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					Klug, Concepts of Genetics 8/e
CHAPTER 3 MEDIA REVIEW QUESTIONS

1.   Which of the following factors was not crucial to the success of Gregor
     Mendel's experiments?
     HINT: What methodology is necessary for good experimental biology?
     a. He kept detailed quantitative records.
        Incorrect. This factor was crucial; sometimes subtle differences
        between experimental groups are only revealed through statistical
        analysis. 3.1 Mendel Used a Model Experimental Approach to Study
        Patterns of Inheritance (p. 40)
     b. He chose traits that were not greatly influenced by the environment.
        Incorrect. This factor was crucial; when the environmental
        component of a trait is large, it is hard to know whether genetic or
        environmental causes are responsible for an observed phenotype.
        3.1 Mendel Used a Model Experimental Approach to Study Patterns of
        Inheritance (p. 40)
     c. He always allowed all pea plants to self-fertilize, avoiding
        contamination from other individuals.
        Correct. This was not a factor; Mendel often crossed different
        individuals in his experiments. 3.1 Mendel Used a Model
        Experimental Approach to Study Patterns of Inheritance (p. 40)
     d. He observed only one or two traits in any given experiment.
        Incorrect. This factor was crucial; by keeping his manipulations
        simple, Mendel could interpret his results more easily. 3.1 Mendel
        Used a Model Experimental Approach to Study Patterns of
        Inheritance (p. 40)

2.   True or false? A true-breeding plant is one that is homozygous for the
     trait under study.
     HINT: True-breeding plants always give rise to offspring whose
     phenotypes are just like the parents.
     True. True-breeding plants are homozygous for the trait under study,
     and their offspring always have phenotypes identical to those of the
     parents. 3.1 Mendel Used a Model Experimental Approach to Study
     Patterns of Inheritance (p. 40)

3.   Which two genotypes in an individual would be expressed as the same
     phenotype in a diploid organism?
     HINT: How do genotypes correlate with phenotypes?
     a. Homozygous dominant and homozygous recessive
        Incorrect. The homozygous dominant individual (both alleles
        dominant) would express the dominant phenotype, and the
        homozygous recessive individual (both alleles recessive) would
        express the recessive phenotype. 3.2 The Monohybrid Cross Reveals
        How One Trait Is Transmitted from Generation to Generation (p. 40)
     b. Homozygous dominant and heterozygous
        Correct. Both of these genotypes would express the dominant
        phenotype. The homozygous dominant individual would have both
        copies of the dominant allele, and the heterozygous individual would
        have one copy of the dominant allele and one copy of the recessive
        allele, but only the dominant phenotype would be observed. 3.2 The
        Monohybrid Cross Reveals How One Trait Is Transmitted from
        Generation to Generation (p. 40)
     c. Homozygous recessive and heterozygous
        Incorrect. The homozygous recessive individual (both alleles
        recessive) would express the recessive phenotype, and the
        heterozygous individual would express the dominant phenotype. 3.2
        The Monohybrid Cross Reveals How One Trait Is Transmitted from
        Generation to Generation (p. 40)

4.   True or false? The term phenotype refers to the genetic constitution of
     an individual.
     HINT: The phenotype is the physical result of the genotype’s message.
     False. The term phenotype refers to the appearance of a characteristic
     or trait that results from an individual’s genetic constitution, or
     genotype. 3.2 The Monohybrid Cross Reveals How One Trait Is
     Transmitted from Generation to Generation (p. 40)

