A strain of Drosophila known as dunce produces one-half the amount of cAMP phosphodiesterase found in wild-type flies, which causes a learning defect. Another strain of Drosophila known as rutabaga produces a defective adenylyl cyclase protein (one of the AC types expressed in most cells) and also causes a learning defect. A dunce–rutabaga double mutant fly has relatively normal learning. Explain these curious observations?

How do we know that the mutant Bar-eye phenotype in Drosophila is due to a duplicated gene region rather than to a change in the nucleotide sequence of a gene?

Recently, scientists constructed a transgene that expresses a mutant form of Drosophila histone H3 inwhich lysine 27 in the histone tail was changed to methionine (H3K27M). Expression of the H3K27Mtransgene results in aberrant development of fruit fliesbecause of inappropriate expression of many differentgenes. Explain this finding.

Based on the partial diploid sketched shown in Figure 3, where cross-hatched rectangles and the red bar indicate mutations that inactivate that particular genetic element of the operon, state if expression of Lacl (Lac repressor) and LacZ (Beta-Galactosidase) is (select one of the options below for each genetic element and briefly justify your answer): constitutively ON (in the presence/absence of lactose) constitutively OFF (in the presence/absence of lactose) • inducible by lactose • not enough information given to conclude • none of the above FIGURE 3: lacl laco lacz- lacY lacl laco lacz lacY

As we have learned in this chapter, the Nanos protein inhibits the translation of hunchback mRNA, lowering the concentration of Hunchback protein at the posterior end of a fruit-fly embryo and stimulating the differentiation of posterior characteristics. The results of experiments have demonstrated that the action of Nanos on hunchback mRNA depends on the presence of an 11-base sequence that is located in the 3′ untranslated region (3′ UTR) of hunchback mRNA. This sequence has been termed the Nanos response element (NRE). There are two copies of NRE in the 3′ UTR of hunchback mRNA. If a copy of NRE is added to the 3′ UTR of another mRNA produced by a different gene, that mRNA is repressed by Nanos. The repression is greater if several NREs are added. On the basis of these observations, propose a mechanism for how Nanos inhibits Hunchback translation.

Regarding noncoding RNA, which of the following statements is false?   HOTAIR RNA works as a scaffold that binds specific protein regulators at its two ends.   Many long noncoding RNAs work in epigenetic regulation of gene expression.   Most regulatory long noncoding RNAs work as trans-acting regulators.   HOTAIR RNA is produced by a gene in the HOXC homeobox gene cluster at 12q13 but can regulate multiple genes within the HOXD gene cluster on chromosome 2.   Noncoding RNAs are mostly involved in translation processes.

The genes described below are part of the yeast mating signal transduction pathway that signals the presence of extracellular alpha pheromone to the nucleus. These genes are listed in the order they function in the pathway. STE3 encodes alpha pheromone receptor STE4 encodes the ß subunit of a heterotrimeric G protein STE7 encodes a protein kinase STE12 encodes a transcription factor Loss-of function-mutations in any of these genes are sterile. In addition, gain-of-function mutations can be isolated in these genes. For which gene would a loss of function mutation suppress gain-of-function mutations in any of the other three genes. STE3 STE7 STE12 STE4

In the introduction to this chapter, we discussed the role of famine during early prenatal development and how, through epigenetic effects, it influenced the health of individuals as adults. One effect that has been observed in people who were conceived during the Dutch Hunger Winter is that they suffer more cognitive decline later in life. If these individuals were autopsied after death, what differences might you expect to see in the chromatin of their brain cells? What do the mouse studies of cognition and epigenetic effects suggest?

CD3 is a signaling protein that is typically found only in the plasma membrane of immune system T lymphocytes. CD3 is composed of several different polypeptides, including a gamma chain, CD3γ. Scientists analyzed the promoter of the CD3γ chain gene for regulatory sequences that might have positive or negative effects on expression of the gene. The scientists cloned fragments of the CD3γ gene that included the first transcribed nucleotides plus up to 789 nucleotides of upstream regulatory sequences into plasmids in which the gene for the firefly enzyme luciferase immediately follows the fragments. The plasmids were then introduced into a line of T lymphocytes (Figure 1), and the cells were allowed to grow for a short while. Because the regulatory sequences of the CD3γ gene immediately precede the luciferase gene in the plasmids, the activity, either positive or negative, of the regulatory sequences affected the amount of luciferase gene expression by the T lymphocytes. Luciferase…