Chapter 5 genetics practice problems

Which statement best describes a multifactorial disease compared with a nuclear single-gene Mendelian disorder?

B. It results from multiple genetic factors and environmental influences. Multifactorial diseases involve multiple genes and environmental influences, making their inheritance more complex.

A researcher finds that a disease occurs more frequently among the biological relatives of affected individuals than in the general population. Which conclusion is best supported by this observation alone?

D. Inherited factors may contribute to disease susceptibility. Greater disease frequency among biological relatives is consistent with a genetic contribution, although it does not prove genetics is the only cause.

A condition has a prevalence of 2% in the general population and 6% among siblings of affected individuals. Using the relative risk ratio (λr), what is the value?

C. 3. λr = prevalence among relatives / prevalence in the general population = 6% / 2% = 3.

The relative risk ratio for a disease is λr = 1. Which interpretation is correct?

A. Relatives have the same disease likelihood as the general population. A ratio of 1 indicates no increased disease likelihood among relatives compared with the general population.

A researcher wants to estimate the proportion of variation in a trait attributable to genetic factors within a particular population and environment. Which concept is most appropriate?

B. Heritability. Heritability estimates the proportion of trait variance attributable to genetic factors in a population and specific environment.

Which approach compares disease occurrence in monozygotic (MZ) and dizygotic (DZ) twins to help distinguish genetic from environmental influences?

C. Twin study. Twin studies compare genetically related groups with different degrees of genetic similarity to help investigate genetic and environmental contributions.

A trait such as height varies across a continuous range, and alleles at multiple loci make additive contributions to that variation. Which concept best explains this pattern?

A. Polygenic theory of quantitative traits. Polygenic theory explains continuous variation through additive contributions from alleles at multiple loci.

A genetic researcher investigates a common disease by testing statistical associations between genetic variants and disease status across the population. Which method is most directly suited to this goal?

D. Genomewide association study (GWAS). GWAS identifies statistical associations between genetic markers and traits across a population.

Which statement correctly describes the common disease-rare variant hypothesis?

B. Multiple rare DNA sequence variants with relatively high penetrance are major contributors. The hypothesis proposes that multiple rare variants, each with relatively high penetrance, contribute to susceptibility.

A family has one child with an isolated multifactorial congenital malformation. Several close relatives are also affected. How does this affect recurrence-risk assessment?

C. The recurrence risk is higher when more family members are affected. The lecture lists multiple affected family members as a factor associated with increased recurrence risk.

A child has a multifactorial disorder that is expressed more severely than in other affected family members. What does the lecture predict about recurrence risk?

A. It is higher when the proband's disease expression is more severe. The lecture lists greater severity of disease expression in the proband as a factor associated with higher recurrence risk.

A researcher finds a disease occurs more frequently among biological relatives of affected individuals than among their spouses. Which approach is being applied?

B. Comparing disease relative risk in biological relatives with biologically unrelated family members. Comparing biological relatives with unrelated family members, such as spouses or adoptees, can help distinguish genetic from environmental influences.

True or false: Heritability describes an individual person's probability of developing a disease and remains the same regardless of environment.

False. Heritability describes the proportion of trait variance attributable to genetic factors in a population and a specific environment, not an individual's disease probability.

True or false: In multifactorial disease, recurrence risk usually decreases rapidly among relatives who are more distantly related to the affected person.

True. Recurrence risk generally decreases as relatives become more distantly related.

Which findings or principles are associated with multifactorial diseases? Select all that apply: (A) They commonly involve genetic and environmental factors. (B) They always show a clear Mendelian inheritance pattern. (C) Recurrence risk is higher when more than one family member is affected. (D) Recurrence risk usually increases in more distantly related relatives.

A and C. Multifactorial diseases commonly involve genetic and environmental factors, and recurrence risk is higher when more than one family member is affected.

A researcher studies blood pressure, which varies across a continuous range in a population. Which type of trait is being examined? A. Qualitative trait; B. Quantitative trait; C. Chromosomal trait; D. Mitochondrial trait

B. Quantitative trait. Explanation: Quantitative traits can be measured numerically and often show continuous variation.

Two individuals carry different genetic variants that may contribute to the same common disease. Which research approach is most consistent with investigating genetic contributions across many individuals? A. Genome-wide association study; B. Single-family pedigree review only; C. Environmental exposure survey only; D. Chromosome count in one individual

A. Genome-wide association study (GWAS). Explanation: A GWAS examines associations between genetic variants and a trait or disease across a population.

True or False: A familial pattern of disease is sufficient by itself to prove that the disease is caused entirely by genetic factors.

False. Explanation: Familial clustering can reflect genetic influences, shared environments, or both, so it does not prove that genetics alone causes the disease.