5.   A test cross is designed to determine the genotype of a parent with the
     dominant tall phenotype. A test cross produces progeny that are 1⁄2 tall
     and 1⁄2 dwarf. What is the genotype of the parent?
     HINT: A test cross involves a heterozygous or homozygous dominant
     parent and a homozygous recessive parent.
     a. Dd
        Correct. The tall parent must be heterozygous because we know the
        dwarf parent is homozygous recessive, by definition of the test cross,
        and the only way to produce 1/2 recessive offspring is for the tall
        parent to be heterozygous. 3.2 The Monohybrid Cross Reveals How
        One Trait Is Transmitted from Generation to Generation (p. 40)
     b. DD
        Incorrect. The tall parent genotype must be capable of combining
        with the recessive genes of the other parent to produce either Dd or
        dd offspring. 3.2 The Monohybrid Cross Reveals How One Trait Is
        Transmitted from Generation to Generation (p. 40)
     c. dd
        Incorrect. The tall parent genotype must be capable of combining
        with the recessive genes of the other parent to produce either Dd or
        dd offspring. 3.2 The Monohybrid Cross Reveals How One Trait Is
        Transmitted from Generation to Generation (p. 40)
     d. D
        Incorrect. The tall parent genotype must be diploid and capable of
        combining with the recessive genes of the other parent to produce
        either Dd or dd offspring. 3.2 The Monohybrid Cross Reveals How
        One Trait Is Transmitted from Generation to Generation (p. 40)
6.   What ratio of offspring would be expected from a cross of individuals
     who are heterozygous for height and color? (Assume that tall is
     dominant to dwarf and green is dominant to yellow.)
     HINT: Use a Punnett square or the forked-line method to analyze this
     dihybrid cross.
     a. 3 tall green:1 dwarf short
        Incorrect. This ratio would be expected for a monohybrid cross. 3.3
        Mendel's Dihybrid Cross Revealed His Fourth Postulate: Independent
        Assortment (p. 44)
     b. 1 tall green:1 tall yellow:1 dwarf green:1 dwarf yellow
        Incorrect. This would be the result of a test cross with a double
        heterozygote. 3.3 Mendel's Dihybrid Cross Revealed His Fourth
        Postulate: Independent Assortment (p. 44)
     c. All tall green plants
        Incorrect. Some homozygous recessive plants (dwarf yellow) are
        likely to be produced when heterozygotes are crossed. 3.3 Mendel's
        Dihybrid Cross Revealed His Fourth Postulate: Independent
        Assortment (p. 44)
     d. 9 tall green:3 tall yellow:3 dwarf green:1 dwarf yellow
        Correct. The 9:3:3:1 ratio is expected for a dihybrid cross of
        heterozygotes when the traits are independently assorting. 3.3
        Mendel's Dihybrid Cross Revealed His Fourth Postulate: Independent
        Assortment (p. 44)

7.   How many different types of gametes can be formed by individuals with
     genotype AaBbcc?
     HINT: Match each A or a with each B or b and each c in combinations of
     three to get the different types of gametes.
     a. AaBbcc
        Incorrect. cc produces only one kind of gamete c. How many
        gametes can Aa and Bb produce? Combine them using the forked-
        line method. 3.4 The Trihybrid Cross Demonstrates That Mendel's
        Principles Apply to Inheritance of Multiple Traits (p. 47)
     b. ABc, Abc
        Incorrect. cc produces only one kind of gamete c. How many
        gametes can Aa and Bb produce? Combine them using the forked-
        line method. 3.4 The Trihybrid Cross Demonstrates That Mendel's
        Principles Apply to Inheritance of Multiple Traits (p. 47)
     c. ABc, Abc, aBc
        Incorrect. cc produces only one kind of gamete c. How many
        gametes can Aa and Bb produce? Combine them using the forked-
        line method. 3.4 The Trihybrid Cross Demonstrates That Mendel's
        Principles Apply to Inheritance of Multiple Traits (p. 47)
     d. ABc, Abc, aBc, abc
        Correct. These are the four possible gamete combinations. 3.4 The
        Trihybrid Cross Demonstrates That Mendel's Principles Apply to
        Inheritance of Multiple Traits (p. 47)
8.   How did Mendel's work support the chromosomal theory of inheritance?
     HINT: Mendel observed the results of chromosome assortment during
     sexual reproduction.
     a. The behavior of chromosomes during meiosis (as observed under a
        microscope) correlated with Mendel’s principles of inheritance.
        Correct. The observation that chromosomes segregated
        independently and randomly during meiosis fit very nicely with
        Mendel’s postulates. Mendel’s work supported the idea that the
        genetic information was carried on the chromosomes. 3.6 The
        Correlation of Mendel's Postulates with the Behavior of Chromosomes
        Formed the Foundation of Modern Transmission Genetics (p. 49)
     b. Mendel’s work matched with the continuous variation theory.
        Incorrect. Continuous variation proponents believed in a blending of
        parental traits in the offspring, which is in opposition to Mendel’s
        work. 3.6 The Correlation of Mendel's Postulates with the Behavior of
        Chromosomes Formed the Foundation of Modern Transmission
        Genetics (p. 49)
     c. Mendel’s statistical evidence of gene segregation indicated the
        involvement of chromosomes.
        Incorrect. Mendel’s statistical evidence of gene segregation, together
        with observation of the movement of chromosomes during meiosis,
        led to the chromosomal theory of inheritance. However, the
        statistical evidence alone did not. 3.6 The Correlation of Mendel's
        Postulates with the Behavior of Chromosomes Formed the
        Foundation of Modern Transmission Genetics (p. 49)
     d. The traits that Mendel studied were known to lie on chromosomes.
        Incorrect. During Mendel’s time, chromosomes had not yet been
        observed. 3.6 The Correlation of Mendel's Postulates with the
        Behavior of Chromosomes Formed the Foundation of Modern
        Transmission Genetics (p. 49)

