Control of Gene Expression

The giant transgenic mouse on the left was produced by injecting a rat gene for growth hormone into a mouse embryo a normal-size mouse is on the right. To ensure expression, the rat gene was linked to a DNA sequence that stimulates the transcription of mouse DNA whenever heavy metals are present. Zinc was provided in the food for the transgenic mouse some transgenic mice produced 800 times the normal levels of growth hormone. (Courtesy of Dr. Ralph L. Brinster, School of Veterinary Medicine,...

Analyzing Pedigrees

An important technique used by geneticists to study human inheritance is the pedigree. A pedigree is a pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics. The symbols commonly used in pedigrees are summarized in i Figure 6.2. The pedigree shown in I Figure 6.3a illustrates a family with Waardenburg syndrome, an autosomal dominant type of deafness that may be accompanied by fair skin, a white forelock, and visual...

Chromosome Mutations and Cancer

Most tumors contain cells with chromosome mutations. For many years, geneticists argued about whether these chromosome mutations were the cause or the result of can cer. Some types of tumors are consistently associated with specific chromosome mutations, suggesting that in these cases the specific chromosome mutation played a pivotal role in the development of the cancer. However, many cancers are not associated with specific types of chromosome abnormalities, and individual gene mutations are...

Rna

I 8.34 The process of reproduction differs in positive-strand RNA viruses and negative-strand RNA viruses. RNA viruses capable of integrating into the genome of their hosts, much as temperate phages insert themselves into bacterial chromosomes, are called retroviruses (FIGURE 8.35a). Because the retroviral genome is RNA, whereas that of the host is DNA, a retrovirus must produce reverse transcriptase, an enzyme that synthesizes complementary DNA (cDNA) from either an RNA or a DNA template. A...

The Genetic Legacy of Chernobyl

Early on the morning of April 26, 1986, unit 4 of the Chernobyl nuclear power plant in northern Ukraine exploded, creating the worst nuclear disaster in history. The explosion blew off the 2000-ton metal plate that sealed the top of the reactor and ignited hundreds of tons of graphite, which burned uncontrollably for 10 days. The exact amount of radiation released in the explosion and ensuing fire is still unknown, but a minimum estimate is 100 mil lion curies, equal to a medium-sized nuclear...

Positive Control and Catabolite Repression

E. coli and many other bacteria will metabolize glucose preferentially in the presence of lactose and other sugars. They do so because glucose enters glycolysis without further modification and therefore requires less energy to metabolize than do other sugars. When glucose is available, genes that participate in the metabolism of other sugars are repressed, in a phenomenon known as catabolite repression. For example, the efficient transcription of the lac operon takes place only if lactose is...

Adoption Studies

A third technique that geneticists use to analyze human inheritance is the study of adopted people. This approach is one of the most powerful for distinguishing the effects of genes and environment on characteristics. For a variety of reasons, many children each year are separated from their biological parents soon after birth and adopted by adults with whom they have no genetic relationship. These adopted persons have no more genes in common with their adoptive parents than do two randomly...

The Posttranslational Modifications of Proteins

After translation, proteins in both prokaryotic and eukaryotic cells may undergo alterations termed posttranslational modifications. A number of different types of modifications are possible. As mentioned earlier, the formyl group or the entire methionine residue may be removed from the amino end of a protein. Some proteins are synthesized as larger precursor proteins and must be cleaved and trimmed by enzymes before the proteins can become functional. For others, the attachment of...

Adn

Protease, integrase, reverse transcriptase, RNase genes -Delta sequence (334 bp)-(direct repeat) also generate direct repeats at the point of insertion. Retrotransposons include the Ty elements in yeast, the copia elements in Drosophila, and the Alu sequences in humans. Ty elements in yeast Ty (for transposon yeast) elements are a family of common transposable elements found in yeast many yeast cells have 30 copies of Ty elements. These elements are retrotransposons that are about 6300...

