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					Chapter 1              Overview of Genetics
ANSWERS TO REVIEW QUESTIONS

1. Gene pool, genome, chromosome, gene, DNA

2. a. An autosome does not carry genes that determine sex. A sex chromosome does.
   b. Genotype is the allele constitution in an individual for a particular gene. Phenotype is the
       physical expression of an allele combination.
   c. DNA is a double-stranded nucleic acid that includes deoxyribose and the nitrogenous
       bases adenine, guanine, cytosine and thymine. DNA carries the genetic information.
       RNA is a single-stranded nucleic acid that includes ribose and the nitrogenous bases
       adenine, guanine, cytosine and uracil. RNA carries out gene expression.
   d. A recessive allele determines phenotype in two copies. A dominant allele determines
       phenotype in one copy.
   e. Absolute risk refers to an individual's personal risk. Relative risk is in comparison to
       another group, and is less precise.
   f. A pedigree is a chart of family relationships and traits. A karyotype is a chart of
       chromosomes.
    g. A gene is a sequence of DNA that encodes a protein. A genome is all the DNA in a cell.

3. Inherited disease differs from other types of diseases in that recurrence risk is predictable
   for particular individuals in families; predictive testing is possible; and different populations
   have different characteristic frequencies of traits or disorders.

4. CF is caused by one malfunctioning gene. Height reflects the actions of several genes and
   environmental influences, such as diet.

5. A mutant is a variant, usually uncommon, but not necessarily harmful.

6. A genetic test can predict symptoms.

ANSWERS TO APPLIED QUESTIONS

1. 16

2. An individual shares more genes with a sibling (1/2) than with a first cousin (1/8).

3. The benefits: more convictions and exonerations would be obtained at the risk of invading
   the privacy of many people. Use of a population database is not foolproof. An adopted
   person might have an identical twin who is a suspect in a crime, and not know it. The
   database would implicate both twins. To be effective, DNA data should not be the only
   evidence considered.

4. Genetic engineering could mean any intentional change to DNA, whereas a transgenic
   organism has DNA from a member of a different species. A transgenic organism is created
   using a type of genetic engineering.

5. Restricting publication of pathogen genome sequences might or might not prevent
   development of bioweapons, but would hamper research. An answer might balance the gains
   possible from microbiological research – such as new vaccines and treatments – against the
   possibility of abuse of that information.


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6. “ATCG” on the <http://gnn.tigr.org/articles/art_gallery.shtml> website depicts James
   Watson’s DNA.

7. Many cartoons state that the genetic code is human and was recently cracked, that
   geneticists are evil or rich or both, and that genetically modified foods are known to be
   dangerous.

8. Oxidative stress profile for skin health and aging; obesity susceptibility profile; osteopenia
   Pro: If you have one, you can change your behavior to lower the risk.
   Con: If you think the problem is genetic, you may stop efforts to follow a healthy lifestyle.
   The tests are SNP based. Treat skin aging before wrinkles appear. Dangers unknown.

9. The wife.

10. More likely than general population: coronary artery disease, kidney cancer, lung cancer,
    and depression. Less likely than general population: addictive behaviors, diabetes.

11. Multiple sclerosis is multifactorial, and because of interacting, multiple causes, precise
    recurrence risks are not possible.

12. a. It is crucial to know what percentage of people with the carpal tunnel gene variant
       actually develop the condition, and whether an individual’s job assignment would
       overwork the wrists.
    b. The test is not scientifically sound because a predisposition indicates increased
       probability of a future event, not an absolute prediction.
    c. Do not compel a person to take a genetic test, such as threatening job loss.


ADDITIONAL QUESTIONS

1. Leishmaniasis is an infection that humans contract from sandflies that transmit the
   microorganism Leishmania braziliensis. The first sign is a skin lesion, followed by facial
   disfiguration. The disease is endemic (very common) in Bolivia, where it is seen more in
   males, younger people, and those who spend the most time in the forest. A genetic
   susceptibility might also influence who becomes infected, as suggested by highly
   susceptible strains of mice. What type of evidence in the Bolivian population, which consists
   of natives and immigrants, might suggest an inherited component to susceptibility to this
   infection?

2. Osteoporosis thins bones in millions of people. A much rarer, inherited condition,
   osteopetrosis, acts oppositely, increasing bone mass. Osteopetrosis does not affect health,
   and is typically discovered on x-rays. Why might studying how osteopetrosis arises be
   useful, even though it doesn't cause symptoms?
3. In acute intermittent porphyria, an environmental factor such as abuse of drugs or alcohol or
   fasting triggers potentially fatal attacks on the nervous system. An abnormal enzyme causes
   the condition. Why is this disorder considered genetic if it only produces symptoms in the
   presence of a specific environmental trigger?

4. Although seizures are usually not inherited, benign infantile familial convulsions run in
   families. How can studying this inherited illness provide information that may help people
   with non-inherited seizures?



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5. Due to inherited differences in the way the body processes cholesterol, some people can
   eat a fatty diet yet have healthy blood serum cholesterol, and others develop dangerously
   high cholesterol levels if they do not eat wisely. Several drugs can lower blood serum
   cholesterol level. Researchers found that people with a certain variant of a gene encoding a
   protein that transports cholesterol into liver cells (cholesteryl ester transfer protein, or CETP)
   are likely to have a cholesterol problem, and are also more likely to benefit from cholesterol-
   lowering drugs than people with different alleles. What information would be important to
   have before undergoing a CETP gene test and possibly taking a cholesterol-lowering drug?

6. In Graves disease, the immune system attacks the thyroid gland, which normally produces
   hormones controlling energy utilization. Siblings of people with Graves disease are 15 times
   as likely to develop the disorder as people whose siblings are unaffected. Women develop
   the condition more often than men, and a high percentage of affected individuals smoke. Do
   you think that Graves disease is caused solely by an abnormal gene, solely by an
   environmental trigger, or might there be another explanation?

ANSWERS TO ADDITIONAL QUESTIONS

1. An inherited susceptibility to leishmaniasis might be at play if blood relatives who are
   separated geographically become sick more often than do people who have in common only
   where they live.

2. Studying osteopetrosis can reveal how healthy bone mass is maintained, which might
   provide insights into osteoporosis, which has an opposite phenotype and is more common.

3. The condition is inherited because presence of a particular genetic variant is necessary for
   symptoms to occur.

4. Studying this rare inherited condition can reveal basic brain mechanisms that may explain
   how more common seizures occur.

5. Important information includes: the risk of cardiovascular disease to an individual; side
   effects of cholesterol-lowering drugs; the role of diet in controlling gene expression; how
   often a particular genetic variant is associated with increased cholesterol level; success of
   drug treatment.

6. Graves disease might be caused by an inherited susceptibility triggered by an environmental
   influence, such as exposure to female sex hormones or cigarette smoke, or the status of the
   immune system.




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