the amphibian Nieuwkoop center because:

A. once the PMZ has formed, it controls the other regions of the margin.

B. Cells of PMZ initiate other regions of the margin from forming their own primitive streaks.

C. the entire marginal zone produces Wnt8c (capable of inducing the accumulation of -catenin) and secrete Vg1, a member of the TGF-family.

D. The PMZ cells secretes nodal protein and Nodal activity is needed to initiate the primitive streak.

E. When placed in the anterior region of the marginal zone, a graft of PMZ tissue (posterior to and including Koller’s sickle) is able to induce wnt signaling.

Which of the following option is correct?

#Question id: 7243

#Unit 5. Developmental Biology

Match the following: