Chapter Seven
ANSWERS TO REVIEW QUESTIONS
1. Individual genes that contribute to multifactorial traits follow Mendel’s laws. Their effects are
additive, but not necessarily evenly so.
2. Severity of cystic fibrosis reflects regularity of postural drainage exercises, drugs taken, and
the infections to which an individual is exposed.
3. A Mendelian multifactorial trait is caused by one gene and environmental influences; a
polygenic multifactorial trait is caused by more than one gene and the environment.
4. No
5. The bell curve means that genotypes with many heterozygotes are more common than
genotypes with more homozygotes—irrespective of the trait.
6. Heritability for skin color changes because duration and intensity of sun exposure changes.
7. The twins are DZ and so they inherited different combinations of the parents’ genes that
affect skin color.
8. More genotypes including many heterozygous genes specify medium brown than more
extreme colors.
9. Eye color has a greater heritability because the environment has a greater influence on
height than on eye color.
10. a. Empiric risk is based on observations of trait prevalence in a particular
population or group of individuals.
b. Twin studies approximate the degree of heritability by comparing trait prevalence among
pairs of MZ twins to DZ twins. The greater the difference, the higher the heritability.
c. Inherited traits may stand out in an adoptee’s family where each member lives in the
same environment, but the adopted individual has different genes.
d. GWASs establish correlations between particular gene variants or sections of
chromosomes (haplotypes) and inheritance of certain traits or susceptibilities.
11. Cardiovascular functioning: apolipoproteins, lipoprotein lipase, and fibrinogen. Body weight:
leptin, neuropeptide Y, and ghrelin.
12. A GWAS indicates an association, it does not demonstrate causation and so actual gene
annotation is necessary to assign a specific gene to a specific trait or illness.
13. Genome sequencing will identify the genes that GWASs only point to.
ANSWERS TO APPLIED QUESTIONS
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1. Heritability is not the degree to which a trait is inherited. It is the degree to which heredity
contributes to the variability of a trait.
2. Race (skin color) is not the most accurate way to predict drug response. Genes that control
metabolism of the drug are.
3. A genetic change in a population would not occur in so short a time. Therefore, the cause for
the increase in obesity is largely environmental, perhaps acting on inherited susceptibilities.
4. The heritability, 0.54, suggests about equal influence of genes and the environment.
5. Several narrow, plus few genes with greater effect is broad.
6. Compare SNP patterns between 500 people who have restless leg syndrome (RLS) and
500 people who do not using a case-control design. Each individual in the RLS group is
matched with an individual in the control group who shares as many characteristics as
possible, including age, sex, activity level, and environmental exposures.
7. GWAS in people with early negative experiences compared to unaffected controls.
8. In most cases of age-related macular degeneration, no single gene exerts a powerful
causative effect.
9. It would be important to test the drug on people whose high LDL is not due to controllable
environmental risk factors, such as poor diet.
10. Pulmonary fibrosis is considered a disease of aging because the environmental causes—
viral infections and exposure to inhaled irritants—accumulate with time.
11. Alter the microbiome to resemble what it becomes following weight loss surgery.
ANSWERS TO WEB ACTIVITIES
1. Mutations in p53 impair DNA repair. Mutations in TERT disrupt telomere shortening.
Mutations in IL1A and IL1B affect the immune response, which may allow cancer cells to
persist. Mutations in CYP1A1 affects cell division rate. Mutations in EPHX1 affect
detoxification of oxidants. Mutations in CRR9 block apoptosis.
2. Protein content of cow milk http://pubs.ext.vt.edu/404/404-084/404-084_pdf.pdfAnswers;
Beef tenderness http://extension.missouri.edu/p/G2910; Grain yield per wheat plant
http://www.ccsenet.org/journal/index.php/jas/article/view/12163
3. Injuries, violence, and infections have low heritabilities. Certain congenital anomalies, heart
diseases, and cancers would have higher heritabilities.
4. Apolipoprotein E transports cholesterol. The LDL receptor is a cell surface protein that
regulates endocytosis of LDL. Apolipoprotein A’s exact function is unknown but may be
involved in clotting. Angiotensinogen regulates blood pressure. Beta-2 adrenergic receptor
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without the prior written consent of McGraw-Hill Education.
dilates blood vessels, improving circulation. Toll-like receptor 4 controls immune system
response to certain bacterial infections. C-reactive protein controls inflammation.
5. Eating disorders do not have a large genetic component.
ANSWERS TO CASE STUDIES AND RESEARCH RESULTS
1. The experimental results support that Parkinson disease is largely caused by environmental
factors. Good news, because exposure to toxins is controllable.
2. This study is poorly done because the characteristics are self-reported and therefore
subjective. In addition, close relatives share environments as well as genes. The study was
therefore flawed, and heritability indicates that genes exert a greater influence than
environmental factors—not that genes cause a life of crime.
3. The findings can be used to identify patients whose heart health might benefit from their
taking anti-inflammatory drugs.
4. ACE controls blood pressure and the kidneys’ handling of salt. Many people regard genetic
testing to choose a child’s sport as a bad idea. Certain genotypes are associated with
endurance during extreme sports, such as mountaineering.
5. No. Concordance for DZ twins is very low, so the genetic contribution to anorexia is small.
6. GWAS
7. Researchers search for SNPs that most siblings with schizophrenia share but siblings who
do not both have the condition do not share. These genomic regions may contain genes that
contribute to schizophrenia.
8. The BMI indicates a genetic component to body weight, but the fact that exercise reduced
BMI indicates an environmental component too. It would be important to test the same
people before and after exercise intervention to separate nature from nurture.
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without the prior written consent of McGraw-Hill Education.