What Are The Genotype And Phenotype? Quiz

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Botany Quizzes & Trivia

Questions and Answers
  • 1. 

    Pea plants were particularly well suited for use in Mendel's breeding experiments for all of the following reasons except that

    • A.

      Peas show easily observed variations in a number of characters, such as pea shape and flower color.

    • B.

      Many of the observable characters that vary in pea plants are controlled by single genes.

    • C.

      Peas have an unusually long generation time.

    • D.

      It is possible to control matings between different pea plants.

    • E.

      It is possible to obtain large numbers of progeny from any given cross.

    Correct Answer
    C. Peas have an unusually long generation time.
    Explanation
    Peas have an unusually long generation time.

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  • 2. 

    What is the difference between a monohybrid cross and a dihybrid cross?

    • A.

      A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations

    • B.

      A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents.

    • C.

      A monohybrid cross results in a 9:3:3:1 ratio whereas a dihybrid cross gives a 3:1 ratio.

    • D.

      A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid only for one.

    Correct Answer
    D. A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid only for one.
    Explanation
    The difference between a monohybrid cross and a dihybrid cross is that a dihybrid cross involves organisms that are heterozygous for two characters, while a monohybrid cross only involves organisms that are heterozygous for one character. This means that in a dihybrid cross, the offspring will inherit two different traits from each parent, while in a monohybrid cross, the offspring will only inherit one trait from each parent.

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  • 3. 

     A cross between homozygous purple-flowered and homozygous white-flowered pea plants results in offspring with purple flowers. This demonstrates:

    • A.

      Dominance

    • B.

      The blending model of genetics

    • C.

      The mistakes made by Mendel

    • D.

      True-breeding

    • E.

      A dihybrid cross

    Correct Answer
    A. Dominance
    Explanation
    The fact that the offspring of the cross between homozygous purple-flowered and homozygous white-flowered pea plants have purple flowers indicates dominance. This means that the purple flower trait is dominant over the white flower trait, resulting in the expression of the dominant trait in the offspring. This supports the principle of dominance in genetics, where one allele masks the expression of another allele in a heterozygous individual.

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  • 4. 

    The F1 offspring of Mendel;s classic pea cross alwaus looked like one of the two parental varieties because:

    • A.

      No genes interacted to produce the parental phenotype

    • B.

      One phenotype was completely dominant over another

    • C.

      Different genes interacted to produce the parental phenotype

    • D.

      Each allele affected phenotypic expression

    • E.

      The traits blended together during fertilisation

    Correct Answer
    B. One phenotype was completely dominant over another
    Explanation
    The F1 offspring of Mendel's classic pea cross always looked like one of the two parental varieties because one phenotype was completely dominant over another. This means that one of the alleles for a particular trait completely masks the expression of the other allele. As a result, only the dominant phenotype is observed in the offspring, while the recessive phenotype remains hidden. This is the principle of dominance in Mendelian genetics, where the dominant allele determines the physical appearance of the organism.

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  • 5. 

    What was the most significant conclusion that Gregory Mendel drew from his experiments with pea plants?

    • A.

      Genes are composed of DNA

    • B.

      Traits are inherited in discrete units, and are not the results of blending

    • C.

      An organism that is homozygous for many recessive traitsis at a disadvantage

    • D.

      There is considerable genetic variation in garen peas

    • E.

      Recessive genes occur more frequently in the F1 than do dominant ones.

    Correct Answer
    B. Traits are inherited in discrete units, and are not the results of blending
    Explanation
    Gregory Mendel drew the most significant conclusion from his experiments with pea plants that traits are inherited in discrete units, and are not the result of blending. Mendel's experiments showed that traits are passed down from parents to offspring in a predictable and independent manner, rather than being a mixture or blend of parental traits. This concept of discrete inheritance, now known as Mendelian inheritance, laid the foundation for the field of genetics.

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  • 6. 

    How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?

    • A.

      16

    • B.

      64

    • C.

      8

    • D.

      4

    • E.

