25. Selectable markers offer a clever way to identify cells or organisms that have undergone rare transformation events. When creating targeted gene knockouts in mice, a population of embryonic stem (ES) cells are transformed with a vector containing a neomycin-resistance gene flanked by DNA sequences that match the targeted gene. This provides selection for cells that have integrated the neomycin-resistance gene into a chromosome. A tk+ gene is also included in the vector, but it is outside the regions with homology to the targeted gene. The purpose of the tk+ gene is to select against ectopic insertions, as well as to select against cells in which _________ crossovers occurred between the vector and the targeted gene.
a) single
b) double
Answer is b) double .
Double crossovers occurs between between the vector and targeted gene. Single crossovers will be effective in deleting genes. tk means thymidine kinase. For better result double crossovers are always required.
25. Selectable markers offer a clever way to identify cells or organisms that have undergone rare...
2. A dominant allele H reduces the number of body bristles that Drosophila flies have, giving rise to a “hairless” phenotype. In the homozygous condition, H is lethal. An independently assorting dominant allele S has no effect on bristle number except in the presence of H, in which case a single dose of S suppresses the hairless phenotype, thus restoring the "hairy" phenotype. However, S also is lethal in the homozygous (S/S) condition. What ratio of hairy to hairless flies...
1.When comparing ex vivo and in vivo gene therapy techniques, which of the following statements is true? A. Ex vivo therapy only relies on bacterial plasmids as vectors, whereas in vivo therapy only relies on viral vectors. B. During ex vivo therapy, the gene is transcribed (but not translated), whereas with in vivo therapy, the gene is both transcribed and translated. C. In vivo therapy typically involves the injection of a new gene directly into an individual, whereas ex vivo...