Question 5

The folding of sheets of cells, the migration of cells, and cell death are all mechanisms of:

a) cleavage division.

b) pattern formation.

c) morphogenesis.

d) differentiation.

e) growth.Question 7

The establishment of the anterior-posterior or dorsal-ventral body axes is called:

a) division.

b) pattern formation.

c) morphogenesis.

d) differentiation.

e) growth.Question 8

The pathway from a gene to a protein in eukaryotic cells involves:

a) first, transport of mRNA, then its processing, then transcription, then translation.

b) first, transcription of the RNA, then its transport, then processing, then translation.

c) first, translation of the RNA, then its transport, then its processing, then transcription.

d) first, transcription of RNA, then its processing, then its transport, then translation.

e) first, processing of the RNA, then its transport, then transcription, then translation.

Question 9

Which of the following is not a mechanism by which cells communicate with each other?

a) Transcription factors are secreted from one cell and taken up by the target cell, where they influence gene expression.

b) Cell surface molecules on adjacent cells interact and initiate a signal transduction process that influences cellular behavior and gene expression.

c) Cells form gap junctions with adjacent cells, allowing the passage of small molecules.

d) Cells secrete proteins and small hydrophilic molecules, which interact with cell surface receptors on target cells and initiate a signal transduction process that influences cellular behavior and gene expression.

e) Cells secrete small hydrophobic molecules which diffuse into target cells, interact with cytoplasmic receptors, and influence gene expression.

Question 10

Signal transduction can involve:

a) interaction of a molecule with a receptor at the cell surface.

b) intracellular modification of proteins by phosphorylation.

c) production of second messengers such as cAMP.

d) all of the above can be components of a signal transduction pathway.

e) none of the above are components of signal transduction pathways.

This chapter discusses the embryonic development of Drosophila melanogaster. How long does embryonic development take in this organism?

a) One hour.

b) Three hours.

c) One day.

d) Ten days.

e) Nine months.Question 2

The portion of the blastoderm-stage embryo which will give rise to most ectodermal, mesodermal, and endodermal tissues is called the:

a) ventral.

b) germ band.

c) imaginal discs.

d) amnioserosa.

e) germ line.Question 3

The development of the antero-posterior axis of Drosophila is initiated when:

a) the mother packages bicoid and nanos mRNA into the developing oocyte.

b) the Toll receptor is activated after fertilization, leading to nuclear localization of Dorsal protein.

c) the terminal group protein Torso sets up the anterior and posterior poles of the embryo.

d) the homeotic genes specify the fate of individual segments.

e) the sperm enters the micropile at the anterior end, thus specifying the antero-posterior axis.

Question 4

Which would lead to a dorsalized embryo? (Recall that genes in Drosophila are named for their mutant phenotype.)

a) Dorsal mutant.

b) Cactus mutant.

c) Toll mutant.

d) Spätzle mutant.

e) Bicoid mutant.Question 5

A gap gene mutation might cause which of the following defects in the embryonic body plan?

a) Every other segment would be missing, resulting in T1, T3, A2, A4, etc. but no T2, A1, A3, and so on.

b) Segments A2 through A6 would be missing, but the rest of the pattern is essentially normal.

c) No segmentation would be evident.

d) Patterning within each segment would be abnormal, causing for example denticle belts to form across the entire segment.

e) The identity of one or more segments would be transformed to that of a different segment, such that the T3 leg would transformed to a T2 leg.

Question 6

The activation of zygotic hunchback expression by Bicoid protein illustrates what principle in the establishment of positional information in embryos?

a) The mother can influence development through the packaging of materials into the egg.

b) A gradient of a protein can activate a gene in a discrete region of an embryo through a threshold effect.

c) The identity of segments in the embryo is a reflection of their position in the embryo.

d) A cascade of gene activations occurs in the syncitial blastoderm.

e) Genes are activated or repressed by the binding of transcription factors to their regulatory regions.

Question 7

The portion of the Drosophila body plan which will produce the wing is called:

a) telson.

b) dorsal.

c) abdomen.

d) thorax.

e) neurectoderm.Question 8

The adult body plan of the fly is based on reiterating structures called segments; segment precursors (parasegments) are first positioned at the cell-by-cell level by which group of genes?

a) Maternal genes such as bicoid.

b) Gap genes such as Kruppel.

c) Pair-rule genes such as even-skipped.

d) Segmentation genes such as engrailed.

e) Homeotic genes such as antennapedi.Question 9

Mutations in homeotic genes can lead to what type of developmental defect?

a) The anterior portion of the embryo does not develop.

b) Several adjacent segments will be missing from an otherwise intact embryo.

c) The embryo will develop with every other segment failing to form.

d) Segment and compartment boundaries will fail to form.

e) The development of segments will be changed wholesale from their normal identity to that of a different segment.