      32

    Correct Answer
    C. 8
    Explanation
    The genotype AaBbCCDdEE indicates that the individual has 2 alleles for each of the 5 different genes (A, B, C, D, E). Through independent assortment, these alleles can segregate independently into different gametes. Since there are 5 different genes, each with 2 alleles, the total number of possible combinations is 2^5, which equals 32. However, since each gamete can only have one allele per gene, we need to divide this number by 2 for each gene, resulting in 32/2^5 = 8 unique gametes that could be produced.

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  • 7. 

    Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. This suggests

    • A.

      Incomplete dominance.

    • B.

      That the parents were both heterozygous.

    • C.

      That each offspring has the same alleles.

    • D.

      That the parents were true-breeding for contrasting traits.

    • E.

      That a blending of traits has occurred.

    Correct Answer
    B. That the parents were both heterozygous.
    Explanation
    The 3:1 ratio suggests that the trait is controlled by a single gene with two alleles. If the parents were both heterozygous (having different alleles for the trait), they would each contribute one of their alleles to the offspring, resulting in a 3:1 ratio. If the parents were true-breeding for contrasting traits, the ratio would be different. Incomplete dominance and blending of traits would result in different ratios as well. Therefore, the most likely explanation is that the parents were both heterozygous.

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  • 8. 

    Two characters that appear in a 9:3:3:1 ratio in the F2 generation should have which of the following properties?

    • A.

      Each of the traits is controlled by single genes.

    • B.

      The genes controlling the characters obey the law of independent assortment.

    • C.

      Four genes are involved.

    • D.

      Sixteen different phenotypes are possible.

    • E.

      Each of the genes controlling the characters has two alleles.

    Correct Answer
    B. The genes controlling the characters obey the law of independent assortment.
    Explanation
    The presence of a 9:3:3:1 ratio in the F2 generation suggests that the genes controlling the characters obey the law of independent assortment. This means that the genes for the two characters are located on different chromosomes or are far apart on the same chromosome, allowing them to assort independently during gamete formation. If the genes were linked or close together on the same chromosome, they would not segregate independently and the ratio would be different. Therefore, the correct answer is that the genes controlling the characters obey the law of independent assortment.

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  • 9. 

    A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

    • A.

      HhTt

    • B.

      Tt

    • C.

      Hh

    • D.

      T

    • E.

      HT

    Correct Answer
    E. HT
    Explanation
    In this question, the organism's genotype is HhTt. This means that it has one dominant allele for head shape (H) and one recessive allele for head shape (h), as well as one dominant allele for tail length (T) and one recessive allele for tail length (t). During gamete formation, each parent contributes one allele for each gene to the offspring. Since the genes for head shape and tail length are unlinked, they can segregate independently. Therefore, it is possible for a gamete from this organism to contain the alleles HT, which represents a combination of the dominant alleles for head shape and tail length.

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  • 10. 

    It was important that Mendel examined not just the F1 generation in his breeding experiments, but the F2 generation as well, because

    • A.

      Parental traits that were not observed in the F1 reappeared in the F2.

    • B.

      He obtained very few F1 progeny, making statistical analysis difficult.

    • C.

      Analysis of the F1 progeny would have allowed him to discover the law of segregation, but in the law of independent assortment.

    • D.

      The dominant phenotypes were visible in the F2 generation, but not in the F1.

    • E.

      Many of the F1 progeny died.

    Correct Answer
    A. Parental traits that were not observed in the F1 reappeared in the F2.
    Explanation
    Mendel examined the F2 generation in his breeding experiments because parental traits that were not observed in the F1 generation reappeared in the F2. This observation was crucial for Mendel to understand the principles of inheritance and develop his laws of genetics. By studying the F2 generation, Mendel was able to determine that traits can be masked in one generation and reappear in the next, leading to the discovery of dominant and recessive traits. This allowed him to establish the fundamental principles of inheritance and lay the foundation for modern genetics.

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  • 11. 

    When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?

    • A.

      0%

    • B.

      25%

    • C.

      50%

    • D.

      75%

    • E.

      100%

    Correct Answer
    C. 50%
    Explanation
    When crossing an organism that is homozygous recessive for a single trait with a heterozygote, the chance of producing an offspring with the homozygous recessive phenotype is 50%. This is because when crossing a homozygous recessive (rr) with a heterozygote (Rr), there is a 50% chance of the offspring inheriting the recessive allele from the homozygous recessive parent.

