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: 3811

#Unit 3. Fundamental Processes

The mechanism of DNA replication is studied in an E. coli replication fork. Which is a characteristic of this replication fork?

#Question id: 3812

#Unit 3. Fundamental Processes

The mechanism of DNA replication is studied in an E. coli replication fork. Which is a characteristic of this replication fork?

#Question id: 3813

#Unit 3. Fundamental Processes

The mechanism of DNA replication is studied in an E. coli replication fork. Which is a property of Okazaki pieces in an E. coli replication fork?

#Question id: 3814

#Unit 3. Fundamental Processes

The mechanism of DNA replication is studied in an E. coli replication fork.

Which is a property of RNA primers in an E. coli replication fork?

#Question id: 3815

#Unit 3. Fundamental Processes

Use the figure to answer the following question. A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in the figure would you expect if the DNA was replicated in a conservative manner?

#Question id: 3816

#Unit 3. Fundamental Processes

The mechanism of DNA replication is studied in an E. coli replication fork. Which is a characteristic of an E. coli replication fork and a eukaryotic replication fork?