ANSWERS TO REVIEW QUESTIONS
CHAPTER 7
1. Individual genes may follow Mendel’s laws. However, gene products (proteins) may interact
with each other and with environmental factors.
2. Sickle cell disease and cystic fibrosis are single gene traits. Hypertension is polygenic and
multifactorial.
3. A Mendelian multifactorial trait is caused by one gene and environmental influences, whereas
a polygenic multifactorial trait is caused by more than one gene and environmental
influences.
4.
Heritability for skin color changes because the duration and intensity of sun exposure
contribute to skin color.
5.
Skin color is controlled by many different genes and interaction with the environment. The
twins in figure 7.4 obviously inherited different combinations of their parent’s genes that affect
skin color.
6.
More genotypes specify a medium brown skin color than specify other colors.
7.
The Connecticut study compared the height of two groups of students from different decades,
inferring the effect of environmental influences such as diet and health on phenotype. The
Finland study is a longitudinal, genome-wide association study looking for genes associated
with height at different ages in a cohort born in 1966. The Connecticut study compared
different groups and didn’t follow genes. The Finland study followed the same individuals and
did consider genetic information.
8.
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. GWAS identify patterns of genetic variability that are seen much more often among
people who share a specific trait or medical condition.
9. Eye color has a greater heritability because the environment has a greater influence on height
than on eye color.
10. Many people must be surveyed to determine whether a certain set of SNPs is exclusively
associated with a particular phenotype. Enough DNA must be considered so that several
SNPs are analyzed, and a case-control strategy must be employed to ensure that the same
SNPs are not found among affected individuals as well as unaffected ones. Finally, if many
SNPs are considered, many combinations must be correlated to phenotypes.
11. New genomic data are used to extend earlier twin and adoptive studies to the population
level.
12. GWAS may point to genes whose functions had not been associated with a particular
phenotype (disease). It considers the entire genome, not just likely candidate genes.
13. Cardiovascular functioning: apolipoproteins, lipoprotein lipase and fibrinogen. Body weight:
leptin, neuropeptide Y, and ghrelin.
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ANSWERS TO APPLIED QUESTIONS
1. Farfel shares 25% with Marbles, 3.125% with Juice, and 12.5% with Angie. The healthiest
kittens would be with Juice because there is the lowest risk of Farfel’s sharing harmful
recessive alleles with him.
2. Familial hypercholesterolemia, CF, PKU
3. Race-based prescribing could eliminate a person in
whom a drug may work, or give a drug to a person in whom
it will not work, or have an adverse effect. Drug effectiveness
does not track with race, but with genotype.
4.
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.
5. The heritability, 0.54, suggests the influence of genes and the environment is about equal.
6. Compare extensive SNP patterns among 500 individuals who have restless legs syndrome
(RLS) and 500 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. Broad
8. Good news because a person could be genetically unlucky, but good news in that there is
plenty of room for environmental intervention.
9. Two groups of genetically identical mouse pups are treated differently – one group is exposed
to extreme stress, and the other lead a peaceful existence. As adults, gene expression is
assessed for the animals, considering genes involved in weight and anxiety. A human study
might compare the incidence of addiction, depression, anxiety, and obesity among people
exposed to extreme stress earlier in life to the incidences among a matched group without early
stress.
ANSWERS TO WEB ACTIVITIES
1. p53 encodes a tumor suppressor protein that when missing disables the body’s ability to
counter smoke-induced damage to DNA. IL1A and IL1B encode interleukins that control the
immune response, which can keep cancer away. CYP1A1 encodes a cytochrome protein that
metabolizes certain components of smoke (carcinogens). EPHX1 encodes expoxide hydrolase,
which breaks down toxins in smoke. TERT encodes a protein that keeps telomeres long so
cancer cells keep dividing. CRR9 enables cells to resist certain cancer drugs.
2. Beef cattle are discussed at http://extension.missouri.edu/p/G2910. Traits are height, fattiness
and tenderness of meat. Dogs are at http://www.italian-greyhound.net/selection.htm Traits are
height, weight, and nervousness. Western wheatgrass is at http://www.jstor.org/pss/4002842.
Traits are spike density, dry matter yield, and vigor.
3. High heritability disorders are cancers, heart disease, and diabetes compared to low
heritability for septicemia, influenza and pneumonia, and accidents. The three higher heritability
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conditions are caused by many genes, and “run in families.” The low heritability conditions have
environmental causes.
4. Apo E transports lipids and breaks down triglycerides. LDL receptor binds the cholesterol
carrier LDL. Apo A transports lipis and is the protein part of HDL. Angiotensinogen controls
blood pressure. Beta-2 adrenergic receptor dilates arteries, increasing blood flow. Toll-like
receptor 4 and C-reactive protein control inflammation.
ANSWERS TO CASE STUDIES AND RESEARCH RESULTS
1. ACE constricts veins. Inhibiting it can treat hypertension, heart failure, and diabetes mellitus
(the ACE inhibitor drugs). Athletes with low blood pressure might have an advantage. The
correlation in the small study described might not apply to Spencer.
2. No. This difference in the concordance between MZ and DZ twins provides evidence of a
genetic component, but Ashley and Maggie are DZ (fraternal) twins.
3.
a. Topography of back of iris intensifies the color, or Tanya inherited dark pigment alleles
from each parent.
b. Different allele combinations
c. Height
d. Height is genetically determined as evidenced by Jamal and Tanya’s above average
height since early childhood. Effect of diet is seen in their greater height compared to the
parents, who did not eat as well.
e. Eye color
4. GWAS
5. Results may identify new drug targets.
6. 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.
7. What other drugs do people in the two populations take? Which diseases are prevalent in one
group but not the other? For each gene, is expression up or down and how does this affect the
metabolism of a specific drug?
8. a. Genes affecting how much is eaten, how calories are metabolized, and how fat is stored in
the body.
b. How the patient population was selected
c. Answers vary depending on student opinion
9. The findings do not support genetic determinism because exercise altered the phenotype.
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