21.1 – 1 As you learned in chapter 12, mitosis gives rise to two daughter cells that are genetically identical to the parent cell. Yet you, the product of many mitotic divisions, are not just a ball of identical cells. Why?

21.1 – 1 Cells undergo differentiation during embryonic development, becoming different from each other; in the adult organism, there are many highly specialized cell types.

21.1 – 2 What are the fundamental differences between plants and animals in their mechanisms of development?

21.1 – 2 During animal development, movement of cells and tissues is a major mechanism, which is not the case in plants. In plants, growth and morphogenesis continue throughout the life of the plant. This is true only of a few types of animal cells.

21.2 – 1 Why can’t a single embryonic stem cell develop into an embryo?

21.2 – 1 Information deposited by the mother in the egg (cytoplasmic determinants) is required for embryonic development.

21.2 – 2 If you clone a carrot, will all the progeny plants (“clones”) look identical? Why or why not?

21.2 – 2 No, primarily because of the subtle (and not-so-subtle) differences in their environments.

21.2 – 3 The signal molecules released by an embryonic cell can induce changes in a neighboring cell without entering the cell. How?

21.2 – 3 By binding to a receptor on the receiving cell’s surface and triggering a signal transduction pathway that affects gene expression.

21.3 – 1 Why are fruit fly maternal effect genes also called egg-polarity genes?

21.3 – 1 Because their products, made by the mother, determine the head and tail ends, as well as the back and belly, of the egg (and eventually the adult fly).

21.3 – 2 If a researcher removes the anchor cell from a C. elegans embryo, the vulva does not form, even though all the cells that would have made the vulva are present. Explain why.

21.3 – 2 The prospective vulval cells require an inductive signal from the anchor cell before they can differentiate into vulval cells.

21.3 – 3 Explain why cutting and rooting a shoot from a plant, then planting it successfully, provides evidence that plant cells are totipotent.

21.3 – 3 A shoot is a differentiated structure, yet some of the cells that make it up are able to differentiate and redifferentiate, forming all of the organs of the new plant.

21.4 – 1 The DNA sequences called homeoboxes, which help homeotic genes in animals direct development, are common to flies and mice. Given this similarity, explain why these animals are so different.

21.4 – 1 Homeotic genes differ in their nonhomeobox sequences, which determine their interactions with other transcription factors and hence which genes are regulated by the homeotic genes. These interactions differ in the two organisms, as do the expression patterns of the homeobox genes.