Animal Development

How does the use of particular labeled nucleosides allow independent measurement of DNA and RNA synthesis?

Describe the changes in synthesis that occur at the end of cleavage (time point 5 corresponds to cell division 12).

Comparing the rate of DNA synthesis with and without cytochalasin B, the researchers hypothesized that the toxin increases the diffusion of thymidine into the embryos. Explain their logic.

Do the data support the hypothesis that the timing of the end of cleavage depends on counting cell divisions? Explain.

In a separate experiment, researchers disrupted the block to polyspermy, generating embryos with 7 to 10 sperm nuclei. At the end of cleavage, these embryos had the same nucleus- to-cytoplasm ratio as the wild-type embryos, but cleavage ended at the 10th cell division rather than the 12th cell division. What do these results indicate about the timing of the end of cleavage?

How does the fertilization envelope form in sea urchins?

What is its function?

Predict what would happen if Ca²⁺ was injected into an unfertilized sea urchin egg.

Review Figure 12.16 on cell cycle control. Would you expect MPF (maturation-promoting factor) activity to remain steady during cleavage? Explain.

In the frog embryo, convergent extension elongates the notochord. Explain how the words convergent and extension apply to this process.

WHAT IF? Predict what would happen if, just before neural tube formation, you treated frog embryos with a drug that enters all the cells of the embryo and blocks the function of microfilaments.

MAKE CONNECTIONS Unlike some other types of birth defects, neural tube defects are largely preventable. Explain (see Figure 41.4).

How do axis formation and pattern formation differ?

How does a morphogen gradient differ from cytoplasmic determinants and inductive interactions with regard to the set of cells it affects (see Concept 18.4)?

WHAT IF? If the ventral cells of an early frog gastrula were experimentally induced to express large amounts of a protein that inhibits BMP-4, could a second embryo develop? Explain.

WHAT IF? If you removed the ZPA from a limb bud and then placed a bead soaked in Sonic hedgehog in the middle of the bud, what would be the most likely result?

The cortical reaction of sea urchin eggs functions directly in

(A) the formation of a fertilization envelope.

(B) the production of a fast block to polyspermy.

(C) the generation of an electrical impulse bythe egg.

(D) the fusion of egg and sperm nuclei.

Which of the following is common to the development of bothbirds and mammals?

(A) holoblastic cleavage

(B) epiblast and hypoblast

(C) trophoblast

(D) gray crescent 

The archenteron develops into

(A) the mesoderm.

(B) the endoderm.

(C) the placenta.

(D) the lumen of the digestive tract.

What structural adaptation in chickens allows them to lay their eggs in arid environments rather than in water?

(A) extraembryonic membranes

(B) yolk

(C) cleavage

(D) gastrulation

If an egg cell were treated with EDTA, a chemical that binds calcium and magnesium ions,

(A) the acrosomal reaction would be blocked.

(B) the fusion of sperm and egg nuclei would be blocked.

(C) the fast block to polyspermy would not occur.

(D) the fertilization envelope would not form.

In humans, identical twins are possible because

(A) extraembryonic cells interact with the zygote nucleus.

(B) convergent extension occurs.

(C) early blastomeres can form a complete embryo if isolated.

(D) the gray crescent divides the dorsal-ventral axis into new cells.

Cells transplanted from the neural tube of a frog embryo to the ventral part of another embryo develop into nervous system tissues. This result indicates that the transplanted cells were

(A) totipotent.

(B) determined.

(C) differentiated.

(D) mesenchymal.

Each blue circle in the figure below represents a cell in a cell lineage. Draw two modified versions of the cell lineage so that each version produces three cells. Use apoptosis in one of the versions, marking any dead cells with an X.

Evolution in insects and vertebrates has involved the repeated duplication of body segments, followed by fusion of some segments and specialization of their structure and function. In vertebrates, what anatomical features reflect segmentation?

Scientists can now make identical copies, or clones, of animals ranging from dairy cows to pet cats. Propose a few arguments for and against this application of discoveries about embryonic development.

In a short essay (100–150 words), describe how the emergent properties of the cells of the gastrula direct embryonic development.

Occasionally, two-headed animals such as this turtle are born. Thinking about the occurrence of identical twins and the property of totipotency, explain how this might happen.