Question 10

Which of the following, first discovered through mutagenesis studies in Drosophila, also function in the development of mammals like ourselves?

a) Hedgehog.

b) Homeobox genes.

c) The Wnt family.

d) The Toll signalling pathway.

e) All of the above. FROG

on 1

In which portion of the frog's life-cycle would a frog appear most similar to a mammal?

a) The fertilized eggs of frogs and mammals are similar in size and look nearly identical.

b) A frog blastula is very similar to a mammalian blastocyst.

c) The events of gastrulation in frogs are highly similar to gastrulation and extraembryonic membrane formation in mammals.

d) Late in organogenesis, at the phylotypic stage, the body plans of frogs and mammals are remarkably similar.

e) Adult frogs are essentially indistinguishable from adult humans.Question 2

The notochord is a ___ structure in vertebrate embryos that lies under the ___, and is flanked by ___.

a) mesodermal, neural tube, somites

b) endodermal, mesoderm, the gut

c) ectodermal, neural tube, mesoderm

d) mesodermal, ectoderm, endoderm

e) endodermal, epidermis, blastocoelQuestion 3

During gastrulation in Xenopus, the blastocoel:

a) becomes the gut.

b) is filled with endodermal cells and disappears.

c) is filled with mesoderm and disappears.

d) does not change, but develops into what is called the archenteron.

e) is displaced, and its original location becomes an endoderm lined cavity, the archenteron, which is a precursor to the gut.

Question 4

The process in which the three germ layers form is called:

a) fertilization.

b) cleavage.

c) gastrulation.

d) organogenesis.

e) metamorphosis.Question 5

During gastrulation in Xenopus, the future mesoderm and endoderm move inside the embryo through the "blastopore"; in contrast, in chickens, gastrulation involves cells moving inward through the:

a) blastoderm.

b) yolk.

c) cleavage furrow.

d) primitive streak.

e) gut.

Question 6

In mammalian development, the embryo will form from which population of cells?

a) The blastocyst.

b) The inner cell mass.

c) The trophectoderm.

d) The blastocoel.

e) The extraembryonic membranes.Question 7

Maternal factors are:

a) energy rich proteins and lipids packaged into the vegetal pole.

b) hormonal influences encountered in the uterus in mammals.

c) mRNAs and proteins packaged into the egg by the mother, which act to control early development in the embryo.

d) genes contributed to the embryo by the maternal haploid genome.

e) components of the cortical granules which prevent polyspermy.Question 8

The role of maternal factors (such as Vg-1, Xwnt-1, and VegT) packaged into the vegetal region of the Xenopus oocyte is:

a) in establishing the future dorso-ventral body axis.

b) to allow the vegetal region to divide during cleavage.

c) to make the vegetal region denser, so that the egg always floats with its animal pole upward.

d) to specify the future animal-vegetal body axis.

e) to provide energy and nutrients for the developing embryo.Question 9

Between fertilization and the first cleavage division, actin filaments pull the cytoplasm of the frog egg toward the point of sperm entry in a process called:

a) cortical rotation.

b) dorsalization.

c) blastulation.

d) gastrulation.

e) determination.Question 10

In frogs, maternally packaged Xwnt-1 leads to nuclear localization of _____ in the _____, which in response signals to adjacent cells to become the _____.

a) β-catenin, Nieuwkoop center, Spemann organizer

b) nodal, signalling center, shield

c) Vg-1, vegetal region, Nieuwkoop center

d) sonic hedgehog, limb bud, posterior

e) GFP, mesoderm, muscle and boneQuestion 11

Remarkably, Vg-1 and wnt are used in both frogs and chicks to establish a body axis, although in chicks this is the antero-posterior axis instead of the dorso-ventral axis. What is the region of the chick embryo that is thus analogous to the Nieuwkoop center?

a) Area pellucida.

b) Blastoderm.

c) Primitive streak.

d) Posterior marginal zone.

e) Koller's sickle.Question 12

Although the vertebrate body plan outwardly displays a mirror-image symmetry with regard to left and right, the internal organs are not symmetrical. How does this left-right asymmetry develop?

a) The two cells of the Nieuwkoop center (at the 32-cell stage, see Figure 3.32) signal each other and become either left or right.

b) Maternal factors that determine left and right are packaged into the egg, just as dorsalizing factors are.

c) Differential release of Ca2+ ions on the left side leads to expression of Nodal and Pitx2 on the left.

d) Gravity determines the left-right axis: that side which is down becomes right and that side which is up becomes left.

e) No special mechanism is required, since the formation of an antero-posterior axis and a dorso-ventral axis automatically determines left and right.

Question 13

What is the difference between "fate" and "specification"?

a) If cells are transplanted from their normal region in an embryo to a different region in a recipient embryo, such cells will alter their fate, but not their specification.

b) Cell fate describes the allocation of cells to the germ layers, ectoderm, mesoderm, or endoderm, whereas specification describes the exact tissues that each cell will ultimately become.

c) The fate map of an embryo does not change during development -- the fate map of an egg is the same as the fate map of a late blastula -- whereas the specification map of an embryo changes continually as the embryo's development proceeds.

d) The specification state of a cell is determined by transplantation of cells to recipient embryos, whereas the fate of a cell is determined by the culture of those cells in an artificial medium.

e) The fate of a cell is determined by labelling that cell and following it during normal development, whereas the specification state of a cell is determined by culturing a cell in an artificial medium and observing what tissues form from it.

