Imagine you are studying neural tissue specification in the Xenopus model. The dorsal (“top”) part of the Xenopus blastula, called the “animal cap”, normally forms ectoderm-derived neural tissue and epidermis.

When the animal cap is cut away from the rest of the blastula and grown by itself in culture, it only forms epidermis. This suggests some sort of secreted factor is required for induction of neural tissue. You add a growth factor protein called Noggin to the cultured animal cap and carry out staining for a marker of neural tissue. This is the result, where positive staining is dark:

What conclusion can be drawn? Choose the CORRECT answer.

A researcher interested in neural crest cell migration grafts a small segment of anterior neural tube from a quail embryo into the neural tube of a chicken embryo.

As a control, the researcher places quail anterior neural tube cells back into recipient quail embryos. After 2 days, the researcher finds that the quail cells have failed to migrate in the chicken embryo, but they migrate in quail to populate areas of the face. What can the researcher conclude?

Choose the best answer.

Which of the following is a potential disadvantage of using Xenopus as an experimental model for human development? Choose the CORRECT answer

The figure below shows two types of viable cells derived from a parent cell after cell division (cell A and cell B). Cell B then expresses transcription factor 1 (in green) but not cell A.

Why might cell B express the transcription factor, but not cell A? Choose the CORRECT answer.

Consider the figure below.

What type of molecule is denoted by the black arrow? Choose the CORRECT answer