Biology 441 Spring 2011, Second Exam Key

Each question was worth 5 points total.

1) Circle which 3 of the following have the same symmetries A N I X Z H % * @ &
There are two valid answers: NZ% or IXH

2) What is this symmetry? How many fold, what symmetry?
NZ% have two-fold rotational symmetry; IXH have two-fold reflection symmetry

3) Who is this building named in honor of?
H.V. Wilson
- 1 point for each missing initial.

4) What was his major discovery?
sponges separated into individual cells sort out to re-form the anatomical pattern

5) How did he misinterpret his discovery?
d) he thought the cells were re-differentiating

6) Cancer cells of several kinds have been reported to sort out from random mixtures with normal cells of the same differentiated cell type, with the cancer cells accumulating nearer the surface of the cell aggregates, and the normal cells collecting into solid blobs in the interior: How would Malcolm Steinberg's hypothesis interpret this result? (what does it tell us about how cancer cells are abnormal?)
b) cancer cells are less adhesive than normal cells

7) What is the symmetry of a set of four identical quadruplet armadillo embryos, after each quadruplet develops its right-left asymmetry?
4-fold rotational symmetry

8) What two hypothetical mechanisms have been proposed for breaking displacement symmetry in developing embryos?
reaction-diffusion or Turing
clock and wavefront

9) If you put one chick embryo directly on top of another during somite formation, and made time-lapse videos of when and where each embryo continued to form somites, which theory would be supported if the somites of the embryos then became synchronized, but not spatially aligned?
clock and wavefront

And which theory would be supported by observations that locations of new somites became spatially aligned (tended to be directly over each other, even if not forming simultaneously)?

10) What are the five major families of genes that control development of fly anatomy?
a) polarity (bicoid, nanos) b) gap (Krüpple) c) pair-rule (even-skipped, fushi terazu) d) segment polarity (engrailed) e) homeotic selector (antennapedia, bithorax)

11) What are two specific examples of homeotic mutants that occur in Drosophila?
And what specific abnormality of the body structure does each mutation produce?
antennapedia: anterior imaginal discs form legs rather than antennae
bithorax: two second thoracic segments are formed, resulting in two pairs of wings rather than one

12) What kinds of animals have hox genes?
(nearly) all multicellular animals
-2 for insects and vertebrates, -3 for just vertebrates, -4 for just insects, -4 for any answer that included "except salamanders"

13) Describe and name the remarkable, unexplained correlation that exists between the locations of effects in mutations of hox genes, relative to the locations of hox genes on chromosomes?
colinearity of chromosomal order and body region affected

14) Do embryos tend to develop more symmetry as they develop, or the reverse?
they lose symmetry

Give two examples:
There are quite a few correct choices here. The best answers included a specific event in development and told what symmetry change occurred.

15) What are two examples of variables in anatomical structures that are second order tensors?
stress (tension), strain, curvature - any two of these

16) Sketch a sea urchin embryo early during gastrulation, and diagram the relative amounts and directions of curvatures of different parts of its anatomy at this stage.
full credit for correct basic shape with all major curvatures marked
no credit for drawing something that was not a sea urchin gastrula
1 point bonus for identifying the saddle point at the blastopore

17) The main usefulness of bioassays is?
d) To discover what chemicals serve particular normal functions

18) Osmotic pressure belongs to which class of variables?
a) scalar

19) What is a meristem?
region of plants where mitoses are occurring; -2 points for not mentioning mitosis or cell division
Name two kinds
either root / shoot, or apical / lateral

20) During the exam, time lapse videos will be shown of Dictyostelium slugs aggregating from amoebae, crawling from place to place, and then forming a fruiting body.
Please tell when each of the following symmetries occur, during these events.

Axial symmetry (an infinite number of planes of reflection symmetry, along one axis)?
aggregating mass of cells, fruiting body - 2 points for naming at least one of these

One plane of reflection symmetry? slug - 2 points

Dilation symmetry?slugs or fruiting bodies in groups, aggregating amoebae - 1 point for any

1 point bonus for listing all of the correct answers, and no incorrect ones