Question 14

A fate map of a Xenopus blastula, just before gastrulation begins, shows (Figure 3.44) that the top portion of the embryo will become ectoderm (skin and nerve), the central portion will become mesoderm (bone, muscle, and blood), and the lowest portion will become endoderm (gut). How is it that the endoderm and mesoderm, shown on the outside in the fate map, end up on the inside in the embryo after gastrulation?

a) The endoderm ends up inside through a process that can be visualized as if one pokes their finger into the bottom of a soft ball until the lowest endodermal portion ends up deep inside, the marginal zone mesoderm also ends up inside, and the ectoderm now encloses the entire outer surface.

b) The endodermal cells begin first to move into the embryo through the blastopore, displacing the blastocoel and forming a gut; as gastrulation proceeds, the blastopore spreads sideways and the mesoderm follows the endoderm in, ending up between the endoderm and the ectoderm.

c) The ectodermal cells divide and spread down over the rest of the embryo, so that the endoderm ends up on the bottom, ventral, surface of the embryo, and the mesoderm ends up around the middle, just as is shown in the fate map.

d) The three germ layers adopt their final positions through, first, the growth of the mesodermal marginal zone down over the endoderm, followed by, secondly, the growth of ectoderm down and over the mesoderm.

e) The cells, having already been fated to form endoderm and mesoderm, migrate directly into the interior of the embryo and take up residence in appropriate places.

Question 15

What property of the mammalian embryo permits the production of chimeric mice?

a) The inner cell mass is highly regulative, so that extra cells derived from the inner cell mass of a different embryo are incorporated without causing defects.

b) If half of the cells of the inner cell mass are removed and replaced with cells from half of a different embryo's inner cell mass, the embryo will heal and develop normally.

c) The embryo can develop outside the womb, making surgical manipulations possible.

d) Blastomeres separated at the two-cell stage will regulate and each forms a normal embryo.

e) Genetically determined pigmentation differences are incompatible in the developing embryo.

Question 16

If cells from the animal pole of a frog blastula (animal cap cells) are placed into contact with cells from the vegetal hemisphere, after removing the cells fated to form mesoderm, what is the result?

a) The cells regulate to form a normal embryo.

b) Animal cap cells are induced to form mesodermal derivatives.

c) Vegetal hemisphere cells are induced by the animal cap cells to form mesodermal derivatives.

d) An embryo forms with only ectodermal and endodermal derivatives.

e) Both animal and vegetal cells lose all specification and an undifferentiated ball of cells results.

Question 17

The "mid-blastula transition" is the point in development when:

a) translation of maternal mRNA is initiated.

b) cell determination becomes fixed.

c) cell division in the embryo ends.

d) transcription of zygotic genes begins.

e) blastocoel formation occurs.Question 18

What is the mechanism by which cells fated to be mesoderm form in the marginal zone of the Xenopus embryo?

a) Vegetal region cells migrate toward the animal pole and become mesoderm.

b) Cells in the marginal zone are fated to be mesoderm, but they do not become specified or determined as mesoderm until after they move internally during gastrulation.

c) Cells of the vegetal region are induced by their proximity to the animal region cells to become mesoderm.

d) Maternal factors packaged into the marginal zone act on these cells to instruct them to become mesoderm.

e) Secreted signals of the TGF-β family are released by the cells of the vegetal region and act on the adjacent cells of the marginal zone to instruct them to adopt a mesodermal fate.

Question 19

How is the Spemann organizer distinguished from the other mesodermal cells during induction by the cells of the vegetal region?

a) The cells of the Spemann organizer become different as they pass over the dorsal lip of the blastopore during gastrulation.

b) β-catenin, which has become localized to the nucleus in the Nieuwkoop center as a result of cortical rotation, turns on high levels of the TGF-β signalling molecule, Nodal, and this relatively high level distinguishes the adjacent cells of the Spemann organizer from the rest of the mesoderm.

c) The Spemann organizer is formed from cells of the Nieuwkoop center, which have migrated upward in the embryo.

d) BMP-4 signalling from ventral mesodermal cells toward the dorsal region specify the dorsal-most cells as organizer.

e) Signals from the animal region combine with signals from the vegetal region in the dorsal-most mesoderm, and specify those cells as the Spemann organizer.

Question 20

Patterning of the Xenopus mesoderm along the dorso-ventral axis involves an antagonistic relationship between chordin and BMP-4. Is there an analogy here to dorso-ventral patterning in the Drosophila embryo?

a) Yes, the Drosophila homolog of BMP-4, Decapentaplegic (Dpp), is antagonized by the Drosophila homolog of chordin, short gastrulation (Sog), in patterning of the dorso-ventral axis.

b) Yes, Drosophila also uses BMP-4 to specify ventral fates and chordin to specify dorsal fates.

c) Yes, the Drosophila Dorsal protein is identical to the vertebrate BMP-4 protein, and specifies the ventral region of the embryo.

d) No. the closest analogy from Drosophila would be the antagonism between Hunchback and Nanos, but neither of those are signalling molecules, and they act to pattern the antero-posterior axis.

e) No, insect development is totally different than that of real animals like frogs and chickens.

Question 1

The central nervous system is derived from _____, the axial skeleton is derived from _____, and the muscles of the trunk are derived from _____?

c) ectoderm, mesoderm, mesoderm

Question 2

What would be the effect on the timing of somite formation, if a piece of the pre-somitic mesoderm of a chick embryo is rotated by 180° and reinserted in its original position?

e) The timing of somite formation will be reversed in the rotated block only, proceeding from posterior to anterior, but the rest of the somites will form in a normal fashion, proceeding from anterior to posterior.

3

Relative to the primitive streak and Henson's node, somite formation in the chick embryo occurs:

a) Anterior to Henson's node, after the primitive steak has retracted past that point.

What observation might explain how somites originally become specified to form structures appropriate to their position along the antero-posterior axis?

d) Periodic waves of c-hairy1 are expressed in the presomitic mesoderm, such that cells in the more anterior somites will have been exposed to fewer waves of c-hairy1 than the cells in more posterior somites.

