Question 1

The amphibian egg is radially symmetric along the animal-vegetal axis. What &#34;breaks&#34; this symmetry?&#10;A) Localization of maternal RNAs to the vegetal pole&#10;B) Fertilization&#10;C) Localization of maternal RNAs to the animal pole&#10;D) Cleavage

Accepted Answer

Fertilization introduces a sperm entry point, which breaks the radial symmetry of the amphibian egg by defining the future dorsal-ventral axis, leading to the establishment of the animal-vegetal axis.

Question 2

Removing the ventral blastomeres from a four-cell amphibian embryo gives rise to an embryo lacking which tissue?&#10;A) Notochord&#10;B) Neural tube&#10;C) Somites&#10;D) Gut

Accepted Answer

The ventral blastomeres in a four-cell amphibian embryo contribute to the formation of endodermal tissues, including the gut. Removing these cells would result in an embryo lacking gut tissue.

Question 3

What is the dorsal vegetal region that induces the Spemann-Mangold organizer in an amphibian embryo?&#10;A) Animal cap&#10;B) Nieuwkoop center&#10;C) Marginal zone&#10;D) Vegetal center

Accepted Answer

The Nieuwkoop center is the region in the dorsal vegetal part of the amphibian embryo that induces the formation of the Spemann-Mangold organizer, which is crucial for the development of the primary body axis.

Question 4

Which of the options given would not be an expected way of forcing premature onset of the mid-blastula transition?&#10;A) Injecting extra DNA into the egg&#10;B) Injecting extra cytoplasm into the egg&#10;C) Forcing two sperm to enter the egg&#10;D) Removing some cytoplasm from the egg

Accepted Answer

Injecting extra cytoplasm into the egg would not directly affect the DNA-to-cytoplasm ratio or the nuclear-to-cytoplasmic ratio, which are key factors in triggering the mid-blastula transition (MBT). The MBT is primarily influenced by changes in these ratios, such as those that would occur through the addition of extra DNA (A), the entry of additional sperm which adds more DNA (C), or the removal of cytoplasm (D), which effectively increases the nuclear-to-cytoplasmic ratio even without adding more DNA.

Question 5

Which of the following does not send signals that directly induce and pattern the mesoderm?&#10;A) Vegetal blastomeres&#10;B) Animal blastomeres&#10;C) Dorsal mesoderm&#10;D) Ventral mesoderm

Accepted Answer

Animal blastomeres are primarily involved in forming the ectoderm and do not directly induce and pattern the mesoderm. The mesoderm is induced and patterned by signals from the vegetal region of the embryo, not the animal region.

Question 6

Which of the following is not true of the role of BMPs in mesoderm patterning?&#10;A) Overexpression of BMPs ventralizes the embryo&#10;B) Introduction of a dominant-negative BMP receptor ventralizes the embryo.&#10;C) BMP function is inhibited by organizer signals&#10;D) BMPs are signaling ligands that bind to cell-surface receptors on target cells.

Accepted Answer

BMPs play a crucial role in the dorsal-ventral patterning of the embryo. Overexpression of BMPs leads to ventralization (A is true), while the introduction of a dominant-negative BMP receptor would block BMP signaling, leading to dorsalization, not ventralization, making B incorrect. BMP function is indeed inhibited by organizer signals (C is true), and BMPs are signaling ligands that bind to cell-surface receptors on target cells (D is true).

Question 7

Which of the following is the only structure induced If one performs the organizer transplantation experiment with a blastopore lip from a late stage gastrula?&#10;A) Head&#10;B) Trunk&#10;C) Tail&#10;D) Brain

Accepted Answer

In a late stage gastrula, the organizer region has shifted its inductive potential to primarily induce posterior structures, such as the tail, rather than anterior structures like the head or brain.

Question 8

Which of the following is not a secreted organizer protein?&#10;A) Chordin&#10;B) Noggin&#10;C) Follistatin&#10;D) BMP

Accepted Answer

BMP (Bone Morphogenetic Protein) is not a secreted organizer protein; it is a target of the organizer proteins such as Chordin, Noggin, and Follistatin, which inhibit BMP signaling to promote neural development.

Question 9

Transplanting a piece of anterior mesoderm to the blastocoel of a host frog embryo will induce which of the following structures?&#10;A) Head&#10;B) Trunk&#10;C) Tail&#10;D) Spinal cord

Accepted Answer

The anterior mesoderm is known to induce the formation of head structures in the developing embryo. This is because the anterior mesoderm contains signals that specify head development during early embryogenesis.

Question 10

In the zebrafish embryo, what is the equivalent of the Xenopus organizer?&#10;A) Shield&#10;B) Node&#10;C) Blastopore lip&#10;D) Plate

Accepted Answer

In zebrafish embryos, the structure functionally equivalent to the Xenopus organizer is the shield. This region plays a crucial role in early development, directing the formation of the body axis and organizing the development of various tissues, similar to the role of the organizer in Xenopus embryos.

Deck 4: Laying Down the Vertebrate Body Plan: Xenopus and Zebrafish