Box 81 continued

Be routinely approved in the United States. However, Dr. Frances Kelsey, newly hired by the FDA, carefully reviewed the application and noted several omissions that prevented her from judging the safety and efficacy of the drug. Merrel Company was eager to start tapping the lucrative U.S. market and, assuming that thalidomide would be approved, had brought in five tons to warehouses in the country. This company had even distributed the drug as an investigational drug to over a thousand doctors,...

IJ 39vv1139Vv

Figure 5.1 Examples ofRestriction Enzyme Sites. The sites are shown whole on the left, and on the right they are shown after being cut by the enzyme. A. Restriction enzyme site for a restriction enzyme from Escherichia coli. B. Restriction enzyme site for a restriction enzyme from Haemophilus influenza. very long stretches of DNA found in cells. Also, since a given restriction enzyme always cuts DNA at the same sequence, these DNA fragments are a collection of pieces that begin and end with the...

Newborn Testing and Conditional Probability

How is the knowledge about the frequency of different genes and genotypes in the population useful As mentioned already, all fifty states test for PKU among their newborns. The accuracy of most of the newborn testing is better than 99.9 percent. Thus, these tests are very accurate but not perfect. Because the tests are accurate, we expect that any baby born with the disease will be detected. However, there is a 0.1 percent chance that even if a baby does not have the disease it will test...

Producing Human Proteins in E Coli

Once the above operations are finished, it is necessary to make many copies of the pieces of recombinant DNA. Copying uses the natural copying mechanism of live bacteria by introducing the recombinant DNA molecule that was made in the test tube into bacterial cells, generally Escherichia coli (E. coli). When treated with appropriate chemicals, Figure 5.3 Making Human Insulin Using Recombinant DNA. A. Partial amino acid sequence of human insulin. B. The DNA sequence corresponding to the amino...

A x a

Figure 2.2 Cross Between Red and White Campion Flowers. The cross-pollination of a red campion with a white campion is depicted at the top. De Vries obtained all red campions from this cross. Then, he self-fertilized, or self-pollinated, these red campions with their own pollen. From this cross, shown below, he observed 25 percent white and 75 percent red campions. and 25 percent of the other type a 3 to 1 ratio. From these and other results of his experiments, using a number of different...

Discovering Disease Genes in Humans

One of the goals of the Human Genome Project is to determine which genes make us prone to disease. This does not mean the types of genetic diseases that are well understood (such as PKU and others) that we described in chapter 3. Rather, we are referring to genes that make some of us more susceptible to certain diseases, such as bacterial infection, high blood pressure, and cancer. These diseases and many others involve many genes as well as environmental factors. Now that the human genome has...

Errors in Chromosome Number

We are all products of a sperm fertilizing an egg. Humans have twenty-two pairs of chromosomes, plus the sex chromosomes. After meiosis, the sperm should have twenty-two chromosomes plus either the X or Y chromosome, and the egg should have twenty-two chromosomes plus an X chromosome (see figure 7.1). But sometimes, errors occur in the process of meiosis, and a given gamete is either missing a chromosome or has more than one copy of a particular chromosome. . When this happens, and the egg or...

Quantitative Traits in Medicine and Agriculture

We saw in chapter 9 that susceptibility to disease is likely to be determined by defects in many genes. Autism seems to belong to that category of diseases. Autism is a neurodevelopmental disorder first recognized as a disease in 1943. It is already apparent during the first three years of life, expressed in lack of verbal communication, social responsiveness, and ritualized behavior. Autism affects approximately 1 child in 2,500. Over the years, several theories have been put forth to explain...

Glossary of Terms

Amino acid Building block of protein molecules. Also important components of our diet. Amniotic fluid The liquid surrounding a fetus in its mother's womb enclosed by the amniotic membrane. The amniotic membrane and its contents constitute the amnion. Antibiotic A chemical that inhibits bacterial or fungal proliferation. Antibody A protein molecule synthesized in the cells of the immune system whose role it is to neutralize antigens. Anticodon The portion of a tRNA molecule that recognizes a...