Question 5

What may be the molecular trigger that causes cells in the presomitic mesoderm to finally condense into somites?

b) The FGF gradient drops off in the region that is forming somites.

Question 6

Hox genes:

a) encode transcription factors which specify a position along the anterior-posterior axis in vertebrates.

Question 7

The effect of grafting an extra piece of notochord into a dorsal position adjacent to pre-somitic mesoderm is:

c) signals from the notochord will convert presumptive dermomyotome into sclerotome.

Question 8

The grafting of the dorsal lip of the blastopore from an  Xenopus gastrula onto the ventral side of an early embryo will result in:

c) The formation of two sets of anterior structures joined along the ventral axis: a two-headed embryo.

Question 9

The "default model" for neural tissue formation states that:

c) Neurectoderm formation is inhibited by the BMP proteins present throughout the early embryo, and this inhibition is relieved by BMP antagonists from the organizer, such as chordin.

Question 10

The use of segments as a developmental strategy in vertebrates is evident in:

d) both the axial skeleton and the hindbrain.

Question 1

In flies, frogs, and chicks, gradients of morphogens determine the future antero-posterior and dorso-ventral axes of the developing embryo. How is the antero-posterior axis determined in C. elegans?

e) Sperm entry leads to a reorganization of the cytoskeleton and redistribution of maternally packaged PAR proteins, which in turn determine the antero-posterior axis.

uestion 2

Do HOX genes play a role in the development of C. elegans?

d) Yes, but only one HOX gene is required in the embryo; the others provide positional identity in the larva.

uestion 3

What are the lin-4 and lin-14 genes of C. elegans?

a) Lin-4 encodes a miRNA that represses lin-14 translation, which in turn regulates the timing of larval development.

Question 4

The ability of the sea urchin embryo to regulate its development illustrates the fact that there are maternally-determined differences along the animal-vegetal axis that are

necessary for normal development. Which of the following statements about regulation in sea urchin embryos is consistent with that fact?

d) Blastomeres at the 4-cell stage each still possesses a portion of the original animal-vegetal axis, and if isolated will go on to form a fully formed, yet smaller, larva.

Question 5

In which way is the organizer region of the sea urchin similar to that in frogs?

c) The organizer accumulates β-catenin, which in turn activates the expression of cell-cell signaling molecules.

Question 6

Which one statement best describes gastrulation in sea urchins?

e) All of the above are true.

Question 7

In the ascidian, Styela, the yellow pigmented myoplasm marks cells fated to become muscle cells in the tail; however, at the molecular level, the key determinant of tail muscle seems to be:

c) the gene product of macho-1 gene.

Question 8

The role of the Brachyury gene in ascidians is similar to that in Xenopus in that:

d) Signaling that leads to induction of the mesoderm results in expression of theBrachyury gene in the mesoderm.

Question 9

Which statement describes Dictyostelium?

a) Dictyostelium cells can live as single, free-living cells, until they are stimulated by starvation to aggregate and sporulate.

Question 10

What is the role of cAMP in Dictyostelium development?

b) cAMP is secreted by individual cells in response to starvation, and serves to attract nearby cells resulting in formation of aggregate.

Question 1

In a comparison of plant and animal development, it is found that:

b) fully differentiated cells of plants are still totipotent, and will readily form a complete fertile plant, whereas the differentiated state of animal cells is difficult to reverse.

Question 2

Why has the diploid genome been an advantage in studying the development ofArabidopsis?

c) The diploid genome allows genetic analysis of development, in a manner analogous to the genetic analysis that has been done with Drosophila.

Question 3

The fate map of the Arabidopsis embryo at the heart stage indicates that:

d) although none of the adult structures have formed, the regions that will give rise to the meristems, which will in turn give rise to adult structures, can be identified.

Question 4

One of the earliest events in Arabidopsis development is formation of the _____ axis, in response to a gradient of _____.

a) apical-basal, auxin

Question 5

The genetic analysis of Arabidopsis development was strongly influenced by genetic analysis of Drosophila development, and as is the case in Drosophila, genes that influence development are often named for:

e) the phenotype observed when the gene is mutated.

Question 6

Maintenance of the shoot meristems in adult Arabidopsis plants relies on which of the following mechanisms?

d) All of the above are involved in specification and maintenance of shoot meristems.

Question 7

Refer to Figure 6.18 on page 241 in the text: in the lower portion of the figure, where would leaf primordium number 7 appear?

d) Adjacent to leaf primordium number 6, on the proximal side of primordium number 4.

Question 8

Which of the following describes the pathway in Arabidopsis by which day-length is translated into a signal that coverts a vegetative shoot meristem into a floral meristem?

e) a through d above describe, in order, the pathway by which shoot meristems are turned into floral meristems.

Question 9

What is meant by the word 'whorl' in discussing floral meristems?

b) Flowers consist of four different types of organs, which occur in concentric rings called 'whorls'.

Question 10

In what way are the homeotic genes of flowering plants similar to those of Drosophilaand other animals?

c) Mutations in the homeotic genes of flowers cause transformation of one organ into another.

Question 11

What is the phenotype of a mutation in the AGAMOUS homeotic gene of Arabidopsis? (Recall, genes are often named for the mutant phenotype.)

a) AGAMOUS mutants fail to restrict the expression of class A genes, resulting in four whorls composed of sepals and petals, with no stamens or carpels.

