Exam 21: Development of Multicellular Organisms

A cat's left eye was covered during the critical period of development after eye opening. At the age of 6 months, a radioactive tracer molecule was injected into the right eye and allowed to reach the primary visual cortex. The cortex was then sectioned and subjected to autoradiography to reveal the ocular dominance columns. Which stripes would you expect to be wider: the dark stripes due to radioactivity (D) or light stripes (L)? Write down D or L as your answer.

Cortical rotation following fertilization in X. laevis places the …(1) pole at the point of sperm entry, while Wnt11 mRNA is transported to the …(2) pole.

Indicate whether each of the following descriptions better applies to egg-polarity genes (E), gap genes (G), pair-rule genes (P), or segment-polarity genes (S). Your answer would be a four-letter string composed of letters E, G, P, and S only, e.g. SSGG. ( ) Mutations in these genes show a maternal effect. ( ) Mutations in these genes leave the embryo with only half the number of normal segments. ( ) Mutations in these genes produce a normal number of segments but with part of each segment replaced by a mirror-image duplicate of other parts of the segment. ( ) Mutations in these genes can eliminate one or two groups of adjacent segments altogether.

Fill in the blank in the following paragraph describing collective cell rearrangements. Do not use abbreviations. "Cells form lamellipodia and attempt to crawl over one another, essentially pulling their neighbors inward into a narrow zone. This is accompanied by elongation along the long axis of the narrow zone. This process of … depends on Wnt signaling and is observed multiple times during the development of a vertebrate."

The qualitative graph below shows the molecular changes accompanying vernalization in the flowering plant Arabidopsis thaliana. Indicate which curve (A to D) in the graph better represents the temporal changes in each of the following variables. Your answer would be a four-letter string composed of letters A to D only, with each letter used once, e.g. BACD. ( ) Level of Coolair noncoding RNA ( ) Level of Flowering locus C (FlC) gene product (transcriptional repressor) ( ) Level of Flowering locus T (Ft) gene product (transcriptional activator) ( ) Level of repressive chromatin marks at the FlC locus

The gene clusters known as the Bithorax complex and the Antennapedia complex contain…

After reaching sexual maturity, the nematode Caenorhabditis elegans normally doubles in size within about two weeks. This doubling is mainly due to …

Which of the following evolutionary changes better explains morphological differences between different animals despite many common molecular mechanisms governing their development?

The simplified drawing below depicts early stages of animal development. Indicate which letter (A to E) in the drawing corresponds to each of the following terms. Your answer would be a five-letter string composed of letters A to E only, e.g. ECDBA. ( ) Blastula ( ) Ectoderm ( ) Endoderm ( ) Mesoderm ( ) Gastrula

Robo3.1 is an alternative splice form of Robo3 that blocks the reception of Slit signals by the Robo1 and Robo2 receptors. Considering the guidance of commissural neurons crossing the ventral midline in the embryonic spinal cord of a vertebrate, would you expect Robo3.1 activity to increase (I) or decrease (D) as the growth cone crosses the midline? Write down I or D as your answer.

Which of the following is NOT true regarding cell-type specification in developing animals?

Sort the following organisms from the least to the most degree of asymmetry in the unfertilized egg (i.e. pre-defined axes of polarization). Your answer would be a three-letter string composed of letters A to C only, e.g. BCA. (A) M. musculus (B) D. melanogaster (C) X. laevis

The following schematic drawings show an epithelial sheet. Which example shows a mutant with planar-cell-polarity defects but no other defects?

In the following fate map for the Xenopus blastula, indicate which zone in the map (A to D) better corresponds to each of the following fates. Your answer would be a four-letter string composed of letters A to D only, e.g. DCAB. ( ) Lung ( ) Blood ( ) Brain ( ) Skin

Indicate true (T) and false (F) statements below regarding developmental timing in animals. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT. ( ) Cell-division cycles generally serve as an intracellular timer that controls the timing of cellular differentiation. ( ) Developmental transitions are often regulated by microRNAs. ( ) Intracellular developmental programs are often followed even if the cells are taken from the developing embryo and maintained in culture. ( ) Timing of developmental transitions can be coordinated by cell-cell interactions as well as globally by hormones.

Stromal cell-derived factor 1 (SDF1) is a secreted protein that plays a major role in guiding the migration of various cells during development. It binds to a G-protein-coupled receptor on the surface of the migrating cell, which in turn activates a trimeric G protein containing a Gᵢ subunit. Pertussis toxin (PTX) modifies and inactivates the Gᵢ subunit. What would you expect to observe if migrating cells are treated with PTX?

The axons and dendrites of neurons that lack DSCAM1 altogether …

Imagine a morphogen gradient established from left to right in a field of cells in a developing tissue, as shown in the following schematic diagram. Below a first threshold of morphogen concentration, cells do not respond to the morphogen and express gene "red" by default. Cells exposed to morphogen concentrations above this threshold respond by expressing gene "white" instead, while those exposed to even higher concentrations, above a second threshold, express gene "blue." As shown, the initial pattern resembles a French flag with equally wide blue, white, and red expression domains. With no other change, if the diffusion rate of the morphogen is increased (by a modification that decreases its affinity for heparan sulfate proteoglycans, for example), the gradient profile changes from the gray curve to the black curve, as indicated. Under this new condition, indicate whether each of the following would be expected to increase (I), decrease (D), or remain unchanged (U) in its range. Your answer would be a three-letter string composed of letters I, D, and U only, e.g. UUI. ( ) Blue expression domain ( ) White expression domain ( ) Red expression domain

Which of the following is correct regarding the regulation and maintenance of Hox gene expression in Drosophila?

Sort the following primary axes in the order that they are established during the development of Xenopus laevis. Your answer would be a three-letter string composed of letters A to C only, e.g. ACB. (A) A-P (B) D-V (C) A-V