Human Heredity Principles And Issues 11th Edition by Michael Cummings – Test Bank

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True / False

 

1. ​The additive model for polygenic inheritance proposes that the genes controlling a trait are all on one chromosome.

  a. True
  b. False

 

ANSWER:   False
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-4 The Additive Model for Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-4-1 – Distinguish among complex traits, polygenic traits, and multifactorial traits, and describe factors that complicate their analysis.

 

2. ​For threshold traits, the liability for a genetic disorder is distributed among individuals in a bell-shaped curve.

  a. True
  b. False

 

ANSWER:   True
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-3 – Explain how the threshold model and recurrence risk are used to predict phenotypic distributions of complex traits.

 

3. ​Continuous phenotypic variations can be explained by Mendelian inheritance.

  a. True
  b. False

 

ANSWER:   True
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-3 Complex Traits and Variation in Phenotype
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-3-1 – List the distinguishing characteristics of complex traits.

 

4. ​Dizygotic twins originate from two separate fertilization events.

  a. True
  b. False

 

ANSWER:   True
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-2 – Illustrate the biology of monozygotic and dizygotic twins, and list the assumptions scientists make when conducting research on twins.

 

5. ​A measured heritability of 0.7 means that 70% of the phenotypic variation observed is due to genetic differences within the population.

  a. True
  b. False

 

ANSWER:   True
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-6 Heritability Measures the Genetic Contribution to Phenotypic Variation.
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-6-1 – Define genetic and environmental variance, and explain how heritability, as measured by the correlation coefficient, is used to quantify the contribution of each to phenotypic variations of complex traits.

 

6. ​The genes discovered to date account for only about 5-10% of the total variation in adult height.

  a. True
  b. False

 

ANSWER:   True
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-8 Genetics of Height: A Closer Look
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-8-1 – Explain how single nucleotide polymorphisms (SNPs) and haplotypes are used to reveal genetic contributions to complex traits such as height.

 

7. ​The contributions of genes and environmental factors are strictly defined during the study of complex traits.

  a. True
  b. False

 

ANSWER:   False
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-2 Polygenic Traits Are Controlled by Two or More Genes
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-2-2 – Distinguish among complex traits, polygenic traits, and multifactorial traits, and describe factors that complicate their analysis.

 

8. ​Epigenetic modifications affect the nucleotide sequence of the DNA.

  a. True
  b. False

 

ANSWER:   False
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-2 – Explain how epigenetics contributes to changes in gene expression patterns and in turn, varied phenotypes of multifactorial traits.

 

9. ​Phenotypic variation among individuals with the same genotype is known as genetic variance.

  a. True
  b. False

 

ANSWER:   False
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-6 Heritability Measures the Genetic Contribution to Phenotypic Variation
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-6-1 – Define genetic and environmental variance, and explain how heritability, as measured by the correlation coefficient, is used to quantify the contribution of each to phenotypic variations of complex traits.

 

10. ​Heritability studies cannot provide information about the number, location, or identity of genes involved in specific complex traits.

  a. True
  b. False

 

ANSWER:   True
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-4 – Debate the controversial issues surrounding IQ and race.

 

Multiple Choice

 

11. ​The tall and short phenotypes in pea plants are examples of ____.

  a. ​polygenic traits
  b. ​continuous traits
  c. ​multifactorial traits
  d. ​discontinuous traits
  e. ​gene interaction

 

ANSWER:   d
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-2 Polygenic Traits Are Controlled by Two or More Genes
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-2-1 – Differentiate between discontinuous and continuous phenotypic variation and identify the genetic conditions under which each occurs.

 

12. ​One characteristic of continuous variation is that ____.

  a. ​traits are usually quantified by counting
  b. ​only a single gene pair contributes to the phenotype
  c. ​individual genes have a large effect on the phenotype
  d. ​phenotypic expression varies across a wide range
  e. ​it is best analyzed in individuals rather than in populations

 

ANSWER:   d
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-3 Complex Traits and Variation in Phenotype
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-3-1 – List the distinguishing characteristics of complex traits.

