When performing in vitro mutagenesis, a vector is used that may contain a positive marker (e. g., a gene for resistance against the antibiotic neomycin) and a negative marker, such as the thymidine kinase gene. cells that carry the latter will die when exposed to a drug called ganciclovir. if a researcher exposed stem cells to a targeting vector with these two markers, and subsequently treated them with neomycin and then ganciclovir, which would be true of the surviving cells? a. any surviving cells will have been correctly targeted (i. e., the gene of interest will have been removed).b. half of the surviving cells will still contain the gene targeted for inactivation, whereas in the remaining half this gene will have been removed. c. any surviving cells will not carry either the positive or negative markers. d. any surviving cells will still contain the original, targeted gene (i. e., these cells could not be used to generate knockout mice)

Over the past 60 years, many amphibian species have experienced significant population declines and some species have become extinct. scientists suspected that local human activities such as the destruction of wetlands, regional pollution, and deforestation were the main reasons for these losses. however, research over the past 20 years reveals significant amphibian population declines in protected areas of the world, such as nature preserves and parks. these global declines suggest widespread problems including increased ultraviolet radiation, acid rain, and disease. in switzerland, for example, 14 of the 20 native amphibian species are threatened with extinction. chytridiomycosis is a fungal disease first identified in 1998 as a cause of massive amphibian deaths. in some severely impacted populations, a few individuals have survived, perhaps because of some natural resistance. if these resistant individuals continue to survive and prosper, new resistant populations might emerge. this would be an example of the founder effect artificial selection genetic drift natural selection sexual selection

Amouse that is homozygous for the dominant trait has the genotype . it has . a mouse that is homozygous for the recessive trait has the genotype . it has . image of fur color of mice

What do lava flows made of aa indicate about the type of volcanic eruption that occurred? a. the eruption was viscous. b. the eruption was pyroclastic. c. the eruption was explosive. d. the eruption was quite. !