Chemically Induced Mutations

Although many mutations arise spontaneously, a number of environmental agents are capable of damaging DNA, including certain chemicals and radiation. Any environmental agent that significantly increases the rate of mutation above the spontaneous rate is called a mutagen. The first discovery of a chemical mutagen was made by Charlotte Auerbach, who was born in Germany to a Jewish family in 1899. After attending university in Berlin and doing research, she spent several years teaching at various...

Function

U1 attaches to 5' end of intron commits intron to splicing no direct role in splicing Positions 5' end of intron near branch point for lariat formation Holds 5' end of intron near branch point Positions 5' end of intron near branch point Anchors first exon to spliceosome subsequent to cleavage juxtaposes two ends of exon for splicing Juxtaposes two ends of exon for splicing Delivers U6 to intron no direct role in splicing between different snRNAs (summarized in Table 14.2). These interactions...

Translational and Posttranslational Control

Ribosomes, aminoacyl tRNAs, initiation factors, and elongation factors are all required for the translation of mRNA molecules. The availability of these components affects the rate of translation and therefore influences gene expression. The initiation of translation in some mRNAs is regulated by proteins that bind to the mRNA's 5' UTR and inhibit the binding of ribosomes, similar to the way in which repressor proteins bind to operators and prevent the transcription of structural genes. Many...

Environmental Sex Determination

Genes have had a role in all of the examples of sex determination discussed thus far, but sex is determined fully or in part by environmental factors in a number of organisms. One fascinating example of environmental sex determination is seen in the marine mollusk Crepidula fornicata, also known as the common slipper limpet ( FIGURE 4.8). Slipper limpets live in stacks, one on top of another. Each limpet begins life as a swimming larva. The first larva to settle on a solid, unoccupied substrate...

Other Types of DNA Repair

The DNA repair pathways described so far respond to damage that is limited to one strand of a DNA molecule, leaving the other strand to be used as a template for the synthesis of new DNA during the repair process. Some types of DNA damage, however, affect both strands of the molecule and therefore pose a more severe challenge to the DNA repair machinery. Ionizing radiation frequently results in doublestrand breaks in DNA. The repair of double-strand breaks is frequently by homologous...

The Limitations of Heritability

Knowledge of heritability has great practical value, because it allows us to statistically predict the phenotypes of offspring on the basis of their parent's phenotype. It also provides useful information about how characteristics will respond to selection (see next section). In spite of its importance, heritability is frequently misunderstood. Heritability does not provide information about an individual's genes or the environmental factors that control the development of a characteristic, and...

General Principles of Gene Regulation

One of the major themes of molecular genetics is the central dogma, which stated that genetic information flows from DNA to RNA to proteins (see Figure 10.17a) and provided a molecular basis for the connection between genotype and phenotype. Although the central dogma brought coherence to early research in molecular genetics, it failed to address a critical issue How is the flow of information along the molecular pathway regulated Consider E. coli, a bacterium that resides in your large...

Agricultural Products

Recombinant DNA technology has had a major effect on agriculture, where it is now used to create crop plants and domestic animals with valuable traits. For many years, plant pathologists had recognized that plants infected with mild strains of viruses are resistant to infection by virulent strains. Using this knowledge, geneticists have created viral resistance in plants by transferring genes for viral proteins to the plant cells. A genetically engineered squash, called Freedom II, carries...

Estimating Allelic Frequencies with the Hardy Weinberg

A practical use of the Hardy-Weinberg law is that it allows us to calculate allelic frequencies when dominance is present. For example, cystic fibrosis is an autosomal recessive disorder characterized by respiratory infections, incomplete digestion, and abnormal sweating (see p. 000 in Chapter 6). Among North American Caucasians, the incidence of the disease is approximately 1 person in 2000. The formula for calculating allelic frequency (Equation 23.3) requires that we know the numbers of...