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  • 12. 

    Mendel accounted for the observation that traits which had disappeared in the F1 generation reappeared in the F2 generation by proposing that

    • A.

      Traits can be dominant or recessive, and the recessive traits were obscured by the dominant ones in the F1.

    • B.

      The traits were lost in the F1 due to blending of the parental traits.

    • C.

      Members of the F1 generation had only one allele for each character, but members of the F2 had two alleles for each character.

    • D.

      New mutations were frequently generated in the F2 progeny, "reinventing" traits that had been lost in the F1.

    • E.

      The mechanism controlling the appearance of traits was different between the F1 and the F2 plants.

    Correct Answer
    A. Traits can be dominant or recessive, and the recessive traits were obscured by the dominant ones in the F1.
    Explanation
    Mendel proposed that traits can be dominant or recessive, and the recessive traits were obscured by the dominant ones in the F1 generation. This means that in the first generation, only the dominant traits were visible while the recessive traits were not expressed. However, in the F2 generation, when the F1 plants were crossed, the recessive traits reappeared because they were present in the genetic makeup of the F1 plants, even though they were not visible in the previous generation.

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  • 13. 

    Which of the following about the law of segregation is false?

    • A.

      It is a method that can be used to determine the number of chromosomes in a plant.

    • B.

      It states that each of two alleles for a given trait segregate into different gametes.

    • C.

      It can account for the 3:1 ratio seen in the F2 generation of Mendel's crosses.

    • D.

      It can be used to predict the likelihood of transmission of certain genetic diseases within families.

    • E.

      It can be explained by the segregation of homologous chromosomes during meiosis.

    Correct Answer
    A. It is a method that can be used to determine the number of chromosomes in a plant.
    Explanation
    The law of segregation is not a method to determine the number of chromosomes in a plant, but rather a principle that states that each of two alleles for a given trait segregate into different gametes. This principle helps to explain the 3:1 ratio seen in the F2 generation of Mendel's crosses and can be used to predict the likelihood of transmitting certain genetic diseases within families. It is also explained by the segregation of homologous chromosomes during meiosis.

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  • 14. 

    The fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment most probably indicates which of the following? 

    • A.

      The diploid number of chromosomes in the pea plants was 7.

    • B.

      None of the traits obeyed the law of segregation.

    • C.

      All of the genes controlling the traits were located on the same chromosome.

    • D.

      All of the genes controlling the traits behaved as if they were on different chromosomes.

    • E.

      The formation of gametes in plants occurs by mitosis only.

    Correct Answer
    D. All of the genes controlling the traits behaved as if they were on different chromosomes.
    Explanation
    The fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment most probably indicates that all of the genes controlling the traits behaved as if they were on different chromosomes. This means that the genes for these traits were located on different chromosomes and were not linked together. As a result, they were able to independently assort and segregate during the formation of gametes, leading to the observed patterns of inheritance.

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  • 15. 

    Mendel was able to draw his ideas of segregation and independent assortment because of the influence of which of the following? 

    • A.

      His experiments with the breeding of plants such as peas

    • B.

      The understanding of particulate inheritance he learned from renowned scientists of his time

    • C.

      His discussions of heredity with his colleagues at major universities

    • D.

      His reading of the scientific literature current in the field

    • E.

      His reading and discussion of Darwin's Origin of Species

    Correct Answer
    A. His experiments with the breeding of plants such as peas
    Explanation
    Mendel was able to draw his ideas of segregation and independent assortment because of his experiments with the breeding of plants such as peas. Through his experiments, Mendel observed the patterns of inheritance and discovered that traits are passed down in a predictable manner. This led him to develop the principles of segregation and independent assortment, which laid the foundation for modern genetics. Mendel's experiments provided empirical evidence for his theories and allowed him to formulate his groundbreaking laws of inheritance.

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  • 16. 

    Mendel's observation of the segregation of alleles in gamete formation has its basis in which of the following phases of cell division? 

    • A.

      Anaphase of mitosis

    • B.

      Prophase I of meiosis

    • C.

      Anaphase I of meiosis

    • D.