9.   On the basis of segregation and independent assortment, how many
     different types of gametes can be formed from an organism that has a
     diploid number of 12?
     HINT: The number of different types of gametes formed is based on the
     number of complementary chromosomes found in the genome.
     a. 1
         Incorrect. For a diploid organism with twelve chromosomes, there is
         the possibility of forming at least 24 different gametes. 3.7
         Independent Assortment Leads to Extensive Genetic Variation (p. 51)
     b. 2
         Incorrect. To determine the number of different types of gametes
         possible, the number of copies of each chromosome (e.g., two copies
         of each in a diploid organism) should be raised to the nth power,
         where n equals the haploid number of chromosomes. Two is not the
         correct answer using this method. 3.7 Independent Assortment
         Leads to Extensive Genetic Variation (p. 51)
    c. 12
       Incorrect. To determine the number of different types of gametes
       possible, the number of copies of each chromosome (e.g., two copies
       of each in a diploid organism) should be raised to the nth power,
       where n equals the haploid number of chromosomes. Twelve is not
       the correct answer using this method. 3.7 Independent Assortment
       Leads to Extensive Genetic Variation (p. 51)
    d. 64
       Correct. If the number of complementary chromosomes in the
       genome (two because it is a diploid) is raised to the nth power
       (where n = haploid number = 1/2 of the diploid number 12, or 6),
       the answer is 64. 3.7 Independent Assortment Leads to Extensive
       Genetic Variation (p. 51)

10. A conditional probability is one for which
    HINT: Conditional probabilities are useful to genetic counselors
    a. Two independent events must occur
       Incorrect. In conditional probability, the second event is dependent
       upon the first occurring. 3.8 Laws of Probability Help to Explain
       Genetic Events (p. 51)
    b. The binomial theorem must be applied to determine an event's
       likelihood of occurrence
       Incorrect. The probability of two events occurring must simply be
       multiplied. 3.8 Laws of Probability Help to Explain Genetic Events (p.
       51)
    c. A specific condition must occur before the event of interest in can
       occur
       Correct. If the initial condition does not occur, the event of interest
       cannot occur. 3.8 Laws of Probability Help to Explain Genetic Events
       (p. 51)
    d. The probability of an event occurring can never be determined
       Incorrect. Conditional probability is the probability of an event
       occurring, given that another event has occurred. 3.8 Laws of
       Probability Help to Explain Genetic Events (p. 51)