Genetic Counseling and Genetic Testing

Our knowledge of human genetic diseases and disorders has expanded rapidly in the past 20 years. Victor McKusick's Mendelian Inheritance in Man now lists more than 13,000 human genetic diseases, disorders, and traits that have a simple genetic basis. Research has provided a great deal of information about the inheritance, chromosomal location, biochemical basis, and symptoms of many of these genetic traits. This information is often useful to people who have a genetic condition. Genetic...

Mm

Allele A is epistatic to allele B. Indicate whether each of the following statements is true or false. Explain why. (a) Alleles A and B are at the same locus. (b) Alleles A and B are at different loci. (c) Alleles A and B are always located on the same chromosome. (d) Alleles A and B may be located on different, homologous chromosomes. (e) Alleles A and B may be located on different, nonhomologous chromosomes. * 21. In chickens, comb shape is determined by alleles at two loci (R, r and P,...

Connecting Concepts Across Chapters 9

This chapter has focused on three specialized but important topics the genetics of development, the immune system, and cancer. In addition to their relevance to genetics, these topics have obvious medical importance and all are the subject of intense research. The results of early experiments demonstrated that genes are not usually lost or permanently altered in the course of development rather, development proceeds through the regulation of gene expression. The basic question for development...

Info

Describe some of the ways in which your own genetic makeup affects you as a person. Be as specific as you can. Pick one of the following ethical or social issues and give your opinion on this issue. For background information, you might read one of the articles on ethics listed and marked with an asterisk in Suggested Readings at the end of this chapter. (a) Should a person's genetic makeup be used in determining his or her eligibility for life insurance (b) Should biotechnology companies be...

The Nature of Cancer

Normal cells grow, divide, mature, and die in response to a complex set of internal and external signals. A normal cell receives both stimulatory and inhibitory signals, and its growth and division are regulated by a delicate balance between these opposing forces. In a cancer cell, one or more of the signals has been disrupted, which causes the cell to proliferate at an abnormally high rate. As they lose their response to the normal controls, cancer cells gradually lose their regular shape and...

Techniques for the Study of Bacteriophages

Viruses reproduce only within host cells so bacteriophages must be cultured in bacterial cells. To do so, phages and bacteria are mixed together and plated on solid medium in a petri plate. A high concentration of bacteria is used so that the colonies grow into one another and produce a continuous layer of bacteria, or lawn, on the agar. An individual phage infects a single bacterial cell and goes through its lytic cycle. Many new phages are released from the lysed cell and infect additional...

Application Questions And Problems

In cucumbers, orange fruit color (R) is dominant over cream fruit color (r). A cucumber plant homozygous for orange fruits is crossed with a plant homozygous for cream fruits. The F1 are intercrossed to produce the F2. (a) Give the genotypes and phenotypes of the parents, the F1, and the F2. (b) Give the genotypes and phenotypes of the offspring of a backcross between the F1 and the orange parent. (c) Give the genotypes and phenotypes of a backcross between the F1 and the cream parent....

Uej

Identity of individual segments defined 121.12 A cascade of gene regulation establishes the polarity and identity of individual segments of Drosophila. In development, successively smaller regions of the embryo are determined. Programmed Cell Death in Development Cell death is an integral part of multicellular life. Cells in many tissues have a limited life span, and they die and are replaced continually by new cells. Cell death shapes many body parts during development it is responsible for...

Genetic Variation

An obvious and pervasive feature of life is variability. Consider a group of students in a typical college class, the members of which vary in eye color, hair color, skin pigmentation, height, weight, facial features, blood type, and susceptibility to numerous diseases and disorders. No two students in the class are likely to be even remotely similar in appearance (< Figure 23.2a). Humans are not unique in their extensive variability almost all organisms exhibit variation in phenotype. For...