Which description best fits the liability-threshold model of a multifactorial disease? A. Disease occurs whenever one specific disease allele is inherited; B. Disease occurs when an underlying combined liability exceeds a threshold; C. Disease occurs only after an environmental exposure, regardless of genetics; D. Disease occurs only when chromosome number changes

B. Disease occurs when an underlying combined liability exceeds a threshold. Explanation: Combined genetic and environmental influences create liability, with disease occurring when liability crosses a threshold.

Which intervention can reduce the risk of neural tube defects? A. Folic acid supplementation; B. Avoiding all inherited genetic variants; C. Increasing chromosome number; D. Eliminating all variation in the population

A. Folic acid supplementation. Explanation: Folic acid supplementation before and during early pregnancy reduces the risk of neural tube defects.

Which statement best describes a qualitative trait in contrast with a quantitative trait? A. It is typically recorded in distinct categories; B. It must be caused by environmental factors alone; C. It always follows mitochondrial inheritance; D. It always has a continuous distribution

A. It is typically recorded in distinct categories. Explanation: Qualitative traits are generally classified into categories rather than expressed as continuous numerical measurements.

Select all that apply: Which statements are consistent with the multifactorial model of common disease? A. More than one genetic factor may contribute; B. Environmental influences may contribute to disease risk; C. Every affected person must have the same single causal mutation; D. People with similar genetic susceptibility may have different outcomes

A, B, and D. Explanation: Multifactorial diseases can involve multiple genes and environmental influences, and people with similar susceptibility may have different outcomes.

Which example most clearly represents a somatic genetic change rather than a typical inherited germline change? A. A genetic change acquired in a body cell during life; B. A variant present in an egg or sperm that is passed to a child; C. A chromosome variant inherited from a parent; D. A genetic variant present in the family across generations

Correct answer: A. A genetic change acquired in a body cell during life. Explanation: Somatic changes arise in body cells and are not typically passed to offspring.

9. Which hypothesis proposes that common diseases may involve many common genetic variants, each contributing a small effect? A. Common disease–common variant hypothesis; B. Common disease–rare variant hypothesis; C. Single-gene dominant hypothesis; D. Chromosomal nondisjunction hypothesis

Correct answer: A. Common disease–common variant hypothesis. Explanation: This hypothesis proposes that common variants may contribute to susceptibility to common diseases.

10. True or False: Heritability is a fixed value that must remain the same across all populations and environments.

Correct answer: False. Explanation: Heritability depends on the genetic and environmental variation present in the population and environment being studied.

11. A condition is classified as multifactorial. Which additional finding would be most compatible with that classification? A. Risk reflects a combination of genetic susceptibility and environmental influences; B. The condition can only be caused by a single chromosome deletion; C. The condition must be inherited in a fixed dominant pattern; D. Environmental factors cannot change the likelihood of disease

Correct answer: A. Risk reflects a combination of genetic susceptibility and environmental influences. Explanation: Multifactorial conditions result from combined genetic and environmental influences.

12. Which research design can help investigate inherited factors and shared family environments by comparing adopted individuals with biological and adoptive relatives? A. Adoption study; B. A study of unrelated individuals only; C. A chromosome count study; D. A study measuring one person's blood pressure once

Correct answer: A. Adoption study. Explanation: Adoption studies can help distinguish genetic relationships from aspects of the rearing environment.

13. Why can recurrence-risk estimates for multifactorial diseases be useful even when they cannot predict an individual's outcome with certainty? A. They establish that every relative will develop the disease; B. They identify the exact causal variant in every family; C. They describe probabilities based on patterns observed in groups and families; D. They eliminate the influence of environmental exposures

Correct answer: C. They describe probabilities based on patterns observed in groups and families. Explanation: Recurrence-risk estimates provide probabilistic guidance rather than certainty about an individual's outcome.

14. What does a quantitative trait locus (QTL) refer to? A. A genomic region associated with variation in a quantitative trait; B. A location that always causes a single chromosomal syndrome; C. A region that measures environmental exposure without genetic information; D. A specific gene that must fully determine the trait

Correct answer: A. A genomic region associated with variation in a quantitative trait. Explanation: A QTL is a genomic region associated with variation in a measurable trait.

15. Which example best illustrates the difference between association and proof of causation in complex-disease research? A. A genetic variant is statistically associated with disease, but further evidence is needed to establish its causal role; B. A disease-associated variant is automatically proven to be the only cause of disease; C. A variant is found in one person, so it must explain population-wide disease risk; D. A disease has environmental influences, so genetic associations cannot exist

Correct answer: A. A genetic variant is statistically associated with disease, but further evidence is needed to establish its causal role. Explanation: A statistical association identifies a relationship but does not by itself prove causation.