 

13. ​During interaction between genes and environment, the phenotype ____.

  a. ​changes the genotype
  b. ​is expressed as discontinuous variation
  c. ​is variable and undergoes continuous change throughout the life of the organism
  d. ​can be quantitatively subdivided into genotypic and environmental components
  e. ​cannot vary

 

ANSWER:   c
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-1 – Apply basic genetic concepts to the interaction between multiple genes and environmental factors in multifactorial traits.

 

14. ​The heritability of a trait is the ____.

  a. ​sum of all phenotypic variation in a population
  b. ​average amount of genetic variation in each individual
  c. ​proportion of phenotypic variation that is caused by different genotypes
  d. ​absolute measurement of genotypic variation in a population
  e. ​proportion of phenotypic variation that is caused by the environment

 

ANSWER:   c
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-6 Heritability Measures the Genetic Contribution to Phenotypic Variation
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-6-1 – Define genetic and environmental variance, and explain how heritability, as measured by the correlation coefficient, is used to quantify the contribution of each to phenotypic variations of complex traits.

 

15. ​A trait with a heritability value of 0.75 indicates that 75% of the phenotypic variability seen in the population is caused by ____ of the population.

  a. ​genetic differences
  b. ​environmental differences
  c. ​concordance
  d. ​epigenetic effects
  e. ​the equal contribution of the genotype and the environment

 

ANSWER:   a
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-6 Heritability Measures the Genetic Contribution to Phenotypic Variation
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-6-1 – Define genetic and environmental variance, and explain how heritability, as measured by the correlation coefficient, is used to quantify the contribution of each to phenotypic variations of complex traits.

 

16. ​According to Wilhelm Stern’s method of measurement, a ten-year-old child who is able to perform the mental tasks of a ten-year-old (but not of an eleven-year old) has an IQ of ____.

  a. ​80
  b. ​90
  c. ​100
  d. ​110
  e. ​120

 

ANSWER:   c
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-3 – Examine how theories about human intelligence have changed from the late eighteenth to the early twenty-first century.

 

17. ​Twins are concordant for a trait when ____.

  a. ​both twins share the trait with at least one parent
  b. ​only identical twins have the trait
  c. ​only fraternal twins have the trait
  d. ​both twins have the trait
  e. ​all of the twins’ siblings have the trait

 

ANSWER:   d
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-3 – Apply the concept of concordance to the study of heritability of complex traits.

 

18. Cleft palate is ____.​

  a. ​controlled only by genetics
  b. ​a continuously distributed trait
  c. ​controlled by a single gene pair
  d. ​only transmitted from father to son
  e. ​explained by the threshold model of complex traits

 

ANSWER:   e
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-3 – Explain how the threshold model and recurrence risk are used to predict phenotypic distributions of complex traits.

 

19. ​Twin, adoption, and family studies show that obesity has a heritability that averages close to ____.

  a. ​0.1
  b. ​0.3
  c. ​0.5
  d. ​0.7
  e. ​0.9

 

ANSWER:   d
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-4 – Describe how geneticists are using twin studies, animal models, and human genome scanning techniques to study the complex trait of obesity.

 

20. ​Most evidence indicates that skin color is controlled by ____ gene pair(s).

  a. ​one
  b. ​two to three
  c. ​ten
  d. ​five to seven
  e. ​fifteen

 

ANSWER:   c
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-2 – Explain how the study of black-white marriages in the early 1900s determined that human skin color is a complex trait.

 

21. ​Genetic testing for complex traits ____.

  a. ​does not supply enough information to make it useful
  b. ​reveals the phenotype of the organism
  c. reveals the effects of the environment on the genome
  d. ​reveals how many genes are involved in producing the trait
  e. ​cannot exactly define risks

 

ANSWER:   e
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-1 All the King’s Men
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-1-2 – Identify the capabilities and limitations of genetic technology.

 

22. ​Mendel’s pea plants made good experimental subjects because they ____.

  a. ​exhibit continuous variation
  b. ​exhibit a variety of inheritance patterns
  c. ​exhibit discontinuous variation and complete dominance
  d. ​are sterile
  e. ​have many complex traits that are easy to research

 

ANSWER:   c
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-2 Polygenic Traits Are Controlled by Two or More Genes
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-2-1 – Differentiate between discontinuous and continuous phenotypic variation and identify the genetic conditions under which each occurs.