Question 12

How is the ABC model for floral identity in Arabidopsis reminiscent of the models for homeotic gene function derived from studies in Drosophila?

d) In both organisms, the homeotic genes interact, so that it is often the combination of genes present that is critical in unambiguously specifying structures in the adult.

uestion 1

Previous chapters have focused on the establishment of embryonic axes and the specification of cellular identity. At the molecular and cellular level, how does morphogenesis differ from those processes?

d) The formation of embryonic axes and the specification of cell fates rely heavily on cell-cell signaling events, and their influence over gene expression patterns, whereas morphogenesis relies primarily on cell-cell adhesion and cell motility.

Question 2

Adherens junctions play in important role in development; they are composed of:

a) Cadherins linked to other cadherins extracellularly, and to actin filaments intracellularly.

Question 3

If embryos are disaggregated with chemicals or proteases, and the individual cells are mixed together in culture, what will happen?

b) The cells will often sort themselves so that like cells are together.

Question 5

Which of the following is the only true statement regarding compaction in the mouse embryo?

d) All of the above are true of compaction in the mouse embryo.

Question 6

How do the endodermal cells of the sea urchin embryo carry out gut formation during gastrulation?

c) Changes in cell shape initiate the invagination; convergent extension extends the sheet of cells into the blastocoel, and finally, filopodia make contact with the future mouth region and pull the tip of the gut to that point.

Question 7

Contrast involution, epiboly, and convergent extension.

b) Involution is the movement of cells inside the embryo as a coherent sheet, epiboly is a flattening and spreading of epithelial cells to increase the amount of surface they cover, and convergent extension is movement of cells toward an axis to extend that axis.

Question 8

During gastrulation in the frog, the very first cells to move into the interior of the embryo through the blastopore come from the surface layer of cells in the marginal zone; they will become:

c) endoderm.

Question 9

Gastrulation in sea urchins, Drosophila, and Xenopus all begin with a change in cell shape, in which the apical surface of an epithelial sheet contracts. This process is called:

d) invagination.

Question 10

In Xenopus, the mesoderm moves in through the blastopore by rolling around the dorsal lip in a process called:

a) involution.

Question 11

In Xenopus, the elongation of the mesoderm toward the anterior results from the intercalation of cells during a process called:

b) convergent extension.

Question 12

In chicks, the formation of the neural tube relies on what cell biological processes?

c) Both changes in cell shape in the neural plate and changes in adhesion molecule expression in the neural tube are required during formation of the neural tube.

Question 13

Neural crest cells will become:

e) All of the above are derived from neural crest cells.

Question 14

Neural crest cells taking the dorso-lateral route will become:

e) melanocytes.

Question 1

Which of the following cells would be considered differentiated?

d) Muscle cell.

Question 2

Differentiated cells express the genes and proteins characteristic of their final identity in the adult, and that identity can be altered only under special circumstances. How does the concept of differentiation, as described here, differ from the concept of determination?

c) Determined cells will continue to follow their fate if grafted into a different place in a host embryo, even though they do not yet express the genes and proteins characteristic of their final fate.

Question 3

What is the role of stem cells with regard to the function of adult tissues and organs?

a) Stem cells are undifferentiated cells that divide asymmetrically, giving rise to one daughter that remains a stem cell and one daughter that will differentiate to replace damaged and worn out cells in the adult tissue or organ.

Question 4

The immunoglobulin genes are expressed in B-cells, and the β-globin gene is expressed in red blood cells. What manipulations might be carried out to get the β-globin gene to be expressed in B-cells?

c) The cis-regulatory region of an immunoglobulin gene could be combined with the coding region of the β-globin genes, and this artificial gene would then express β-globin in B-cells.

Question 5

Imagine that in an attempt to get the β-globin gene to be expressed in B-cells (see question 4 above), the transcription factors (GATA-1 and GATA-2) known to control the β-globin gene in erythrocytes were introduced into B-cells, yet the β-globin gene was not expressed. What is a likely explanation for this result?

b) The β-globin gene in the B-cells is packaged into heterochromatin, and the erythrocyte transcription factors are insufficient to remodel that chromatin into an active state.

Question 6

What type of cell-cell signaling protein exerts its effect in gene expression through a receptor that is a transcription factor?

d) Hydrophobic molecules like steroid hormones and retinoic acid.

Question 7

What is the developmental pathway by which the hematopoietic stem cell gives rise to a macrophage?

e) The hematopoietic stem cell must first generate a cell of the myeloid lineage (as opposed to the lymphoid lineage), then a granulocyte/macrophage progenitor, then a monocyte, and finally a macrophage.

Question 8

Hematopoietic stem cells can be isolated and grown in culture; if one wished to control their differentiation into either neutrophils or macrophages, what colony stimulating factors could be used?

a) First, GM-CSF and IL-3 would be added to trigger formation of the granulocyte/macrophage lineage; then, the addition of either G-CSF or M-CSF would select between further differentiation as neutrophils or macrophages, respectively.

Question 9

What is globin gene switching?

d) Globin gene switching refers to the transition, during fetal development, from the production of hemoglobin containing ε-globin, to γ-globin, to β-globin.

Question 10

What do "V", "J", and "C" mean in the context of the genes for immunoglobulins?

c) There are several V and J exons in an immunoglobulin gene; one of each is selected during a rearrangement in the DNA to produce an immunoglobulin gene capable of being expressed; the V and J segments that are not selected are lost from the genome.