      Metaphase I of meiosis

    • E.

      Prophase II of meiosis

    Correct Answer
    C. Anaphase I of meiosis
    Explanation
    During anaphase I of meiosis, homologous chromosomes separate and move to opposite poles of the cell. This segregation of alleles occurs as the chromosomes separate, ensuring that each gamete receives one allele from each homologous pair. Therefore, Mendel's observation of the segregation of alleles in gamete formation is based on anaphase I of meiosis.

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  • 17. 

    Mendel's second law of independent assortment has its basis in which of the following events of meiosis I?

    • A.

      Alignment of tetrads at the equator

    • B.

      Crossing over

    • C.

      Synapsis of homologous chromosomes

    • D.

      Separation of cells at telophase

    • E.

      separation of homologs at anaphase

    Correct Answer
    A. Alignment of tetrads at the equator
    Explanation
    The alignment of tetrads at the equator is the event in meiosis I that forms the basis of Mendel's second law of independent assortment. This is because during this stage, homologous pairs of chromosomes line up randomly along the equator of the cell, leading to the random distribution of alleles into gametes. This random alignment and segregation of chromosomes during meiosis I is what allows for the independent assortment of different traits and the creation of unique combinations of alleles in offspring.

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  • 18. 

    Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of the cross BbTt × BBtt will have black fur and long tails?  

    • A.

      1/2

    • B.

      1/16

    • C.

      3/16

    • D.

      3/8

    • E.

      9/16

    Correct Answer
    A. 1/2
    Explanation
    When crossing BbTt with BBtt, we can determine the possible genotypes of the offspring. The BbTt parent can produce four different gametes (BT, Bt, bT, bt) while the BBtt parent can only produce one type of gamete (Bt). When these gametes combine, the possible genotypes of the offspring are BTBt, BtBt, bTBt, and btBt. Among these genotypes, only half of them (BTBt and BtBt) have black fur (B) and long tails (T). Therefore, the fraction of the progeny with black fur and long tails is 1/2.

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  • 19. 

    In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short? 

    • A.

      1/6

    • B.

      1/2

    • C.

      1

    • D.

      1/4

    • E.

      0

    Correct Answer
    B. 1/2
    Explanation
    When a heterozygous plant (Tt) is crossed with a homozygous tall plant (TT), the possible genotypes of the offspring are Tt and TT. Since tall (T) is dominant to short (t), both genotypes will result in tall plants. Therefore, there is no possibility of the offspring being short. The probability of the offspring being short is 0, which is not one of the given answer choices.

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  • 20. 

    Two true-breeding stocks of pea plants are crossed. One parent has red, axial flowers and the other has white, terminal flowers; all F1 individuals have red, axial flowers. The genes for flower color and location assort independently. If 1,000 F2 offspring resulted from the cross, approximately how many of them would you expect to have red, terminal flowers?

    • A.

      750

    • B.

      65

    • C.

      565

    • D.

      190

    • E.

      250

    Correct Answer
    D. 190
    Explanation
    In this question, it is stated that the genes for flower color and location assort independently. This means that the inheritance of flower color and location are not linked to each other. Since all F1 individuals have red, axial flowers, we know that they must be heterozygous for flower color (Rr) and homozygous for flower location (aa). When these F1 individuals are crossed, there is a 25% chance of producing offspring with red, terminal flowers (rrAA). Since there are 1,000 F2 offspring, approximately 25% of them would be expected to have red, terminal flowers, which is 190.

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  • 21. 

    In a cross AaBbCc × AaBbCc, what is the probability of producing the genotype AABBCC?

    • A.

      1/64

    • B.

      1/4

    • C.

      1/16

    • D.

      1/8

    • E.

      1/32

    Correct Answer
    A. 1/64
    Explanation
    The probability of producing the genotype AABBCC can be calculated by multiplying the probability of each allele pairing. Since each parent has two copies of each allele, the probability of producing AABBCC is (1/2) * (1/2) * (1/2) * (1/2) * (1/2) * (1/2) = 1/64.

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  • 22. 

    Given the parents AABBCc × AabbCc, assume simple dominance and independent assortment. What proportion of the progeny will be expected to phenotypically resemble the first parent?

    • A.

