12. The primary pair-
15. If you diagram these results, you will see that the deletion of a gene that functions posteriorly allows the next most anterior segments to extend in a posterior direction. Deletion of an anterior gene does not allow extension of the next most posterior segment in an anterior direction. The gap genes activate Ubx in both thoracic and abdominal segments, whereas the abd-
18.
A pair-
Look for expression of the mRNA from the candidate gene in a repeating pattern of seven stripes along the A–
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No. An embryo mutant for the gap gene Krüppel would be missing many anterior segments. This effect would be epistatic to the expression of a pair-
21.
The homeodomain is a conserved protein domain containing 60 amino acids found in a significant number of transcription factors. Any protein that contains a functional homeodomain is almost certainly a sequence-
The eyeless gene (named for its mutant phenotype) regulates eye development in Drosophila. You would expect that it is expressed only in those cells that will give rise to the eyes. To test this prediction, visualization of the location of eyeless mRNA expression by in situ hybridization and the Eyeless protein by immunological methods should be performed. Through genetic manipulation, the eyeless gene can be expressed in tissues in which it is not ordinarily expressed. For example, when eyeless is turned on in cells destined to form legs, eyes form on the legs.
Transgenic experiments have shown that the mouse Small eye gene and the Drosophila eyeless gene are so similar that the mouse gene can substitute for eyeless when introduced into Drosophila. As in the answer to part b, when the mouse Small eye gene is expressed in Drosophila, even in cells destined to form legs, eyes form on the legs. (However, the “eyes” are not mouse eyes, because Small eye and eyeless act as master switches that turn on the entire cascade of genes needed to build the eye—
25. GLP-