Question 11

Where are the stem cells that renew the epithelium of the gut found?

d) Near the bottom of the crypt.

Question 12

What happens if you introduced the gene myoD into fibroblast cells growing in culture?

a) The fibroblasts will express muscle-specific proteins, fuse, and form functional muscle in culture.

Question 13

In what way are mrf4, myoD, and the other muscle-inducing genes similar to the homeotic genes of Drosophila?

b) mrf4, myoD, and the others encode 'master-switch' transcription factors, which initiate a cascade of gene expression that leads to the differentiation of cells.

Question 14

Neural crest cells that follow a dorso-lateral route of migration under the skin will become melanocytes; how is their differentiation into melanocytes triggered during their migration?

d) The cells in the skin express a ligand (stem cell factor, SCF, also known asSteel) on their surface, which interacts with a receptor (Kit, also known as white spotting) on the surface of the neural crest derived cells; this interaction triggers their differentiation as melanocytes.

Question 15

What is the difference between apoptosis and necrosis?

a) Apoptosis is a controlled program of cellular destruction; necrosis is cell death due to damage.

Question 16

What is the role of the caspases in apoptosis?

e) Caspases are proteases that carry out the controlled destruction of the cell's components during apoptosis.

Question 17

What important lesson for the mechanisms of development can we derive from the ability to clone frogs by nuclear transfer?

a) That the selective gene expression seen in differentiated cells does not result from an irreversible loss of genes, or their potential for expression.

Question 18

Recently, it was reported that adult, differentiated cells can be made to behave as pluripotent stem cells by the introduction of a few genes, one of which was Oct4. What was the rationale for this experiment?

b) Oct4 expression is one of the requisites for the maintenance of pluripotent embryonic stem cells in culture.

Question 1

Cartilage (bone-forming tissue) and connective tissue of the vertebrate limb form from:

b) the mesodermal mesenchyme of the limb bud, derived from lateral plate ectoderm.

Question 2

Which of the following correctly describes the sequence of events by which the position of limbs along the antero-posterior axis of vertebrates is specified?

a) Hox gene expression in the mesoderm activates Wnt signaling, which turns on FGF expression and formation of the limb bud.

Question 3

Removal of the apical ridge leads to:

b) formation of structures proximal to the apical ridge, but no formation of new distal structures.

Question 4

The grafting of a second polarizing region into the anterior of a limb bud results in:

e) a new axis can be formed if the second polarizing region is large, and a second full set of digits can form with mirror-image orientation to the normal set of digits.

Question 5

In Chapter 4, it was proposed that activation of Hox genes along the antero-posterior axis in vertebrates might be related to the time spent in Henson's node as it retreats posteriorly: cells expressing anterior Hox genes spend the least amount of time in the node, while cells expressing posterior Hox genes have spent progressively more time in the node. What aspect of limb development may involve a similar mechanism?

c) The amount of time spent in the progress zone may determine which Hox genes are expressed along the proximo-distal axis of the growing limb, and hence the identity of structures formed.

Question 6

The muscle-forming cells of the vertebrate limb come from

c) mesodermal cells that migrate into the limb bud from the somites

Question 7

Cells of the muscle forming region of the somite, the myotome, express Pax3; Pax3activates expression of myoD and myf5, but muscle differentiation does not occur until the cells stop dividing. When they enter the limb bud, Pax3 is downregulated, division ceases, and differentiation begins. At this point, what gene is the next to be activated as the cells differentiate into muscle?

b) myogenin

Question 8

If apoptosis in the developing limb were blocked, what feature of a normal limb would not form?

e) The digits would be connected by webbing, and would not be separated.

Question 9

In thinking about the development of the wing imaginal disc of Drosophila, what is the significance of "compartments"?

d) Since cells in adjacent compartments have different lineage histories, adjacent compartments can adopt different fates and differentiation patterns, as in the formation of the anterior and posterior portions of the wing blade.

Question 10

Engrailed comes to be expressed in posterior compartments during Drosophilaembryogenesis; what is the consequence of engrailed activation of hedgehog (Hh) signaling from the posterior compartment of the wing disc?

a) Hh activates decapentaplegic (Dpp) signaling at the compartment boundary; Dppthen acts as a morphogen to pattern the development of veins in the wing blade.

Question 11

Keeping in mind the fact that genes are often named for the phenotype of a mutation in that gene, what might be the phenotype of a mutation of the Distal-less gene ofDrosophila?

c) Distal-less mutants would form only proximal structures, like the coxa (proximal end) of the legs without a tarsus (distal end).

Question 12

The development of drugs to block the activity of vascular endothelial growth factor (VEGF) has been applied to the control of the growth of cancers. What is the rationale for such a strategy?

b) Tumor cells produce VEGF to stimulate angiogenesis in their vicinity, and tumors cannot continue to grow without this supply of blood.

Question 13

Heart development begins as:

c) a pair of tubes in the lateral plate mesoderm that move together and fuse to form a single tube that will become the heart.

Question 14

Teeth form from:

d) a combination of oral epithelium and neural crest-derived mesenchyme in the jaw.

