University of Calgary

Faculty of Science

Final examination

CMMB 403

December 18, 1999 Time: 3 hours

Sign the class list.

Fill in front page of both exam booklets.

Label one booklet for Dr. Brook and one for Dr. O'Connor.

Put the answers to Dr. Brook's questions in one booklet (labeled as such), and the answers to Dr. O'Connor's questions in the other booklet (labeled as such).

If you do not understand a question, ask the instructor.

The number of marks allotted for each question is shown in brackets after the question.

The total number of marks is 55.


I. Dr. O'Connor's Questions

O1. (a) Briefly describe the timing and major events of the mid-blastula transition that occurs in Xenopus embryos. (3)

(b) Considering the evidence presented in class, how is the timing of the MBT probably regulated? (2)

(c) Briefly describe three pieces of evidence that support this model. (If you cannot remember the exact evidence we discussed in class, briefly describe three experiments that would address this question.) (3)

(d) Speculate on molecular mechanisms which might account for an abrupt versus gradual initiation of zygotic transcription. (2)

O2. Pick a major developmental regulatory gene which, given its role in development, could theoretically act as a proto-oncogene, and briefly explain how and why. (3)

(DO NOT use any of the examples given in the cancer lecture)

O3. Considering the model for vertebrate limb development we discussed in class, what would be the effect of excising wing limb field mesenchyme from a chick neurula, and replacing it with its anterior/posterior polarity reversed? Explain why and how this effect would occur. (7)

O4. Consider the models for vertebrate limb and muscle development we discussed in class. Starting at the somite stage, trace in detail the development of a muscle fiber in a chick wing, in terms of regulatory factors, migration, and differentiation. (15)



II. Dr. Brook's Exam Questions:

B1. Choose a or b (8 points)

a. What is the evidence that bicoid encodes a maternally localized anterior determinant that has a concentration dependent effect on cell fate determination?


b. There are four protein gradients established early in Drosophila embryogenesis from maternally localized mRNAs. Explain how the four gradients form and what their role is in regulating gene expression.

B2. Choose a or b (6 points)

a) In wild-type flies, Antennapedia gene expression is usually highest in the first leg imaginal discs, absent in more anterior imaginal discs and only weakly expressed in more posterior structures. Some dominant mutations of Antennapedia result in the ectopic expression of high levels of Antennapedia protein in all imaginal discs. In flies bearing these mutations, the limbs of the head segments (the antennae, the proboscis and the maxillary palps) are transformed into legs similar to those normally found in the first thoracic segment. However, the legs, wings and halteres of the second and third thoracic segments, and the abdominal structures are all unaffected. Based on your knowledge of homeotic gene regulation in the embryo, explain the phenotypes caused by the Antennapedia mutation.


b) The even-skipped stripe 2 enhancer is a 130 bp DNA fragment that has several binding sites for activating proteins (hunchback and bicoid) and several binding sites for repressing proteins (giant and Krüppel). Outline the genetic and molecular experiments that led to the following conclusions:

  1. That the 130 bp fragment is the regulatory element responsible for even-skipped stripe 2 expression.
  2. That bicoid, hunchback, giant and Krüppel act to regulate even-skipped expression in stripe 2.
  3. That the regulation of even-skipped stripe 2 expression by bicoid, hunchback, giant and Krüppel is through direct interaction of the proteins encoded by those genes with the even-skipped enhancer.

B3. Short answer (6 points) Choose 3 of the following (2 points each)

a) Distal-less, even-skipped, bicoid, hunchback (zygotic), gurken, hedgehog, wingless, engrailed

    1. Place the list genes in the correct order of action during segmentation.
    2. Name three of the genes that specify fate in a concentration dependent manner.
    3. What is the term used for a molecule that can specify cell fate in a concentration dependent manner?

b) Name two genes that control the development of the dorsal-ventral wing axis. What sort of proteins do they encode and what is their function in wing development?

c) What is the major difference between clones produced by mitotic recombination and clones produced by flip-out transgenes?

d) What does co-linearity mean with respect to the homeotic genes?

e) What is a maternal effect mutation?

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