11. The chi-square analysis can help us to decide whether
    HINT: Statistical analysis gives us a mathematical tool for evaluating
    data.
    a. Our expectations for an experiment are correct
       Incorrect. Statistics can't tell us whether something is right or wrong.
       3.9 Chi-Square Analysis Evaluates the Influence of Chance on
       Genetic Data (p. 54)
    b. Our observations of an event differ from our expectations
       Correct. This is exactly the purpose of statistical tests. 3.9 Chi-
       Square Analysis Evaluates the Influence of Chance on Genetic Data
       (p. 54)
    c. A hypothesis is correct
       Incorrect. It just helps us decide whether to reject a hypothesis. 3.9
       Chi-Square Analysis Evaluates the Influence of Chance on Genetic
       Data (p. 54)
    d. Our experiment was conducted properly
       Incorrect. Our observations may differ from our expectations for
       many different reasons. 3.9 Chi-Square Analysis Evaluates the
       Influence of Chance on Genetic Data (p. 54)

12. What information can be obtained from a human pedigree?
    HINT: Human pedigrees show the transmission of genetic traits through
    several generations in a family.
    a. How a gene is inherited
       Correct. Human pedigrees are useful for determining the mode of
       inheritance of a gene; for example, whether it is passed as a
       dominant, recessive, or sex-linked trait. 3.10 Pedigrees Reveal
       Patterns of Inheritance in Humans (p. 56)
    b. The type of mutation that caused a specific genetic trait
       Incorrect. Human pedigrees do not show the mutations that occurred
       on the DNA level to confer the expressed trait. 3.10 Pedigrees Reveal
       Patterns of Inheritance in Humans (p. 56)
    c. How the mutation occurred
       Incorrect. Human pedigrees do not give information about how a
       mutation occurred. The mechanism by which a mutation occurred
       might be determined by analyzing the gene at the DNA level. 3.10
       Pedigrees Reveal Patterns of Inheritance in Humans (p. 56)
    d. Where the gene is located on a chromosome
       Incorrect. If known DNA markers segregated with a specific
       phenotype, a pedigree could help determine where the gene is
       located on a chromosome. However, the pedigree by itself could not
       give this information. 3.10 Pedigrees Reveal Patterns of Inheritance
       in Humans (p. 56)

13. Mendel's cross of the true-breeding round and wrinkled parents
    produced all round progeny peas in the F1 generation. Assume that
    round shape is dominant to wrinkled. What kind of cross was made in
    the P1 generation?
    HINT: Consider the genotypes of the P1 generation.
    a. Self-cross
       Incorrect. The two parents have different genotypes.
    b. Genetic cross
       Incorrect. While the cross is a genetic cross, there is a better answer.
    c. Test cross
       Incorrect. A test cross uses a homozygous recessive individual to test
       the genotype of one of the parents.
    d. Monohybrid cross
       Correct. The P1 cross is a monohybrid cross between a homozygous
       dominant and a homozygous recessive individual.
14. Mendel's unit factors in pairs are most accurately known to be
    HINT: Review Mendel's work and his observations on the segregation of
    traits in pea plants.
    a. Two maternal chromatids
        Incorrect. Chromatids consist of two daughter strands of a duplicated
        chromosome joined together by a centromere. The maternal
        chromatid carries one copy of a unit factor, but its pair would come
        from the paternal chromatid.
    b. Two alleles on nonhomologous chromosomes
        Incorrect. Two alleles on nonhomologous chromosomes would be
        representatives of two different genes. Mendel's unit factors in pairs
        refers to alleles on homologous chromosomes.
    c. Two alleles on paternal and maternal homologs
        Correct. Mendel observed patterns of inheritance in offspring that
        stemmed from traits found in the parents. Mendel explained this
        phenomenon as the transmission of "unit factors" from the parents to
        the offspring.
    d. Identical alleles on homologous chromosomes
        Incorrect. Unit factors can be, but are not necessarily, identical
        alleles on homologous chromosomes.

