Genetics: Analysis of Genes and Genomes: Keyword Hot Links for chapter 1

James D. Watson once said that he and Francis Crick had no doubt that their proposed DNA structure was essentially correct, because the structure was so beautiful it had to be true! At an internet site accessed by the keyword DNA you can view a large collection of different types of models of DNA structure. Some models highlight the sugar-phosphate backbones, others the A—T and G—C base pairs, still others the helical structure of double-stranded DNA.

How was PKU discovered? The story is told by the Norwegian physician Ivar Følling: "The stage is set in 1934. A mother with two severely mentally retarded children came to see my father. . . . She had asked many doctors for help, which none had been able to give. But this woman was unusually persistent and would not accept the situation without explanation. She had also noticed that a peculiar smell always clung to her children. . . . This woman was advised to seek help from my father [who held a professorship of nutrient research at the University Hospital in Norway]. He of course had no real hope of being able to help her. But he did not want to reject her, and he agreed to examine the children. On clinical examination he found nothing of importance, except the [severe mental retardation], which was beyond doubt. [Urine analysis] was part of his thorough routine examination. On adding ferric chloride [to normal urine] the color normally stays brownish, [but in the case of these children] a deep green color developed. He had not seen this reaction before. . . He concluded that two mentally retarded children excreted a substance not found in normal urine. But which substance?" Consult this keyword site for more information on how Asbjørn Følling finally tracked down the cause of the disease.

With proper dietary control of blood phenylalanine, patients with PKU can develop normally and lead normal lives. When dietary control is relaxed, however, blood phenylalanine returns to high levels. This situation is extremely dangerous for a developing fetus, resulting in high risk of congenital heart disease, small head size, mental retardation, and slow growth. Affected children are said to have maternal PKU. They are affected, not because of their own inability to metabolize phenylalanine, but because of high levels of phenyalanine in their mothers' blood. The risk can be reduced, but not entirely eliminated, if PKU mothers plan their pregnancies and adhere to a strict dietary regimen prior to and during pregnancy. To learn more about this unanticipated consequence of dietary treatment of PKU, log onto the phenylalanine hydroxylase knowledge database at the keyword site.

Perhaps surprisingly, the history of the bacteriophage T2 that figures so prominently in the experiments of Hershey and Chase is clouded in mystery. Indeed, the time, place, and source material for the original isolation of phages T2, T4, and T6 (known as the "T-even phages") may never be known with certainty. Use the keyword T2 to learn what is known about its origin and the sleuthing required to find it out.