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Question 1

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

a) ectoderm, mesoderm, endoderm

b) mesoderm, endoderm, endoderm

c) ectoderm, mesoderm, mesoderm

d) all are derived from mesoderm

e) all are derived from ectoderm

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?

a) There would be no effect because the embryo would regulate and development would proceed normally.

b) Antero-posterior development would be blocked at that point, and more posterior structures would fail to form.

c) The rotated mesoderm would degenerate and a gap would form in the antero-posterior pattern.

d) The rotated mesoderm will reverse the gradient of somite formation, so that somite formation posterior to the rotated mesoderm will begin in the posterior and move forward to meet the previously formed somites.

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.

Question 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.

b) Posterior to Henson's node, as cells from the lateral portions of the epiblast move in through the primitive streak to become mesoderm.

c) Adjacent to Henson's node, as the primitive streak migrates toward the anterior of the embryo.

d) Somite formation occurs simultaneously along the axis, after Henson's node has fully retracted.

e) Somites form before the primitive streak forms, and guide the path of Henson's node.

Question 4

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

a) If pre-somitic mesoderm is rotated, the somites form in a reversed order.

b) Somites in the anterior of the embryo form before somites in the more posterior regions.

c) A gradient of retinoic acid exists that emanates both anteriorly and posteriorly from the somites.

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.

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

Question 5

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

a) A gradient of retinoic acid exists that emanates both anteriorly and posteriorly from the somites.

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

c) 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.

d) Signaling from the receptor Notch is required for somite formation.

e) Different HOX gene combinations are expressed along the antero-posterior axis of the embryo.

Question 6

Hox genes:

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

b) make signaling molecules used during somite formation.

c) control the formation of vertebrae in mice, but are not found in other animals.

d) are expressed such that the low-numbered genes, a1, b1, and so on, are expressed in the posterior regions, whereas high-numbered genes are expressed in more anterior regions.

e) are expressed only in the mesoderm.

Question 7

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

a) The pre-somitic mesoderm will degenerate.

b) Somites will form but fail to differentiate.

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

d) The somite will be converted almost entirely to muscle-forming cells.

e) The somite is incorporated into the neural tube.

Question 8

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

a) The formation of two separate and independent embryos.

b) The formation of two complete embryos joined along the ventral axis.

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

d) The formation of two sets of posterior structures joined along the ventral axis: a two-tailed embryo.

e) No effect: only dorsal lips from early embryos have organizer activity.

Question 9

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

a) No mechanism is required to form nervous tissue in the embryo; it forms unless signals direct development of epidermal tissue.

b) Neural tissue formation is the default state, such that special induction is required to form mesoderm, endoderm and epidermis, but not neurectoderm.

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

d) The induction of neural tissue is the default state in embryos, and all other inductions are special.

e) FGF is the sole inducer of neural ectoderm.

Question 10

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

a) the endoderm.

b) the axial skeleton, only.

c) the hindbrain, only.

d) both the axial skeleton and the hindbrain.

e) the ventral epidermis.

Oxford University Press, Online Resource Centre, Chapter 04.

Chapter 04

Instructions