 

23. ​Genomic technology allows researchers to use ____ to survey the genome to detect associations between common variations and a specific phenotype.

  a. ​pedigrees
  b. ​continuous traits
  c. ​chromosome number
  d. ​nucleotide variations
  e. ​RNA

 

ANSWER:   d
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-8 Genetics of Height: A Closer Look
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-8-1 – Explain how single nucleotide polymorphisms (SNPs) and haplotypes are used to reveal genetic contributions to complex traits such as height.

 

24. ​Spina bifida is one of the most common and most complex birth defects involving the ____ system.

  a. ​nervous
  b. ​circulatory
  c. ​respiratory
  d. ​digestive
  e. ​endocrine

 

ANSWER:   a
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-4 – List the characteristics of spina bifida and examine the genetic and environmental factors that contribute to the variable phenotypes of this disorder.

 

25. ​The ____ model of genetic analysis of complex traits assumes that each gene involved has an equal effect on the phenotype.

  a. ​cumulative
  b. ​additive
  c. ​epigenetic
  d. ​polygenic
  e. ​phenotypic

 

ANSWER:   b
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-4 The Additive Model for Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-4-1 – Distinguish among complex traits, polygenic traits, and multifactorial traits, and describe factors that complicate their analysis.

 

26. ​In obesity studies in mice, the binding of leptin activates the leptin receptor and initiates changes in ____ in the hypothalamus.

  a. ​nucleotide sequences
  b. ​cell membranes
  c. ​mitochondria
  d. ​fat storage
  e. ​gene expression

 

ANSWER:   e
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-4 – Describe how geneticists are using twin studies, animal models, and human genome scanning techniques to study the complex trait of obesity.

 

27. ​Single nucleotide polymorphisms (SNPs) are organized into blocks called ____ and are inherited together.

  a. ​haplotypes
  b. ​chromosome assemblies
  c. ​DNA assemblies
  d. ​multifactorial genes
  e. ​threshold groups

 

ANSWER:   a
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-8 Genetics of Height: A Closer Look
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-8-1 – Explain how single nucleotide polymorphisms (SNPs) and haplotypes are used to reveal genetic contributions to complex traits such as height.

 

28. ​Darker skin color is correlated with ____.

  a. ​the northern hemisphere
  b. ​inland regions
  c. ​coastal regions
  d. ​longitude
  e. ​the intensity of UV radiation

 

ANSWER:   e
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-1 – Demonstrate the relationships of melanin and global latitude distributions to human skin color.

 

29. ​If two genes control a trait and each has a dominant and a recessive allele, there are ____ phenotypic classes in the F2 generation.

  a. ​three
  b. ​five
  c. ​nine
  d. ​sixteen
  e. ​thirty-two

 

ANSWER:   b
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-3 Complex Traits and Variation in Phenotype
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-3-3 – Explain how the number of genes controlling a trait affects the number of phenotypic classes for that trait.

 

30. ​The concept of ____ explains why children of parents who are at the extreme ends of a normal (bell-curve) distribution for a phenotype are usually closer to the population average for the phenotype.

  a. ​correlation coefficient
  b. ​regression to the mean
  c. ​multifactorial differences
  d. ​concordance
  e. ​epigenetics

 

ANSWER:   b
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-4 The Additive Model for Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-4-2 – Describe the concept of regression to the mean and apply it to phenotypic implications in a polygenic system.

 

Completion

 

31. ​An expanded definition of intelligence that goes beyond IQ is called ____________________ and includes verbal and spatial abilities, memory, speed of perception, and reasoning.

ANSWER:   general cognitive ability​
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-3 – Examine how theories about human intelligence have changed from the late eighteenth to the early twenty-first century.

 

32. ​The hormone leptin is produced by ____________________ cells.

ANSWER:   ​fat
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-4 – Describe how geneticists are using twin studies, animal models, and human genome scanning techniques to study the complex trait of obesity.

 

33. ​The correlation coefficient for unrelated people is ____________________.

ANSWER:   0

zero​

DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-6 Heritability Measures the Genetic Contribution to Phenotypic Variation
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-6-1 – Define genetic and environmental variance, and explain how heritability, as measured by the correlation coefficient, is used to quantify the contribution of each to phenotypic variations of complex traits.

 

34. ​Dizygotic twins are no more or less genetically similar than are other pairs of ____________________.