Lesch Nyhan Syndrome and the Relation Between Genotype and Phenotype

William Nyhan and his student Michael Lesch examined a seriously ill boy with a strange combination of symptoms. The boy had blood in his urine, high concentrations of uric acid in his blood, and uncontrollable spasms in his arms and legs. He was mentally retarded and self-destructively bit his fingers and lips. After carefully studying the boy, Nyhan and Lesch came to the conclusion that he was afflicted by an undescribed disease. Soon other patients with similar symptoms were...

The Study of Human Genetic Characteristics

Humans are the best and the worst of all organisms for genetic study. On the one hand, we know more about human anatomy, physiology, and biochemistry than we know about most other organisms for many families, we have detailed records extending back many generations and the medical implications of genetic knowledge of humans provide tremendous incentive for genetic studies. On the other hand, the study of human genetic characteristics presents some major obstacles. First, controlled matings are...

Radiation Exposure in Humans

People are routinely exposed to low levels of radiation from cosmic, medical, and environmental sources, but there have also been tragic events that produced exposures of much higher degree. Any chemical that significantly increases the number 17.26 Hiroshima was destroyed by an atomic bomb on August 6, 1945. The atomic explosion produced many somatic mutations among the survivors. (Stanley Troutman AP.) 17.26 Hiroshima was destroyed by an atomic bomb on August 6, 1945. The atomic explosion...

The Genetic History of Tristan da Cuna

In the fall of 1993, geneticist Noe Zamel arrived at Tristan da Cuna, a small remote island in the South Atlantic (< Figure 23.1). It had taken Zamel 9 days to make the trip from his home in Canada, first by plane from Toronto to South Africa and then aboard a small research vessel to the island. Because of its remote location, the people of Tristan da Cuna call their home the loneliest island, but isolation was not what attracted Zamel to Tristan da Cuna. Zamel was looking for a gene that...

Molecular Evolution of HIV in a Florida Dental Practice

Center for Disease Control (CDC) reported that a young woman in Florida (later identified as Kimberly Bergalis) had become HIV positive after undergoing an invasive dental procedure performed by a dentist who had AIDS. Bergalis had no known risk factors for HIV infection and no known contact with other HIV-positive persons. The CDC acknowledged that Bergalis might have acquired the infection from her dentist. Subsequently, the dentist wrote to all of his patients,...

I

1.2 Genes influence susceptibility to many diseases and disorders. (a) X-ray of the hand of a person suffering from diastrophic dysplasia (bottom), a hereditary growth disorder that results in curved bones, short limbs, and hand deformities, compared with an X-ray of a normal hand (top). (b) This disorder is due to a defect in a gene on chromosome 5. Other genetic disorders encoded by genes on chromosome 5 also are indicated by braces. (Part a top, Biophoto Associates Science Source Photo...

Challenge Questions

Dwarfism is a recessive trait in Hereford cattle. A rancher in western Texas discovers that several of the calves in his herd are dwarfs, and he wants to eliminate this undesirable trait from the herd as rapidly as possible. Suppose that the rancher hires you as a genetic consultant to advise him on how to breed the dwarfism trait out of the herd. What crosses would you advise the rancher to conduct to ensure that the allele causing dwarfism is eliminated from 36. A geneticist discovers an...

Creating Giant Mice Through Gene Regulation

In 1982, a group of molecular geneticists led by Richard Palmiter at the University of Washington produced gigantic mice that grew to almost twice the size of normal mice. Palmiter and his colleagues created these large mice through genetic engineering, by injecting the rat gene for growth hormone into the nuclei of fertilized mouse embryos and then implanting these embryos into surrogate mouse mothers. In a few embryos, the rat gene became incorporated into the mouse chromosome and, after...

Pattern Baldness In 3 Generatiins Of Addams Family

Puberty Hen

I 5.12 Pattern baldness is a sex-influenced trait. This trait is seen in three generations of the Adams family (a) John Adams (1735-1826), the second president of the United States, was father to (b) John Quincy Adams (1767-1848), who was father to (c) Charles Francis Adams (1807-1886). Pattern baldness results from an autosomal gene that is thought to be dominant in males and recessive in females. (Part (a) National Museum of American Art, Washington, D.C. Art Resource, NY (b) National...

