20. Development

What is apoptosis? a. an experimental technique used to kill specific cells b. programmed cell death that is required for normal development c. a pathological condition observed only in damaged or diseased organisms d. a developmental mechanism unique to the roundworm C. elegans

In adult animals,          are a source of undifferentiated cells that can divide to produce cells that can specialize.

What does it mean to say that a characteristic is heritable? a. The characteristic evolves. b. The characteristic can be passed on to offspring. c. The characteristic is advantageous to the organism. d. The characteristic does not vary in the population.

Could both the food competition hypothesis and the sexual competition hypothesis explain why giraffes have long necks? Why or why not?

Cell differentiation always involves a. transcription of the myoD gene. b. the movement of cells. c. the production of tissue-specific proteins. d. the selective loss of certain genes from the genome.

A friend is interested in isolating genes that are expressed solely in liver cells but only has access to skin cells. She asks you for advice on whether to start her studies. What will you say?

What did Linnaeus' system of naming organisms ensure? a. Two different organisms never end up with the same genus and species name. b. Two different organisms have the same genus and species name if they are closely related. c. The genus name is different for closely related species. d. The species name is the same for each organism in a genus.

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of a. the influence of environment on development. b. paedomorphosis. c. a change in a developmental gene or in its regulation that altered the spatial organization of body parts. d. heterochrony.

Your bone cells, muscle cells, and skin cells look different because a. each cell contains different kinds of genes. b. they are present in different organs. c. different genes are active in each kind of cell. d. they contain different numbers of genes.

The following predictions ask you to consider how genetic regulatory cascades provide positional information. Select True or False for each statement. T/F Mutation of a gene at one level of a regulatory cascade will affect the expression of genes at all levels of the cascade. T/F Mutation of a gene that is expressed later in a regulatory cascade will affect a smaller region of the body than mutation of gene that is expressed early in the cascade. T/F In the regulatory cascade used by Drosophila, a gene at one level of the cascade will be controlled only by genes at the level immediately above it. T/F Genes that control the largest regions of the Drosophila embryo are not transcribed in the embryo.

Locate fluorine (F) on the partial periodic table provided in Figure 2.2. Predict its relative electronegativity compared to hydrogen, sodium, and oxygen. State the number and type of bond(s) you expect it would form if it reacted with sodium (Na).

Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior larval body parts and mirror-image duplication of posterior parts. This is evidence that the product of the bicoid gene a. normally leads to formation of head structures. b. normally leads to formation of tail structures. c. is transcribed in the early embryo. d. is a protein present in all head structures.

What is the connection between genetic regulatory cascades and the observation that differentiation is a step-by-step process?

What is 'selected' during natural selection? Explain your answer.

Which of the following provides the strongest evidence for the conservation of tool-kit genes? a. Bicoid moved from one fly embryo into the posterior of another fly embryo causes the formation of two head regions. b. Mutation of an unrelated gene in another species of fly has a similar effect to mutation of bicoid in Drosophila. c. A mouse Hox gene can be used to take over the function of a mutated Drosophila Hox gene. d. Sheep can be cloned by fusing a differentiated adult cell with an enucleated egg.

DRAW IT 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.

PROCESS OF SCIENCE Explain why researchers formulate a null hypothesis in addition to a hypothesis when designing an experimental study.

Imagine a situation in which a morphogen has its source at the posterior end of a Drosophila embryo. Every 100 µm from the posterior pole, the morphogen concentration decreases by half. If a cell required 1/16th the amount of morphogen found at the posterior pole to form part of a leg, how far from the posterior pole would the leg form? a. 100 μm b. 160 μm c. 400 μm d. 1600 μm

Some stickleback fish develop protective spines, and other stickleback fish are spineless. Spine development is controlled by the expression of a gene known as Pitx1. The spineless phenotype is due to a mutation in Pitx1 that results in no expression of Pitx1 during development in regions where spines would otherwise form. When scientists compared the Pitx1 coding sequence in spined and spineless fish, they found this sequence was the same in both types of fish. Propose plausible hypotheses for the location of this mutation and for how it alters spine development.

Some humans have genes that make them resistant to infection by HIV. Would human populations likely evolve differently in areas of the world where HIV infection rates are high? Explain your logic.

Type I diabetes is a form of diabetes that is due to the loss of insulin-producing cells of the pancreas. The potential of stem cells—in particular, induced pluripotent stem (iPS) cells—for therapy has gotten a lot of press. What are iPS cells? a. cells taken from early human embryos b. cells taken from the pancreas of people without diabetes c. cells derived by de-differentiating specialized adult cells d. cells derived by differentiating pancreas precursor cells

Type I diabetes is a form of diabetes that is due to the loss of insulin-producing cells of the pancreas. The potential of stem cells—in particular, induced pluripotent stem (iPS) cells—for therapy has gotten a lot of press. If researchers were attempting to stimulate the differentiation of iPS cells, which of the following would they most likely add to the cell-culture medium (the liquid surrounding the cells)? a. activin A, an extracellular signal protein b. Sox-2, a transcription factor active in early development c. Grb-2, an intracellular signal transduction protein d. lactase, an enzyme that catalyzes the breakdown of lactose