Hydrangea plants produce flowers that can be either blue or pink in color. The flowers will be blue if they are grown in acidic soil (having a pH of 5.5 or less) or pink if they are grown in soil with a neutral to basic pH of 6.5 and up. What can be concluded from this information?

If the coding region of a gene (the exons) contains 2,100 base pairs of DNA, would a missense mutation cause a protein to be shorter, longer, or the same length as the normal 700 amino acid proteins? What would be the effect of a nonsense mutation? A sense mutation?

Two genes associated with breast cancer, BRCA1 and BRCA2, were discovered in 1994 and 1995, respectively, and shortly thereafter, were patented by Myriad Genetics, a company based in Utah. Under the patents, testing for mutations in these genes could only be performed by Myriad, at costs from 300 to 3,000. Myriad also patented the process of analyzing the results of such tests, preventing anyone who obtains the sequence of their BRCA genes by other means (which itself would probably be patent infringement) from interpreting the information. The idea that genes can be patented has been a contentious issue from the beginning. Patents are not granted for products of nature, meaning that genes inside the body are not patentable, but biotech companies successfully argued that by removing a gene from the human body, purifying it, and then obtaining its DNA sequence, they created something not found in nature, and which is therefore a patentable invention. The U.S. Patent Office found the argument persuasive, but opponents argue that genes are parts of our bodies and can be identified but not invented. Biotech companies argue that without the protection offered by patents, they would have no incentive for research and development of diagnostic tests. In Europe, patents for BRCA1 and BRCA2 were revoked in 2004 because they did not meet the standards for a patent. After more than a decade of legal disputes, the patents were partially restored in 2008 on a very restricted basis. In the United States, a lawsuit, focused on the patents for the BRCA genes, was filed in May 2009. The suit challenges the basic idea that genes are patentable. In November 2009, the judge ruled that the lawsuit can proceed, and the case is moving forward. In March 2010, a federal court invalidated Myriad Genetics patent on these genes. In August 2011, the U.S. Court of Appeals reversed the lower courts decision and ruled that gene sequences isolated from cells are not a product of nature and are therefore patentable. The case went to the U.S. Supreme Court, which ordered the appeals court to reconsider the case. The Federal Appeals Court did not change its decision, and the case once again, went to the U.S. Supreme Court. A unanimous decision in June 2013 invalidated Myriads patents on the basis that isolating a gene from nature does not make it patentable. This is a landmark decision on gene patenting with widespread ramifications for the biotechnoloogy industry. Will this decision reduce the incentives for companies to invest in new diagnostic tests that would be used by cancer victims or those with serious genetic disorders?

Neanderthal Hair Color The MC1R gene regulates pigmentation in humans (Sections 14.1 and 15.1 revisited), so loss-of-function mutations in this gene affect hair and skin color. A person with two mutated alleles for this gene makes more of the reddish melanin than the brownish melanin, resulting in red hair and pale skin. DNA extracted from two Neanderthal fossils contains a mutated MC1R allele that has not yet been found in humans. To see how the Neanderthal mutation affects the function of the MC1R gene. Carles Lalueza-Fox and her team introduced the allele into cultured monkey cells (FIGURE 26.16). FIGURE 26.16 MC1R activity in monkey cells transgenic for an unmutated MC1R gene, the Neanderthal MC1R allele, or the gene for green fluorescent protein (GFP). GFP is not related to MC1R. 1. How did MCR1 activity in monkey cells with the mutant allele differ from that in cells with the normal allele?

Variations in Phenotype Expression A genetic disorder characterized by falling asleep in genetics lectures is known to be 20% penetrant. All 90 students in a genetics class are homozygous for this gene. Theoretically, how many of the 90 students will fall asleep during the next lecture?

The photos below show flowers from two Arabidopsis plants. The plant on the left is wild-type (unmutated); the other carries a mutation that causes its flowers to have sepals and petals instead of stamens and carpels. The mutation inactivated one of the plant's ABC floral identity genes. Refer to Figure 10.8 and decide which gene (A, B, or C) has been inactivated.

Bruce Ames and his colleagues have pointed out that although detailed toxicological analysis has been conducted on synthetic chemicals, almost no information is available about the mutagenic or carcinogenic effects of the toxins produced by plants as a natural defense against fungi, insects, and animal predators. Tens of thousands of such compounds have been discovered, and he estimates that in the United States adults eat about 1.5 g of these compounds each daylevels that are approximately 10,000 times higher than those of the synthetic pesticides present in the diet. For example, cabbage contains 49 natural pesticides and metabolites, and only a few of these have been tested for their carcinogenic and mutagenic effects. a. With the introduction of new foods into the U.S. diet over the last 200 years (mangoes, kiwi fruit, tomatoes, and so forth), has there been enough time for humans to develop resistance to the mutagenic effects of the toxins present in those foods? b. The natural pesticides present in plants constitute more than 99% of the toxins we eat. Should diet planning, especially for vegetarians, take into account the doses of toxins present in the diet?

The gene controlling ABO blood type and the gene underlying nail-patella syndrome are said to show linkage. What does that mean in terms of their relative locations in the genome? What does it mean in terms of how the two traits are inherited with respect to each other?

Figure 9.10 In certain cancers, the GTPase activity of the RAS G-protein is inhibited. This means that the RAS protein can no longer hydrolyze GTP into GDP What effect would this have on downstream cellular events?

INTERPRET DATA Develop a simple hypothesis that would explain the behavior of each of the following types of mutants in E. coli. Mutant a: The map position of this mutation is in the trp operon. The mutant cells are constitutive; that is, they produce all the enzymes coded for by the trp operon, even if large amounts of tryptophan are present in the growth medium. Mutant b: The map position of this mutation is in the trp operon. The mutant cells do not produce any enzymes coded for by the trp operon under any conditions. Mutant c: The map position of this mutation is some distance from the trp operon. The mutant cells are constitutive; that is, they produce all the enzymes coded for by the trp operon, even if the growth medium contains large amounts of tryptophan.