15. Normal parents have a child with Tay-Sachs disease, a recessive
    condition. What is the probability that their next child will be normal?
    HINT: A recessive disorder requires an individual to have two copies of
    the mutated gene to be observed in the phenotype.
    a. 0.00 (0%)
       Incorrect. If two normal individuals have one child with Tay-Sachs
       disease, they are both heterozygous carriers for the recessive gene.
       Two heterozygous carriers will not produce recessive offspring 100%
       of the time.
    b. 0.25 (25%)
       Incorrect. If two normal individuals have one child with Tay-Sachs
       disease, they are both heterozygous carriers for the recessive gene.
       The recessive disorder will be seen approximately 25% of the time. A
       normal child with either a homozygous dominant or heterozygous
       genotype would occur more than 25% of the time.
    c. 0.75 (75%)
       Correct. If two normal individuals have one child with Tay-Sachs
       disease, they are both heterozygous carriers for the recessive gene.
       The probability of producing a child that is either homozygous
       dominant or heterozygous for the Tay-Sachs gene is 3:1 for every
       meiotic event. Thus, the chances for the next child to be normal are
       75%.
    d. 1.0 (100%)
       Incorrect. If two normal individuals have one child with Tay-Sachs
       disease, they are both heterozygous carriers for the recessive gene.
       The next child will have the same chance of getting both copies of
        the recessive gene as the first child. Thus, it is impossible that the
        next child has a 100% chance of being normal.

16. Sickle cell anemia is an autosomal recessive disease. A man whose
    father had sickle cell anemia, but does not himself have the disease,
    marries a woman whose mother had sickle cell anemia, but does not
    herself have the disease. Which of the following statements is false?
    HINT: Construct a Punnett square to determine the genotype of each
    parent and the possible genotypes of their children.
    a. They can produce offspring that are neither carriers of the trait nor
        affected with sickle cell anemia.
        Incorrect. This statement is true because both parents must be
        heterozygous.
    b. All of their offspring must be carriers of the sickle cell allele.
        Correct. This statement is false. On average, one-quarter of their
        children will not carry the sickle cell allele.
    c. If their first two children do not have sickle cell anemia, the chances
        of the third having the disease is one in four.
        Incorrect. This statement is true. Because the genotypes of the
        parents are known, the odds of having a child with the disease do
        not change no matter how many children they have.
    d. About three-fourths of their offspring, on average, can be expected
        to have at least one sickle cell allele.
        Incorrect. This statement is true when heterozygous individuals are
        crossed.

17. If a home garden were planted with all hybrid round peas, what
    phenotypic proportions would be observed in the progeny? (The wrinkled
    trait is recessive.)
    HINT: Consider the genotype of the parental plants.
    a. 4/4 round
        Incorrect. The hybrid round peas have a heterozygous genotype.
    b. 1/4 round and 3/4 wrinkled
        Incorrect. The hybrid round peas have a heterozygous genotype.
    c. 2/4 round and 2/4 wrinkled
        Incorrect. The hybrid round peas have a heterozygous genotype.
    d. 3/4 round and 1/4 wrinkled
        Correct. The hybrid round peas are heterozygous, and therefore the
        expected ratio of round to wrinkled peas (if the round trait is
        dominant) will be 3:1.

18. Which of the following statements is an example of independent
    assortment?
    HINT: One of Mendel's two most important discoveries was that traits
    assort independently of one another.
    a. An individual with red hair is no more or less likely to be tall than
       anyone else.
        Correct. Traits that are not on the same chromosome are inherited
        independently of one another.
     b. More men than women are color-blind.
        Incorrect. This is an example of a sex-linked trait.
     c. Some traits are more likely to be inherited than others.
        Incorrect. All single-gene traits are inherited in the same way.
     d. A diploid individual passes on only one copy of a gene to her
        offspring.
        Incorrect. This is an example of segregation.

19. If a family has five children, what is the probability that four of them are
    girls?
    HINT: This question is asking what the probability is of having one boy
    out of five children.
    a. 5 (1/2)4 (1/2)1
        Correct. Check the use of the binomial expansion or Pascal's triangle.
    b. (0.5  0.5  0.5  0.5  0.5)
        Incorrect. Consider the probability of having just one boy, born first.
        Then consider other possible options.
    c. 1/5  1/5  1/5  1/5  1/5
        Incorrect. The probability that any given child is a boy is 0.5.
    d. 5 [(0.5 + 0.5 + 0.5 + 0.5 + 0.5)/5]
        Incorrect. Consider the probability of having just one boy, born first.
        Then consider other possible options.