Question 15

Hedgehog signaling at the compartment boundary in the Drosophila wing disc leads to the expression of what signaling molecule in the adjacent anterior cells?

c) decapentaplegic

Question 16

The segmental identity of imaginal discs is determined by:

a) Hox genes

Question 17

The heart forms from:

b) lateral plate mesoderm

Question 18

The kidney forms from:

c) mesoderm

Question 1

In the development of the nervous system, which is the correct order of events?

b) First, cells must be specified to be neurons, second, the neurons must migrate to their final position, third, these neurons must make connections with their targets, and fourth, the neurons refine their synaptic connections.

Question 2

In Drosophila, the neurectoderm is located ventrally during gastrulation, while in mice or frogs, the neurectoderm is located dorsally. Which statement best describes how the two systems are similar or different?

d) Although the invertebrate nervous system is a ventrally located nerve cord, and the vertebrate spinal cord is located dorsally, homologous genes play a role, and neurons are ultimately specified through a process of lateral inhibition in both cases.

Question 3

How does lateral inhibition work to specify individual neurons in the neural epithelium of invertebrates and vertebrates?

a) Prospective neurons first arise in a cluster, but then, by chance, one cell will come to signal more strongly through Delta and Notch than its neighbors and become the only neuron in the cluster, by inhibiting its neighbors' specification as neurons.

Question 4

The ventricular proliferative zone is:

d) a region of cell division in the neural tube.

Question 5

What is the relationship between dorso-ventral patterning of the neural tube and patterning of the somites?

c) Sonic hedgehog from the notochord and floorplate of the neural tube confers ventral fates on both the neural tube and the somite, while BMPs confer more dorsal fates.

Question 6

What role, if any, do Hox genes play in specification of neuronal fate?

b) Different combinations of Hox genes specify the identities of neurons along the antero-posterior axis.

Question 7

What is the role of semaphorins and Eph ligands in development of the nervous system?

b) The semaphorins and Eph ligands act as signals for the outgrowth of neuronal growth cones; in general, both lead growth cones to turn away.

Question 8

What is the consequence for the ability of motor neurons to find their correct targets, if a section of the spinal cord is rotated, so that the antero-posterior axis is reversed?

a) Anterior motor neurons enter the limb in a bundle in the posterior instead of the anterior, but then take novel pathways to find the correct anterior muscles to innervate.

Question 9

What does the experiment in which a frog's eye is rotated tell us about the spatial relationships between the retina and the tectum?

c) When the right retina makes connections to the left tectum, nasal (anterior) neurons go to the posterior tectum, and temporal (posterior) neurons go to theanterior tectum.

Question 10

The "synaptic cleft" of a neuromuscular junction is

d) the space between the plasma membrane of a neuron on the pre-synaptic side of the synapse, and the plasma membrane of the muscle cell on the post-synaptic side of the synapse.

Question 11

Do neurons make synapses with other neurons?

d) Yes, however, the connections neurons make with each other differ from those they make with muscle cells in that cell-cell adhesion molecules link the pre-synaptic and post-synaptic membranes together.

Question 12

Why can't babies see well when they are first born?

a) The multiple connections between the retina and the visual cortex present at birth become refined in response to visual stimuli, through changes in connectivity and cell death.

Question 1

What generalization can be applied to the pole plasm of Drosophila, the P-granules of C. elegans, the yolk-free vegetal cytoplasm of Xenopus, and the localized mRNA for vasain zebrafish?

d) All mark the special region of cytoplasm, the germplasm, that is involved in specification of germ cells.

Question 2

Why is meiosis required for germ cell formation, yet is never used by somatic cells?

a) Meiosis is the cell division process that produces haploid products.

Question 3

Two human disorders, Prader-Willi syndrome and Angelman syndrome, occur when the mother contributes a copy of chromosome 15 that contains a small deletion in a specific region. Why does this small deletion not behave as a recessive allele, that is, why is its loss not made up for by the good copy of the region on the paternally contributed chromosome 15?

b) The father's copy of chromosome 15 has genes in the region of the deletion that are imprinted, and thus inactive; in the absence of any active copies of these genes, development cannot proceed normally.

Question 4

What is the 'acrosomal reaction'?

c) The acrosomal reaction is the digestion of the zona pellucida, permitting the sperm to contact the egg.

Question 5

What is the cortical reaction, and why is it important?

e) The cortical reaction is the release of the cortical granules after sperm entry, which converts the vitelline membrane into the fertilization membrane which blocks polyspermy.

Question 6

In humans, an individual with an XXY chromosomal complement will develop as:

a) a male.

Question 7

Secretion of Müllerian-inhibiting substance by Sertoli cells:

e) causes the Müllerian duct to regress by apoptosis in males.

Question 8

In what way, if any, does the chromosomal determination of sex differ in Drosophila and humans?

b) In humans, the Y chromosome determines maleness, but in Drosophila, the ratio of X chromosomes to autosomes determines maleness or femaleness.

Question 9

What is the molecular activity of the Sex-lethal protein of Drosophila?

c) Sex-lethal controls the splicing of specific mRNAs such that certain proteins required for female development are produced only in females.

See page 441 of the book for more information.

Question 10

In mammals, dosage compensation is carried out by:

c) inactivating one X chromosome in females by condensation as heterochromatin.

Question 1

In developmental biology, what is meant by the concept of 'growth'?

e) All of the above are mechanisms by which growth occurs.

Question 2

Many cells in the body divide only rarely, if at all; neurons, red blood cells, and keratinocytes are extreme examples. In which portion of the cell cycle would such cells be considered to be?

c) G0 phase

Question 3

The size of a cell is generally controlled by the amount of DNA in the nucleus: the more DNA, the larger the cell. What do experiments in which the amount of DNA is doubled (tetraploidy in salamanders) tell us about growth control?

a) The animals grow to a normal size, and contain only half as many cells, indicating that growth is regulated at the level of absolute size, rather than cell number.

