* not completed

. Somites will give rise to

heart and blood correct incorrect

internal organs of the abdomen correct incorrect

the vertebral column and skeletal muscles correct incorrect

the spinal cord. correct incorrect

* not completed

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

area pellucida correct incorrect

blastoderm correct incorrect

posterior marginal zone correct incorrect

Koller's sickle correct incorrect

* not completed

. The positioning of the dorso-ventral axis in Xenopus is determined by _____, while the positioning of the antero-posterior axis in chicks is determined by _____.

gravity; point of sperm entry correct incorrect

maternal factors in both cases correct incorrect

position in the egg chamber; gravity correct incorrect

the point of sperm entry; gravity. correct incorrect

* not completed

. At the morula stage during mammalian embryonic development, the 'outer' cells, which will form trophectoderm, express ________; whereas 'inner' cells, which will form inner cell mass, express ________.

Oct4; Cdx2 correct incorrect

BMP; FGF correct incorrect

Cdx2; Oct4 correct incorrect

FGF; BMP correct incorrect

* not completed

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

ectoderm, mesoderm, endoderm correct incorrect

mesoderm, endoderm, endoderm correct incorrect

ectoderm, mesoderm, mesoderm correct incorrect

all are derived from mesoderm correct incorrect

* not completed

. 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?

there would be no effect because the embryo would regulate and development would proceed normally correct incorrect

antero-posterior development would be blocked at that point, and more posterior structures would fail to form correct incorrect

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 correct incorrect

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 correct incorrect

* not completed

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

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

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

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

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

* not completed

. What observation suggests that positional values along the antero-posterior axis are specified in the pre-somitic mesoderm before somite formation begins?

A number of genes have a cyclic pattern of expression in the pre-somitic mesoderm correct incorrect

Somites in the anterior of the embryo form before somites in the more posterior regions. correct incorrect

A graft of a portion of pre-somitic mesoderm to another level on the axis will develop into structures typical of its original position. correct incorrect

The FGF gradient drops off in the region that is forming somites. correct incorrect

* not completed

. What is the initial signal that causes cells in the pre-somitic mesoderm to condense into somites?

High level of retinoic acid signaling. correct incorrect

Low level of FGF/Wnt signaling. correct incorrect

Notch signaling. correct incorrect

Expression of different Hox gene combinations along the antero-posterior axis of the embryo. correct incorrect

* not completed

. Hox genes

encode transcription factors that specify a position along the anterior-posterior axis in vertebrates correct incorrect

encode signaling molecules used during somite formation correct incorrect

control the formation of vertebrae in mice, but are not found in other animals correct incorrect

are expressed only in the mesoderm correct incorrect

* not completed

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

the pre-somitic mesoderm will degenerate correct incorrect

somites will form but fail to differentiate correct incorrect

signals from the notochord will convert presumptive dermomyotome into sclerotome correct incorrect

the somite will be converted almost entirely to muscle-forming cells correct incorrect

* not completed

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

the endoderm correct incorrect

the axial skeleton, only correct incorrect

the hindbrain, only correct incorrect

both the axial skeleton and the hindbrain correct incorrect

* not completed

. 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?

The two cells of the Nieuwkoop center signal each other and become either left or right. correct incorrect

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

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

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

* not completed

. Which of the following is NOT involved in left-right asymmetry of vertebrates?

Calcium signaling correct incorrect

Nodal correct incorrect

Epidermal growth factor correct incorrect

Pitx2 correct incorrect