Human Gene Therapy

It may seem undignified to discuss humans in a chapter devoted to genetically modified animals, yet from a purely biological viewpoint, humans are no different than other mammals in regard to science's ability to modify their genetic material. As you know, it is possible to fertilize human eggs with sperm in a laboratory dish and implant the young, dividing embryo into the uterus of the future mother. That mother may or may not be genetically related to the embryo. This technique is called in...

Measuring Variance in Traits and Estimating Heritability

The differing degree of genetic versus environmental contribution to a trait is called heritability. Many Mendelian, or single-gene traits are unaffected by the environment. An extreme example is our blood type, which is unaffected by the environment and thus is 100 percent heritable. For polygenic traits, genetic factors contribute a portion of the trait, and the environment contributes the rest. If we wish to select animals or plants for a given trait, heritability is an important...

Using Restriction Enzymes and Plasmids to Clone a Gene

We will use the example of the insulin gene to explain how gene cloning works (figure 5.3). Insulin was the first protein to have its amino acid sequence deciphered. This is because it is relatively small (see table 4.1). It is also one that is very important medically. Figure 5.3.A shows a part of the amino acid sequence of human insulin. Because we know the genetic code if we know the sequence of amino acids of a protein, we can make a sequence of DNA, a gene, that corresponds to the sequence...

Uses of Genetically Modified Animals

The basic idea in making genetically modified animals is to turn animals into specialized protein factories, much like what was described for bacteria in chapter 5. The product made by this technique that may be furthest along in development is a blood-clotting factor produced in milk. However, some companies are trying to genetically engineer animals to produce useful proteins in their urine. This may seem repulsive, but there are some real advantages in producing compounds that are secreted...

Genetically Modified Nonfood Plants

Not all potential applications of genetic modification of plants concern food plants, however. In this section, we will describe two other potential applications of genetically modified plants phytoremediation and human vaccine production in plants. Phytoremediation is the act of cleaning up polluted soils with plants. As we know, vast stretches of land, worldwide, are heavily polluted with petrochemicals or toxic heavy-metal salts such as mercury and cadmium. It so happens that soil microbes...

Translation

Messenger RNA molecules are an intermediate step in the decoding of genes they must next be translated into protein products. The machinery that translates mRNAs is quite complicated, and it took many years to unravel the mystery of their functioning. Proteins are polymers of twenty different amino acids arranged in a particular sequence. This is true of proteins from viruses to human beings. Hundreds of thousands of different proteins exist in the living world. They differ by the arrangement...

Medically Important Human Proteins Made in E Coli

Human proteins manufactured in E. coli cells include, among others, insulin, erythropoietin, blood-clotting factors, somatotropin, os-teogenic protein, and tPA, or tissue plasminogen activator. Insulin is used to assist individuals who cannot make their own insulin, people suffering from type I diabetes. Erythropoietin is a protein factor that plays a key role in the production of red blood cells. It is used to treat anemia, in particular anemia that may follow cancer chemotherapy. It is also a...

Another Sex Influenced Trait Male Pattern Baldness

A more dramatic example of a sex-influenced trait is male pattern baldness. Because mostly men are affected, one might guess that it is a sex-linked trait. A classic case of male pattern baldness appears in President Adams's family. The second U.S. president, John Adams, and his son John Quincy Adams, the sixth president, as well as the latter's son and grandson, all had male pattern baldness. If this trait was on the X chromosome, as figure 3.2 shows, a father could not pass the trait onto his...

Mutagens

Since mutations occur in the natural process of DNA replication, how shall we define mutagens It would be strange to define the natural replication of DNA as mutagenic. Thus we will define mutagens as factors that increase the rate of mutation over and above that of the spontaneous mutation rate. Two categories of mutagens will be discussed. One is electromagnetic radiation and the other comprises various chemicals. First, let us look at electromagnetic radiation. Electromagnetic radiation...

Natural Selection Determined Skin Color in Humans

Selection can occur on Mendelian, or single-gene, traits, but also on traits determined by many genes, since selection acts on the pheno-type, as we have seen in the case of goats, lions, and four-o'clock plants. An example of a trait determined by many genes is skin color in humans. Natural selection for or against skin pigmentation is well understood and took place tens of thousands of years ago as modern humans left Africa to colonize the rest of the planet. People from tropical areas with...