Question 4

Disease, injuries, and birth defects that compromise the function of the pituitary may lead to decreased stature (height). What treatment might be prescribed, and what would be its rationale?

b) Loss of pituitary function could lead to decreased growth hormone production, and hence short stature; recombinant human growth hormone might be prescribed.

Question 5

Adult human bone:

c) grows only at the growth plates between the epiphysis and the diaphysis.

Question 6

What are osteoblasts?

e) Osteoblasts are bone-forming cells that derive from stem cells in the bone marrow, and therefore have no lineage relationship to chondrocytes.

Question 7

Cancer is believed to often arise from stem cells, rather than fully differentiated cells. Which of the following are consistent with this view?

e) All of the above are reasons that cancer cells may more readily arise from stem cells than from fully differentiated cells.

Question 8

Is there a difference between oncogenes and tumor suppressor genes?

d) Yes, oncogenes are mutated versions of genes that promote abnormal cell division (such as ras and myc), whereas tumor suppressor genes are genes that normally hold cell division in check when it is not appropriate (such as Rb and p53).

Question 9

Insects such as Drosophila undergo three molts before becoming a pupa and undergoing metamorphosis. Molting, which is also called 'ecdysis', is controlled by what hormone?

a) ecdysone

Question 10

Metamorphosis of amphibians is triggered by environmental cues that act on the:

c) hypothalamus.

Question 11

What does it tell us about aging that cells from different organisms are capable of a fixed number of divisions in culture, and that number of divisions reflects the relative life-span of the organism?

b) In each organism, the cells seems to be capable of a genetically determined number of divisions, after which the organism undergoes senescence and dies.

Question 12

Which of the following is consistent with a model for aging in which stresses leading to DNA damage cause senescence and aging?

d) All of the above are consistent with a model for aging based on DNA damage.

Question 1

Epimorphosis is regeneration through:

c) the reinitiation of division in existing cells, followed by patterning, as occurs in amphibians such as newts.

Question 2

When the blastema forms after amputation of a newt limb, what processes must the cells undergo in order for regeneration to occur?

e) Dedifferentiation, cell division, transdifferentiation, and formation of an AER-like function are all involved.

Question 3

If the nerve supply to a newt limb is severed before amputation, how will this affect regeneration?

d) A blastema will form but will not grow, and regeneration will fail.

Question 4

"Intercalary growth" in a regenerating amphibian limb means that if a distal blastema is grafted to a proximal stump:

b) the stump grows out to regenerate proximal structures, until the positional values of the blastema are produced, at which time the distal blastema takes over and completes outgrowth of distal structures.

Question 5

How does the dose-dependence of retinoic acid treatment support the notion that a gradient of retinoic acid can act as a morphogen along the proximo-distal axis in the limb?

d) Treatment with high levels of retinoic acid causes a distal blastema to be respecified as a proximal blastema, and regeneration of a full limb may be initiated from proximal values.

Question 6

What is especially exciting about research into regeneration in zebrafish?

c) Limited regeneration of heart muscle can occur in zebrafish, and the ability to study zebrafish genetically will enhance our ability to understand the genetic basis of regeneration.

Question 7

Which statement correctly characterizes regeneration in the mammalian nervous system?

a) In some instances, peripheral nerves can regenerate an axon if cut, such as when motor neurons regenerate axons to make correct connections with muscles.

Question 8

Is regeneration in Hydra similar to regeneration in vertebrates, or is it fundamentally different in some way?

a) Regeneration in Hydra occurs through a repatterning of existing cells by morphallaxis, unlike regeneration in vertebrates, which occurs through epimorphosis.

Question 9

We learned in Chapter 3 (page 114) that treatment of Xenopus embryos with lithium dorsalizes the embryos by interfering with cell-cell signaling pathways. What, if anything, is the effect of lithium on Hydra, and what might we infer about its mechanism of action?

c) Lithium causes the formation of extra basal discs, which we might infer arise through interference with cell-cell signaling pathways.

Question 10

What molecular marker of head identity is found in the apical tip of a Hydra during head regeneration?

e) Wnt

Question 1

Ontogeny is:

d) the development of an individual organism

Question 2

In humans, the branchial arches have evolved to give rise to:

a) bones in the human ear.

Question 3

Which is true?

a) Limbs evolved from fins.

Question 4

The absence of limbs in snakes may be attributable to the evolution changes in:

d) Hox gene expression.

Question 5

Hedgehog family genes specify the _____ position in both vertebrate and insect wings.

d) posterior

Question 6

The Hox gene complexes of mice and other mammals have evolved by:

c) the duplication of the ancestral cluster.

Question 7

Which provides an example of the evolution of new forms through the modification of preexisting structures?

e) All of the above.

Question 8

Changes in the timing of developmental events is called:

c) heterochrony.

Question 9

A key evolutionary event that allowed the evolution of the bilaterally symmetric triploblasts from the common ancestor of the triploblasts and the diploblasts would have been:

d) the evolution of the mesoderm.

Question 10

How would you expect HOX genes to be expressed in millipedes, where all segments bear similar legs, when compared to insects?

a) The leg specifying HOX genes would be expressed in all leg-bearing segments