      3/4

    • B.

      1/4

    • C.

      3/8

    • D.

      1

    • E.

      1/8

    Correct Answer
    A. 3/4
    Explanation
    Assuming simple dominance and independent assortment, the proportion of the progeny that will be expected to phenotypically resemble the first parent is 3/4. This means that out of every 4 progeny, 3 will have phenotypes similar to the first parent.

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  • 23. 

    In snapdragons, heterozygotes for one of the genes have pink flowers, whereas homozygotes have red or white flowers. When plants with red flowers are crossed with plants with white flowers, what proportion of the offspring will have pink flowers?

    • A.

      0%

    • B.

      100%

    • C.

      50%

    • D.

      75%

    • E.

      25%

    Correct Answer
    B. 100%
    Explanation
    When plants with red flowers are crossed with plants with white flowers, all of the offspring will have pink flowers. This is because the red flowers are homozygous for the dominant allele, while the white flowers are homozygous for the recessive allele. The heterozygous offspring will inherit one copy of the dominant allele from the red flower parent and one copy of the recessive allele from the white flower parent, resulting in pink flowers. Therefore, the proportion of offspring with pink flowers is 100%.

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  • 24. 

    Tallness (T) in snapdragons is dominant to dwarfness (t), while red (R) flower color is dominant to white (r). The heterozygous condition results in pink (Rr) flower color. A dwarf, red snapdragon is crossed with a plant homozygous for tallness and white flowers. What are the genotype and phenotype of the F1 individuals?

    • A.

      TtRr–dwarf and pink

    • B.

      TTRR–tall and red

    • C.

      Ttrr–dwarf and white

    • D.

      TtRr–tall and red

    • E.

      TtRr–tall and pink

    Correct Answer
    E. TtRr–tall and pink
    Explanation
    The F1 individuals will have the genotype TtRr, which means they are heterozygous for both tallness and flower color. The phenotype of the F1 individuals will be tall and pink, as the dominant traits for both tallness and red flower color are expressed in the heterozygous condition.

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  • 25. 

    Skin color in a certain species of fish is inherited via a single gene with four different alleles. How many different types of gametes would be possible in this system?

    • A.

      4

    • B.

      16

    • C.

      8

    • D.

      2

    • E.

      1

    Correct Answer
    A. 4
    Explanation
    In this system, there are four different alleles for the gene that determines skin color in the fish species. Each gamete contains only one allele, so the number of different types of gametes would be equal to the number of alleles. Therefore, there would be four different types of gametes possible in this system.

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  • 26. 

    When a disease is said to have a multifactorial basis, it means that

    • A.

      Both genetic and environmental factors contribute to the disease.

    • B.

      It has many different symptoms.

    • C.

      It is caused by a gene with a large number of alleles.

    • D.

      It tends to skip a generation.

    • E.

      It affects a large number of people.

    Correct Answer
    A. Both genetic and environmental factors contribute to the disease.
    Explanation
    When a disease is said to have a multifactorial basis, it means that both genetic and environmental factors contribute to the disease. This implies that the development and occurrence of the disease are influenced by a combination of genetic predisposition and external factors such as lifestyle, diet, exposure to toxins, and other environmental influences. The interaction between these factors determines the likelihood and severity of the disease. This concept highlights the complex nature of diseases and the need to consider multiple factors in understanding their causes and developing effective prevention and treatment strategies.

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  • 27. 

    People with sickle-cell trait

    • A.

      Have increased resistance to malaria.

    • B.

      Produce normal and abnormal hemoglobin.

    • C.

      Are usually healthy.

    • D.

      Are heterozygous for the sickle-cell allele.

    • E.

      All of the above

    Correct Answer
    E. All of the above
    Explanation
    People with sickle-cell trait have increased resistance to malaria because the abnormal hemoglobin produced by individuals with the sickle-cell allele makes it difficult for the malaria parasite to survive in their red blood cells. These individuals also produce normal and abnormal hemoglobin, as they have one normal allele and one sickle-cell allele. Despite having the sickle-cell allele, people with sickle-cell trait are usually healthy because they have enough normal hemoglobin to prevent the symptoms of sickle cell disease. Therefore, the correct answer is "all of the above."

