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...

Xeroderma pigmentosum is a human disease that results from defects in DNA repair

This concept is discussed further in Chapter 21. Among the best studied of the human DNA repair diseases is xeroderma pigmentosum (Figure 17.31), a rare autosomal recessive condition that includes abnormal skin pigmentation and acute sensitivity to sunlight. Persons who have this disease also have a strong predisposition to skin cancer, with an incidence from 1000 to 2000 times that found in unaffected people. Sunlight includes a strong UV component so...

Info

*Percent overweight was determined by comparing each man's actual weight with a standard recommended weight for his height. Source After A. J. Standard, T.T. Foch, and Z. Hrubec, A twin study of human obesity, Journal of the American Medical Association 256(1986) 52. The degree of environmental similarity between monozy-gotic twins and dizygotic twins is assumed to be the same. This assumption may not always be correct, particularly for human behaviors. Because they look alike, identical twins...

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...

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...

Gene Interaction with Epistasis

Sometimes the effect of gene interaction is that one gene masks hides the effect of another gene at a different locus, a phenomenon known as epistasis. This phenomenon is similar to dominance, except that dominance entails the masking of genes at the same locus allelic genes . In epista-sis, the gene that does the masking is called the epistatic gene the gene whose effect is masked is a hypostatic gene. Epistatic genes may be recessive or dominant in their effects. Recessive epistasis Recessive...

Plasmids

Mammalian Cell Antibiotic Kill Curve

In addition to having a chromosome, many bacteria possess plasmids, small, circular DNA molecules FIGURE 8.6 . Some plasmids are present in many copies per cell, whereas others are present in only one or two copies. In general, plas-mids carry genes that are not essential to bacterial function but that may play an important role in the life cycle and growth of their bacterial hosts. Some plasmids promote mating between bacteria others contain genes that kill other bacteria. Of great importance,...

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...

Suggested Readings

Wickner. 1992. Genetics and enzymology of DNA replication in Escherichia coli. Annual Review of Genetics 26 447-477. A detailed review of replication in bacteria. Bell, S. P., R. Kobayashi, and B. Stillman. 1993. Yeast origin recognition complex functions in transcription silencing and DNA replication. Science 262 1844-1849. A research article on the role of eukaryotic origins of replication in replication and transcription. Blow, J. J., and S. Tada. 2000. A new check on...

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

Metafemale

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...