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