6. Suppose a particular gene is required for early development and also later for development of a particulartissue, such as the adult nervous system. By generating a homozygous mutant clone in that tissue of a heterozygote, researchers can circumvent the lethalitythat would result if the entire animal is homozygousfor a loss-of-function mutation in that gene.A technique called MARCM (Mosaic Analysiswith a Repressible Cell Marker) was developed to enable Drosophila geneticists to generate homozygousmutant cell clones that are marked by the presence of areporter protein such as GFP. Marker expression enables the investigator to observe clearly the mutantphenotype within a clone of mutant cells. This technique relies on a yeast protein called Gal80 that is anegative regulator of the Gal4 protein described previously in Solved Problem II. Gal80 binds to Gal4 andprevents it from activating transcription. The idea ofMARCM is that Gal4/UASG-driven GFP expression isblocked by Gal80 throughout the fly, except within thehomozygous mutant clone where the Gal80-expressingtransgene is lost by mitotic recombination.a. Diagram the chromosomes and the mitotic crossover that generate a homozygous m− mutant clonemarked by GFP expression.b. How could you restrict the clones to the adult nervous system?
6. Suppose a particular gene is required for early development and also later for development of a particular
tissue, such as the adult nervous system. By generating a homozygous mutant clone in that tissue of a heterozygote, researchers can circumvent the lethality
that would result if the entire animal is homozygous
for a loss-of-function mutation in that gene.
A technique called MARCM (Mosaic Analysis
with a Repressible Cell Marker) was developed to enable Drosophila geneticists to generate homozygous
mutant cell clones that are marked by the presence of a
reporter protein such as GFP. Marker expression enables the investigator to observe clearly the mutant
negative regulator of the Gal4 protein described previously in Solved Problem II. Gal80 binds to Gal4 and
prevents it from activating transcription. The idea of
MARCM is that Gal4/UASG-driven GFP expression is
blocked by Gal80 throughout the fly, except within the
homozygous mutant clone where the Gal80-expressing
transgene is lost by mitotic recombination.
a. Diagram the chromosomes and the mitotic crossover that generate a homozygous m− mutant clone
marked by GFP expression.
b. How could you restrict the clones to the adult nervous system?
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