Biology 52 exam IV, May 5, 2006

You have two hours.  Feel free to draw pictures to help answer the questions. 


1) [8 points] Suppose that you are designing a screen for mutants affecting embryonic patterning in Drosophila.  You treat a population of male flies with a chemical mutagen.  a) Outline what you would then do to find individual flies with mutations of interest, starting with this mutagenized population and as many wild-type flies as you want.  Include in your description which flies are heterozygous or homozygous for the new mutations you are screening for. 









b) Some of the mutations you might find would have a maternal effect.  How would you recognize individuals with maternal-effect mutations? 




2) [20 points] The embryonic patterning defects of some Drosophila mutants can be rescued by injections of cytoplasm from wild-type embryos.  How would each of the following embryos develop:

a) bicoid mutant embryo (from a bicoid mutant mother):

i) untreated


ii) injected at the anterior end with cytoplasm from the anterior end of a wild-type embryo


iii) injected in the middle with cytoplasm from the anterior end of a wild-type embryo


b) toll mutant embryo (from a toll mutant mother):

i) untreated


ii) injected on the dorsal side with cytoplasm from the dorsal side of a wild-type embryo


ii) injected on the dorsal side with cytoplasm from the ventral side of a wild-type embryo


c) In the injections in a and b, at what developmental stages would you need to obtain wild-type donor cytoplasm, and at what stage would you need to inject cytoplasm into the recipient mutant embryo to produce the effects you indicated?




d) In a and b, what molecule(s) could you inject to produce the same effects on patterning?

3) [9 points] a) Describe the phenotypes of the following Drosophila mutants.  In each case indicate whether the mutation is dominant or recessive, and the biochemical function of the protein encoded by the corresponding wild-type gene.


a) proboscipedia


b) bithorax


c) polycomb



4) [20 points] a) On the following diagram of a wild-type Arabidopsis inflorescence apex,

i) label each of the meristems and lateral organs; 

ii) Indicate which cells are dividing most actively. 









b) On the following diagram, indicate which cells express

            i) the WUSCHEL gene,

ii) the AGAMOUS gene,

iii) the LEAFY gene. 







c) How would each of the following mutations (or combinations of mutations) affect the number and identities of flower organs formed?

            i) apetala2 apetala3


            ii) apetala1


            iii) sepallata1 sepallata2 sepallata3


iv) clavata3


5) [6 points]  A great diversity of flower forms are found in nature and in greenhouses.  Suggest how regulation of flower development in each of the following flower forms may differ from regulation of Arabidopsis flower development.  Assume in each case that the same regulatory genes are present in the indicated species as in Arabidopsis. 

a) azaleas with two whorls of petals instead of one. 



b) dogwood trees with white or pink bracts (a bract is a leaf-like organ found immediately beneath the flower in some plants.)



c) Acacia trees in which flowers are produced by the shoot apical meristems, which then grow leaves again in the following season




6) [12 points]  a) The following diagrams show an Arabidopsis gynoecium and a close-up diagram of an ovule within the gynoecium.  On the diagrams, indicate how a pollen grain fertilizes the ovule.  Include the site of pollination, the route by which sperm is delivered, and where fertilization takes place.  Indicate the ploidy of each of the cells in the ovule both before and after fertilization. 










b) Maize plants that are homozygous for an ea1 mutation are female sterile, although the female gametopyhyte has normal anatomy, and they also have have normal pollen production and function.  On the following diagram of a maize female gametophyte, indicate i) which cells express the EA1 gene and ii) where the EA1 protein is present. 






iii) What goes wrong during fertilization to cause the ea1 mutant plant to be female sterile?





iv) Do you expect that a heterozygous EA1/ea1 plant would be sterile or fertile?   


7) [12 points] a) Sketch an antibody protein.  Indicate the antigen binding region, and which part of the antibody the i) V and ii) Ca heavy chain gene segments encode.




b) What are the functions of the part of the protein encoded by these segments?

            i) V


            ii) Ca


c) Describe two types of genetic changes that occur in antibody genes prior to a secondary immune response?  In which cells do these changes occur? 








8) [13 points] A scientist makes a vaccine using an attenuated virus that can grow slowly in human cells but does not normally cause disease.  The vaccine is injected into an individual who mounts a cellular immune response.  a) Describe how lymphocyte cells mount the immune reaction against the antigen.  Include in your answer i) which genes are rearranged, ii) which cells are induced to proliferate, iii) the molecular recognition events that provide specificity of response, and iv) how the body actually gets rid of the infection.  v) Indicate which events occur before and which occur after immunization. 















b) How might the immune system of someone with AIDS respond to this vaccination?






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