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  • 28. 

    An ideal procedure for foetal testing in humans would have which of the following features?

    • A.

      A procedure that could test for the carrier status of the foetus

    • B.

      Lowest risk procedure that would provide the most reliable information

    • C.

      The procedure that can test for the greatest number of traits at once

    • D.

      A procedure that provides a 3D image of the foetus

    • E.

      The procedure that can be performed at the earliest time in the pregnancy

    Correct Answer
    B. Lowest risk procedure that would provide the most reliable information
    Explanation
    The ideal procedure for fetal testing in humans would be the one that has the lowest risk while still providing the most reliable information. This means that it should have minimal potential harm to the mother and the fetus, while also being accurate and providing valuable information about the health and development of the fetus. This balance between low risk and reliable information is crucial in ensuring the safety and well-being of both the mother and the unborn child.

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  • 29. 

    A scientist discovers a DNA-based test for the allele of a particular gene. This and only this allele, if homozygous, produces an effect that results in death at or about the time of birth. Of the following, which is the best use of this discovery?

    • A.

      To follow the segregation of the allele during meiosis

    • B.

      To introduce a normal allele into deficient newborns

    • C.

      To design a test for identifying heterozygous carriers of the allele

    • D.

      To test school-age children for the disorder

    • E.

      To screen all newborns of an at-risk population

    Correct Answer
    C. To design a test for identifying heterozygous carriers of the allele
    Explanation
    The best use of the DNA-based test for the allele of a particular gene that causes death at or about the time of birth when homozygous is to design a test for identifying heterozygous carriers of the allele. This is because identifying carriers of the allele can help in genetic counseling and family planning, allowing individuals with a higher risk of passing on the allele to make informed decisions about having children. Additionally, identifying carriers can also aid in early detection and intervention for any potential health issues related to the allele.

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  • 30. 

    An obstetrician knows that one of her patients is a pregnant woman whose fetus is at risk for a serious disorder that is detectable biochemically in foetal cells. The obstetrician would most reasonably offer which of the following procedures to her patient?

    • A.

      Amniocentesis

    • B.

      Ultrasound imaging

    • C.

      X-ray

    • D.

      Foetoscopy

    • E.

      CVS

    Correct Answer
    A. Amniocentesis
    Explanation
    Amniocentesis is the most reasonable procedure to offer to the patient because it involves collecting a sample of amniotic fluid, which contains fetal cells that can be analyzed for biochemical abnormalities. This procedure is commonly used to detect genetic disorders and chromosomal abnormalities in the fetus. Ultrasound imaging, X-ray, foetoscopy, and CVS (chorionic villus sampling) may also provide information about the fetus, but they are not specifically designed to detect biochemical disorders.

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  • 31. 

    The frequency of heterozygosity for the sickle cell anemia allele is unusually high, presumably because this reduces the frequency of malaria. Such a relationship is related to which of the following?

    • A.

      The malarial parasite changing the allele

    • B.

      Mendel's law of segregation

    • C.

      Darwin's observations of competition

    • D.

      Mendel's law of independent assortment

    • E.

      Darwin's explanation of natural selection

    Correct Answer
    E. Darwin's explanation of natural selection
    Explanation
    Darwin's explanation of natural selection suggests that the frequency of heterozygosity for the sickle cell anemia allele is unusually high because it reduces the frequency of malaria. This is because individuals with the sickle cell trait are less likely to contract severe malaria, resulting in a higher survival rate and reproductive success for those individuals. Over time, natural selection favors the sickle cell allele due to its beneficial effects in regions where malaria is prevalent.

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  • 32. 

    Cystic fibrosis (CF) is a Mendelian disorder in the human population that is inherited as a recessive. Two normal parents have two children with CF. The probability of their next child being normal for this characteristic is which of the following?

    • A.

      1/2

    • B.

      1/4

    • C.

      3/4

    • D.

      0

    • E.

      1/8

    Correct Answer
    B. 1/4
    Explanation
    In this scenario, both parents are carriers of the CF gene but do not have the disorder themselves. This means that they each have one normal allele and one CF allele. When they have children, there is a 1/4 chance that both parents will pass on their CF allele, resulting in a child with CF. However, there is also a 1/4 chance that both parents will pass on their normal allele, resulting in a child without CF. Therefore, the probability of their next child being normal for this characteristic is 1/4.