ANSWER:   siblings​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-2 – Illustrate the biology of monozygotic and dizygotic twins, and list the assumptions scientists make when conducting research on twins.

 

35. ​____________________ traits are controlled by two or more genes and significant environmental interactions

ANSWER:   Multifactorial​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-2 Polygenic Traits Are Controlled by Two or More Genes
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-2-2 – Distinguish among complex traits, polygenic traits, and multifactorial traits, and describe factors that complicate their analysis.

 

36. ​Using today’s genetic technology, it is possible to select ____________________ for specific traits.

ANSWER:   embryos​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-1 All the King’s Men
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-1-2 – Identify the capabilities and limitations of genetic technology.

 

37. ​Complex traits are usually quantified by ____________________ rather than by ____________________.

ANSWER:   measurement; counting​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-3 Complex Traits and Variation in Phenotype
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-3-1 – List the distinguishing characteristics of complex traits.

 

38. ​The effect of each dominant allele of a complex trait is ____________________ and _______________.

ANSWER:   ​small; additive
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-4 The Additive Model for Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-4-1 – Distinguish among complex traits, polygenic traits, and multifactorial traits, and describe factors that complicate their analysis.

 

39. ​Along with a significant genetic component, ____________________ plays a significant role in the development of spina bifida.

ANSWER:   nutrition
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-4 – List the characteristics of spina bifida and examine the genetic and environmental factors that contribute to the variable phenotypes of this disorder.

 

40. ​Mutations of some genes for human height result in ____________________.

ANSWER:   skeletal​ defects
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-8 Genetics of Height: A Closer Look
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-8-1 – Explain how single nucleotide polymorphisms (SNPs) and haplotypes are used to reveal genetic contributions to complex traits such as height.

 

41. ​IQ is calculated by dividing the individual’s ____________________ age by his or her ____________________ age and multiplying the quotient by 100.

ANSWER:   mental; chronological​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-3 – Examine how theories about human intelligence have changed from the late eighteenth to the early twenty-first century.

 

42. ​For a complex trait that is observed less frequently in a given sex in a given family, the recurrence risk for this trait is ____________________ for future children of that sex.

ANSWER:   lower​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-3 – Explain how the threshold model and recurrence risk are used to predict phenotypic distributions of complex traits.

 

43. ​In twin studies, geneticists look for situations in which genetic and environmental influences are clearly ____________________.

ANSWER:   separated

separate​

DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-1 – Explain how twin and adoption studies are used to measure environmental and genetic contributions to phenotypic variations of complex traits.

 

44. ​Skin color in humans is a(n) ____________________ trait.

ANSWER:   multifactorial

complex

polygenic

complex multifactorial​

DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-3 Complex Traits and Variation in Phenotype
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-3-2 – Identify several polygenic and multifactorial complex traits in humans.

 

45. ​If only one twin has a trait, the twins are ____________________ for that trait.

ANSWER:   discordant​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-3 – Apply the concept of concordance to the study of heritability of complex traits.

 

46. ​Scientists are researching how much influence ____________________ has on the differences in IQ among population groups often classified as different races.

ANSWER:   inheritance

genetics

environment

the environment​

DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-4 – Debate the controversial issues surrounding IQ and race.

 

47. ​The genotype is fixed at the moment of ____________________ and, barring mutation, is unchanging.

ANSWER:   fertilization​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-1 – Apply basic genetic concepts to the interaction between multiple genes and environmental factors in multifactorial traits.

 

48. ​Animal models such as the ____________________ and ____________________ are being studied to identify single genes that control aspects of learning, memory, and spatial perception.

ANSWER:   fruit fly; mouse
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-5 – Explain why heritability and environmental factors cannot be accurately quantified in the study of human intelligence.

 

49. ​One of the important assumptions made during the study of heritability in twins is that monozygotic twins share all their ____________________ and their ____________________.

ANSWER:   genes; environment​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-2 – Illustrate the biology of monozygotic and dizygotic twins, and list the assumptions scientists make when conducting research on twins.

 

50. ​In humans, variations in skin color are due to differences in the amount, type, and distribution of the pigment ____________________.

ANSWER:   ​melanin
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-1 – Demonstrate the relationships of melanin and global latitude distributions to human skin color.

 

Essay

 

51. ​Define and give examples of discontinuous and continuous phenotypic variation and explain how understanding of these two concepts resulted in important advances in human genetics.

