In humans, identical twins are possible becausea. 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.

Which of the following is common to the development of both birds and mammals?a. holoblastic cleavageb. epiblast and hypoblastc. trophoblastd. gray crescent

The archenteron develops intoa. 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 membranesb. yolkc. cleavaged. 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.

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 werea. totipotent.b. determined.c. differentiated.d. mesenchymal.

You obtain an egg cell from the ovary of a white mouse and remove the nucleus from it. You then obtain a nucleus from a liver cell from an adult black mouse. You use the methods of nuclear transplantation to insert the nucleus into the empty egg. After some prompting, the new zygote divides into an early embryo, which you then implant into the uterus of a brown mouse. A few weeks later, a baby mouse is born. What color will it be? Why?

In an experiment, a researcher colored a bit of tissue on the ­outside of a frog gastrula with an orange fluorescent dye. The embryo developed normally. When the tadpole was placed under an ultraviolet light, which of the following glowed bright orange? (Explain your answer.) a. the heart b. the pancreas c. the brain d. the stomach

In an embryo, nerve cells grow out from the spinal cord and form connections with the muscles they will eventually control. What mechanisms described in this chapter might explain how these cells 'know' where to go and which cells to connect with?