20. Round (R) seed shape is dominant to wrinkled (r) seed shape in pea
    plants. If an RR plant is crossed with an rr plant, what is the frequency
    of phenotypes in the F2 generation?
    HINT: Use a Punnett square to determine the phenotypes.
    a. 1/4 RR, 1/2 Rr, 1/4 rr
        Incorrect. This is the frequency of the genotypes in the F2
        generation.
    b. 3 round seeds, 1 wrinkled seed
        Correct. The F1 generation would have the genotype Rr, so crossing
        two heterozygotes would result in 3 plants with round seeds and 1
        plant with wrinkled seeds.
    c. All round seeds
        Incorrect. The F1 generation would have all round seeds.
    d. All wrinkled seeds
        Incorrect. The wrinkled allele is recessive to the round allele.

21. If the first three F2 offspring grown from the cross described above are
    round, what is the probability that the next F2 offspring will be wrinkled?
    HINT: Think about Mendel’s postulates of inheritance.
    a. 0%
        Incorrect. The proportion of rr is still 1/4, no matter how many round
        offspring have been observed.
    b. 100%
        Incorrect. The proportion of rr is still 1/4, no matter how many round
        offspring have been observed.
     c. 25%
        Correct. The proportion of rr is 1/4, so the next offspring has a 25%
        chance of being wrinkled.
     d. 75%
        Incorrect. The proportion of rr is still 1/4, no matter how many round
        offspring have been observed.

22. True or false? The law of independent assortment states that one gene
    in a pair is always dominant to the other.
    HINT: What is the law of independent assortment?
    False. The law of independent assortment states that during gamete
    formation, segregating pairs of unit factors assort independently of each
    other; the law says nothing about dominance.

23. If a yellow pea plant with round seeds that has the genotype GgWw is
    crossed to itself, what proportion of the offspring will be green with
    round seeds?
    HINT: Predict all possible gamete combinations and then use the forked-
    line method to predict the probability of all possible phenotypes.
    a. 3/16
        Correct. This is the probability of offspring that are either green with
        round seeds or yellow with wrinkled seeds.
    b. 9/16
        Incorrect. This is the probability of offspring that are yellow with
        round seeds.
    c. 1/16
        Incorrect. This is the probability of offspring that are green with
        wrinkled seeds.
    d. 0
        Incorrect. It is possible to obtain offspring that are green with round
        seeds from this cross.

24. What is the probability of a family with six children having three boys
    and three girls?
    HINT: Use the binomial theorem and Pascal’s triangle.
    a. 1/64
       Incorrect. This would be the coefficient of the first (a6) and last (b6)
       terms in the expansion (a + b)6.
    b. 6/64
       Incorrect. This would be the coefficient of the second (a5)(b) and
       sixth (a)(b5) terms in the expansion (a + b)6.
    c. 15/64
       Incorrect. This would be the coefficient of the third (a4)(b2) and fifth
       (a2)(b4) terms in the expansion (a + b)6.
    d. 20/64
        Correct. The term of interest in the expansion (a + b)6 is the middle
        term: (a3)(b3). Using Pascal’s triangle, the coefficient of this term is
        20, so the probability of three boys and three girls is 20/64.

25. Which term describes the individual in a pedigree whose phenotype was
    first brought to the attention of a medical researcher?
    HINT: Review the terminology used in a pedigree.
    a. Progeny
        Incorrect. Progeny are offspring.
    b. Sibship
        Incorrect. A sibship line is used to denote siblings in a pedigree.
    c. Proband
        Correct. The proband is the affected individual who is first brought to
        the attention of a medical researcher; usually the pedigree is
        constructed around this individual.
    d. Allele
        Incorrect. Alleles are alternative forms of a single gene.

				
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