ANSWER:   When a single gene pair controls a trait, such as the tall and short phenotypes in Mendel’s pea plants, the resulting phenotypes will be either tall or short. These two phenotypes are examples of discontinuous phenotypic variation. In contrast, when several gene pairs and environmental interactions control a trait, such as the many phenotypes for human height, the resulting phenotypes will fall into a series of overlapping phenotypic classes. This pattern of phenotypes is an example of continuous phenotypic variation. Understanding the genetics underlying discontinuous and continuous traits was an important advance in human genetics and led to the realization that some traits are controlled by single genes (monogenic traits) identified by classic Mendelian patterns of inheritance, while others are complex traits controlled by multiple factors.​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-2 Polygenic Traits Are Controlled by Two or More Genes
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-2-1 – Differentiate between discontinuous and continuous phenotypic variation and identify the genetic conditions under which each occurs.

 

52. ​Illustrate how the five basic human eye colors can be explained by a model using two genes (A and B), each of which has two alleles (A and a, B and b).

ANSWER:   ​In this model, human eye color is determined by different combinations of alleles of two genes interacting to synthesize and deposit melanin in the iris. If two genes control a trait and each has a dominant and a recessive allele, there are five phenotypic classes in the F2, each of which is controlled by four, three, two, one, or zero dominant alleles. The F2 ratio of 1 : 4 : 6 : 4 : 1 results from the genotypic combinations that produce each phenotype. At one extreme is the homozygous dominant (AABB) genotype with four dominant alleles; at the other extreme is the homozygous recessive (aabb) genotype with no dominant alleles. The largest phenotypic class (6/16) has six genotypic combinations. Combinations of alleles result in small differences in eye color.
DIFFICULTY:   Bloom’s: Analyze
REFERENCES:   5-3 Complex Traits and Variation in Phenotype
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-3-3 – Explain how the number of genes controlling a trait affects the number of phenotypic classes for that trait.

 

53. ​Discuss Sir Francis Galton’s contribution to genetics and identify the important concept that is linked to his observations.

ANSWER:   Sir Francis Galton, a cousin of Charles Darwin, studied the inheritance of many traits in humans. He noticed that children of tall parents were often shorter than their parents and that children of short parents were often taller than their parents. He noted that children of very tall or very short parents are usually closer to the average height of the population rather than the average height of their parents. This important concept is called regression to the mean.​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-4 The Additive Model for Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-4-2 – Describe the concept of regression to the mean and apply it to phenotypic implications in a polygenic system.

 

54. ​Summarize the results of performing genome-wide searches for genes that control obesity.

ANSWER:   The results of several of these genome scans indicate that important genes for obesity are located on nine different chromosomes. One of the early successes in this search was the identification of an allele of the FTO gene as one strongly associated with BMI. Current research efforts are directed at the mechanisms by which these genes confer risk for obesity. Further work may identify additional genes involved in obesity and provide a foundation for studying how these genes interact with environmental factors to cause obesity.​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-7 Twin Studies and Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-7-4 – Describe how geneticists are using twin studies, animal models, and human genome scanning techniques to study the complex trait of obesity.

 

55. ​Describe the breeding program initiated by King Frederick William of Prussia in the early 1700s to supply tall soldiers to the Potsdam Grenadier Guard. Was it successful? Why or why not?

ANSWER:   Frederick William was obsessed with having giants in his Potsdam Grenadier Guards, so he decided to breed giants to serve in his unit. He ordered that every tall man in the kingdom marry a tall, robust woman, expecting that the offspring would all be tall and that some would be giants. Unfortunately, his expectations fell far short of reality. Not only was his program slow (with humans, it takes 18 to 20 years to produce mature adults), but most of the children were actually shorter than their parents. This human breeding experiment ended shortly after the king’s death in 1740.
DIFFICULTY:   Bloom’s: Remember
REFERENCES:   5-1 All the King’s Men
LEARNING OBJECTIVES:   HUHE.CUMM.16. 5-1-2 – Identify the limitations of genetic technology in determining genetic risk for complex traits in human embryos.

 

Figure 5-9

 

56. ​Refer to the figure above to explain the threshold model of complex traits.