Ctn

(a) Draw the pairing arrangement of these chromosomes in prophase I of meiosis. (b) Diagram the alternate, adjacent-1, and adjacent-2 segregation patterns in anaphase I of meiosis. (c) Give the products that result from alternate, adjacent-1, and adjacent-2 segregation. 30. Red-green color blindness is a human X-linked recessive disorder. A young man with a 47,XXY karyotype (Klinefelter syndrome) is color-blind. His 46,XY brother also is colorblind. Both parents have normal color vision. Where...

To How Many Cistrons Do These Mutations Belong

(a) To how many functional genes (cistrons) do these mutations belong (b) Which mutations belong to the same functional gene 31. As a summer project, a microbiology student independently isolates two mutations in E. coli that are auxotrophic for glycine (gly-). The student wants to know whether these two mutants occur at the same cistron. Outline a procedure that the student could use to determine whether these two gly-mutations occur within the same cistron. 32. A group of genetics students...

Pfi4

A plant breeder wants to isolate mutants in tomatoes that are defective in DNA repair. However, this breeder does not have the expertise or equipment to study enzymes in DNA repair systems. How could the breeder identify tomato plants that are deficient in DNA repair What are the traits to look for 31. A genetics instructor designs a laboratory experiment to study the effects of UV radiation on mutation in bacteria. In the experiment, the students expose bacteria plated on petri plates to...

Introduction to Genetics

The Role of Genetics in Biology Genetic Variation is the Foundation of Evolution Divisions of Genetics Early Written Records The Rise of Modern Genetics Twentieth-Century Genetics The Future of Genetics Basic Concepts in Genetics Alexis, heir to the Russian throne, and his father Tsar Nicholas Romanoff II. Hulton Archive by Getty Images. Alexis, heir to the Russian throne, and his father Tsar Nicholas Romanoff II. Hulton Archive by Getty Images. On August 12, 1904, Tsar Nicholas Romanov II of...

The Complex Genetics of Coat Color in Dogs

Coat color in dogs is an excellent example of how complex interactions between genes may take part in the determination of a phenotype. Domestic dogs come in an amazing variety of shapes, sizes, and colors. For thousands of years, humans have been breeding dogs for particular traits, producing the large number of types that we see today. Each breed of dog carries a selection of genes from the ancestral dog gene pool these genes define the features of a particular breed. One of the most obvious...

Natural Gene Transfer and Antibiotic Resistance

Many pathogenic bacteria have developed resistance to antibiotics, particularly in environments where antibiotics are routinely used, such as hospitals and fish farms. Massive amounts of antibiotics are often used in aquaculture to prevent infection in the fish and enhance their growth. The continual presence of antibiotics in these environments selects for resistant bacteria, which reduces the effectiveness of antibiotic treatment for medically important infections. Antibiotic resistance in...

The Inheritance of Continuous Characteristics

So far, we've dealt primarily with characteristics that have only a few distinct phenotypes. In Mendel's peas, for example, the seeds were either smooth or wrinkled, yellow or green the coats of dogs were black, brown, or yellow blood types were of four distinct types, A, B, AB, or O. Characteristics such as these, which have a few easily distinguished phenotypes, are called discontinuous characteristics. Not all characteristics exhibit discontinuous pheno-types. Human height is an example of...

Humansexdetermination

Klinefelter Syndrome Characteristics

4.10 Persons with Turner syndrome have a single X chromosome in their cells. a Characteristic physical features. b Chromosomes from a person with Turner syndrome. Part a, courtesy of Dr. Daniel C. Postellon, Devos Children's Hospital Part b, Dept. of Clinical Cytogenics, Addenbrookes Hospital Science Photo Library Photo Reseachers. secondary sex characteristics remain immature menstruation is usually absent, breast development is slight, and pubic hair is sparse. This syndrome is seen in 1 of...