Researchers know that Fru-M controls male sexual behavior in Drosophila because inappropriate Fru-M expression in females causes them to behave like males: Such females display male behaviors that are oriented toward other females. a. Describe a fru mutation that could cause expression of Fru-M in females. b. Describe a gene construct that scientists could generate and insert into Drosophila females that would have the same effect as the mutant you described in (a).

Figure shows that in the lac operon, both the operator $\left(\mathrm{o}_1\right)$ and the binding site for $\mathrm{CRP}-\mathrm{cAMP}$ show rotational symmetry. This is not true of the promoter (the RNA polymerase binding site) as a whole. Why do you think the promoter does not exhibit rotational symmetry?

In an effort to determine the location of an operator site for a negatively regulated gene, you have made a series of deletions within the regulatory region. The extent of each deletion is shown by the line underneath the sequence, and the resulting expression from the operon (i = inducible; c = constitutive; - = no expression is also indicated).

. . . G G A T C T T A G C C G G C T A A C A T G A T A A A T A T A A . .

. . C C T A G A A T C G G C C G A T T G T A C T A T T T A T A T T . .

a. What can you conclude from these data about the location of the operator site?

b. Why do you think deletions 2 and 4 show no expression?

In Drosophila subobscura, the presence of a recessive gene called grandchildless $(\mathrm{gs})$ causes the offspring of homozygous females, but not those of homozygous males, to be sterile. Can you offer an explanation as to why females and not males are affected by the mutant gene?

a. The original constitutive operator mutations in the lac operon were all base changes in $O_{1} .$ Why do you think mutations in $O_{2}$ or $O_{3}$ were not isolated in these screens? b. Explain how a mutagen that causes small insertions could produce an $O^{c}$ mutation. c. Would the $O^{c}$ mutation described above in part b be sensitive to $\mathrm{lacl}^{s} ?$ Why or why not?

You are studying a transgenic mouse strain that expresses a GFP reporter gene under the control of cisacting regulatory elements that normally control a gene needed for the early development of mice. Previous evidence from transcriptome sequencing (RNA-seq) indicates that mRNA for the gene of interest can be identified between days 8.5 and 10.5 of gestation. In your strain, GFP fluorescence can be seen from about day 8.75 until at least day 12. a. Explain the discrepancy between mRNA and protein expression. b. Would you expect GFP protein expression to indicate more accurately the normal onset of activity for this gene or the normal cessation of this gene's activity? Explain.

The hunchback gene, a gene necessary for proper patterning of the Drosophila embryo, is translationally regulated. The position of the coding region within the transcipt is known. How could you determine if if the sequence within the 5' UTR or 3' UTR, or both, are necessary for proper regulation of translation?

Interestingly, imprinting can be tissue-specific For example, a gene that is maternally imprinted infetal placental tissue is not imprinted at all in the fetal heart Guided by the diagram in Fig. 16.22 a on P. 560 , suggesta mechanism that could explain the tissue specificity of in printing (Hint Remember that a genenay liave nultiple enhancers that allow expression in different tissues )

Solve by using the strategy Guess and Test. When a number is subtracted from half of its own square, the result is 60. What is the number?

Let $m\angle H$ be an acute angle. Use a calculator to approximate the measure of $\angle H$ to the nearest tenth of a degree. $\sin H = 0.2$

Antibodies are currently available that will bind specifxcally to DNA fragments containing 5-methylcytosime but not to DNA lacking this modified nucleotide. How could you use these antibodies in conjunction with the ChlP-Seq technique outlined in Fig. 16.17 on p. 556 to look for inprinted genes in the human genome?

Follow the expression of a paternally imprinted gene through three generations. Indicate whether the copy of the gene from the male in generation I in the accompanying diagram is expressed in the germ cells and somatic cells of the individuals listed.

a. generation I male (I-2): germ cells

b. generation II daughter (II-2): somatic cells

c. generation II daughter (II-2): germ cells

d. generation II son (II-3): somatic cells

e. generation II son (II-3): germ cells

f. generation III grandson (III-1): somatic cells

g. generation III grandson (III-1): germ cells

The modular nature of eukaryotic activator proteins gave scientists an idea for a way to find proteins that interact with any particular protein of interest. The idea is to use the protein-protein interaction to bring together a DNA-binding region with an activation region creating an artificial activator that consists of two polypeptides held together noncovalently by the interaction. The method is called the yeast two-hybrid system, and it has three components. First, the yeast contains a construct in which

$$UAS_G$$

(an enhancer-like sequence that binds the activator Gal4) drives the expression of an E. coli lacZ reporter (encoding the enzyme

$$\beta \text { -galactosidase }$$

) from a yeast promoter. Second, the yeast also expresses a fusion protein in which the DNA-binding domain of Gal4 is fused to the protein of interest; this fusion protein is called the "bait." The third component is a cDNA library made in plasmids, where each cDNA is fused in frame to the activation domain of Gal4, and these can be expressed in yeast cells as "prey" fusion proteins. How could you use a yeast strain containing the first two components, along with the plasmid cDNA expression library described, to identify prey proteins that bind to the bait protein? How is this procedure relevant to the goal of finding proteins that might interact with each other in the cell?

a. You want to create a genetic construct that will express GFP in Drosophila. In addition to the GFP coding sequence, what DNA element(s) must you include in order to express this protein in flies if the construct were integrated into the Drosophila genome? Where should such DNA element(s) be located? How would you ensure that GFP is expressed only in certain tissues of the fly, such as the wing? b. In making your construct, you insert the GFP coding region plus all of the DNA elements required by the answer to part (a) excepting the enhancer in between inverted repeats found at the end of a particular transposable element. Because all th DNA sequences located between these inverted repeats can move from place to place in the Drosophila genome, you can generate many different fly strains, each with the construct integrated at a different genomic location. You now examine animals from each strain for GFP fluorescence. Animals from different strains show different patterns: some glow green in the eyes. others in legs, some show no green fluorescence, etc. Explain these results and describe a potential use of your construct.