ANSWER:   The threshold model explains the discontinuous distribution of some complex traits. In this model, liability for a genetic disorder is distributed among individuals in a normal curve. This liability is caused by a number of genes, each acting additively. Only those individuals who have a genetic liability above a certain threshold are affected if exposed to certain environmental conditions. The severity of the disease usually increases as genetic liability moves away from the mean, and is affected by environmental factors.​
DIFFICULTY:   Bloom’s: Analyze
REFERENCES:   5-5 Multifactorial Traits: Multiple Genes and Environmental Effects
PREFACE NAME:   Figure 5-9
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-5-3 – Explain how the threshold model and recurrence risk are used to predict phenotypic distributions of complex traits.

 

57. ​Summarize and give examples of the relationship between heritability and correlation coefficients and explain how each is calculated.

ANSWER:   Heritability is calculated by using relatives because we know the fraction of genes shared by related individuals. These relationships are expressed as a correlation coefficient or the fraction of genes shared by two relatives. A child receives half of his or her genes from each parent. The half set of genes received by a child from its parent corresponds to a correlation coefficient of 0.5. The genetic relatedness of identical twins is 100%, and the correlation coefficient therefore is 1.0. Unless a mother and a father are related by descent, they should be genetically unrelated, and the correlation coefficient is 0.0. Using the genetic relatedness among population members expressed as a correlation coefficient and using the measured phenotypic variation expressed in quantitative units, a heritability value can be calculated for a specific phenotype in a population. If the heritability value for a trait is 0.72, this means that 72% of the phenotypic variability seen in the population is caused by genetic differences in the population.​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-6 Heritability Measures the Genetic Contribution to Phenotypic Variation
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-6-1 – Define genetic and environmental variance, and explain how heritability, as measured by the correlation coefficient, is used to quantify the contribution of each to phenotypic variations of complex traits.

 

58. ​Describe the relationship between single nucleotide polymorphisms and haplotypes and explain how each is used in genome-wide association studies.

ANSWER:   Genome-wide association studies look for an association between the single nucleotide polymorphism markers and a trait. Haplotypes are combinations of SNPs located so close to each other on a chromosome that they are very often inherited together. In GWAS, researchers scan tens of thousands of genomes to see whether a particular haplotype is found significantly more often in people with a trait than in people without the trait. If so, a gene controlling that trait may be near the chromosome location of these SNPs, and candidate genes near the SNPs can be investigated.​
DIFFICULTY:   Bloom’s: Analyze
REFERENCES:   5-8 Genetics of Height: A Closer Look
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-8-1 – Explain how single nucleotide polymorphisms (SNPs) and haplotypes are used to reveal genetic contributions to complex traits such as height.

 

59. ​Summarize the results of one of the first investigations of the genetics of skin color.

ANSWER:   One of the first investigations of the genetics of skin color, done between 1910 and 1914, studied black–white marriages in Bermuda and in the Caribbean. The results illustrate several properties of traits controlled by more than one gene. The F1 generation had skin colors intermediate to those of their parents. In the F2, a small number of children were as white as one grandparent, a small number were as black as the other grandparent, and most had skin color between those two extremes. Because F2 individuals could be grouped into five phenotypic classes, the investigators hypothesized that two gene pairs control skin color. Each F2 phenotypic class represented a genotype produced by the segregation and assortment of two gene pairs.​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-2 – Explain how the study of black-white marriages in the early 1900s determined that human skin color is a complex trait.

 

60. ​Describe the approach using genomics to identify genes that contribute to the variations in cognitive ability observed in humans.

ANSWER:   This approach uses SNPs and other DNA markers to identify chromosome regions that contain genes related to specific traits. Identifying the number of these regions associated with variation in a specific phenotype is an indirect way of determining whether that phenotype is controlled by many genes, each having a small effect, or by a small number of genes, each with a major effect on the phenotype. One study has provided strong evidence that a large proportion of individual differences in intelligence is due to genetic variation, and that many genes, each with a small additive effect, are involved in these differences.​
DIFFICULTY:   Bloom’s: Understand
REFERENCES:   5-9 Skin Color and IQ Are Complex Traits
LEARNING OBJECTIVES:   HUHE.CUMM.16.5-9-5 – Explain why heritability and environmental factors cannot be accurately quantified in the study of human intelligence.

 

 

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