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  • 33. 

    Phenylketonuria (PKU) is a recessive human disorder in which an individual cannot appropriately metabolise a particular amino acid. This amino acid is not otherwise produced by humans. Therefore the most efficient and effective treatment is which of the following?

    • A.

      Feed them the substrate that can be metabolised into this amino acid.

    • B.

      Transfuse the patients with blood from unaffected donors.

    • C.

      Feed the patients the missing enzymes in a regular cycle, i.e., twice per week.

    • D.

      Regulate the diet of the affected persons to severely limit the uptake of the amino acid.

    Correct Answer
    D. Regulate the diet of the affected persons to severely limit the uptake of the amino acid.
    Explanation
    Phenylketonuria (PKU) is a disorder in which the individual cannot metabolize a specific amino acid. Since this amino acid is not produced by humans, the most efficient and effective treatment is to regulate the diet of the affected individuals to severely limit the intake of the amino acid. By controlling their diet and avoiding foods that contain this amino acid, the individuals can prevent the buildup of harmful substances and manage the symptoms of PKU. This treatment approach is more feasible and practical compared to providing the missing enzymes or transfusing blood from unaffected donors.

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  • 34. 

    Hutchinson-Gilford progeria is an exceedingly rare human genetic disorder in which there is very early senility, and death, usually of coronary artery disease, at an average age of approximately 13. Patients, who look very old even as children, do not live to reproduce. Which of the following represents the most likely assumption?

    • A.

      All cases must occur in relatives; therefore, there must be only one mutant allele.

    • B.

      Each patient will have had at least one affected family member in a previous generation.

    • C.

      Successive generations of a family will continue to have more and more cases over time.

    • D.

      The disorder may be due to mutation in a single protein-coding gene.

    • E.

      The disease is autosomal dominant.

    Correct Answer
    D. The disorder may be due to mutation in a single protein-coding gene.
    Explanation
    The most likely assumption is that the disorder may be due to a mutation in a single protein-coding gene. This is because the disorder is described as a genetic disorder, and the fact that all patients have the condition suggests a common genetic cause. A mutation in a single gene can lead to the manifestation of the disorder in each patient.

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  • 35. 

    A pedigree analysis for a given disorder's occurrence in a family shows that, although both parents of an affected child are normal, each of the parents has had affected relatives with the same condition. The disorder is then which of the following?

    • A.

      Maternally inherited

    • B.

      Cominant

    • C.

      Incompletely dominant

    • D.

      Recessive

    • E.

      A new mutation

    Correct Answer
    D. Recessive
    Explanation
    Based on the pedigree analysis, it can be concluded that the disorder is recessive. This is because both parents of the affected child are normal, indicating that they are carriers of the recessive allele for the disorder. Additionally, the presence of affected relatives in both parents' families suggests that the disorder is inherited in a recessive manner.

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  • 36. 

    One of two major forms of a human condition called neurofibromatosis (NF 1) is inherited as a dominant, although it may be either mildly to very severely expressed. If a young child is the first in her family to be diagnosed, which of the following is the best explanation?

    • A.

      The child has a different allele of the gene than the parents.

    • B.

      The condition skipped a generation in the family.

    • C.

      One of the parents has very mild expression of the gene.

    • D.

      The mother carries the gene but does not express it at all.

    Correct Answer
    C. One of the parents has very mild expression of the gene.
    Explanation
    If a young child is the first in her family to be diagnosed with neurofibromatosis (NF 1), the best explanation is that one of the parents has a very mild expression of the gene. This means that the parent carries the gene but does not show any symptoms or only has very mild symptoms. As a result, the child may inherit a more severe form of the condition due to the combination of the mild expression of the gene from one parent and the possibility of a different allele of the gene from the other parent.

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Our quizzes are rigorously reviewed, monitored and continuously updated by our expert board to maintain accuracy, relevance, and timeliness.

  • Current Version
  • Mar 21, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Jun 08, 2011
    Quiz Created by
    Sparkles12345
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