Unit 3 Chapter 1 (1st Secondary) Biology

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Unit 3 Chapter 1 (1st Secondary) Biology - Quiz


Questions and Answers
  • 1. 

    In a certain strain of animals, the gene of black colour dominates the gene of white one. What is the result of mating a hybrid animal with a recessive one?

    • A.

      50% black : 50% white

    • B.

      75% black : 25% white

    • C.

      25% black : 75% white

    • D.

      Zero % black : 100% white

    Correct Answer
    A. 50% black : 50% white
    Explanation
    When a hybrid animal with a dominant black gene mates with a recessive white gene animal, the offspring will inherit one black gene and one white gene, resulting in a 50% chance of being black and a 50% chance of being white.

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  • 2. 

     The percentage of gametes with a genotype (Ab) produced from  Aabb is

    • A.

      50%

    • B.

      75%

    • C.

      25%

    • D.

      100%

    Correct Answer
    A. 50%
    Explanation
    When crossing Aabb (heterozygous for both genes) with itself, the possible gametes that can be produced are Ab, aB, AB, and ab. Since the genotype Aabb only produces one type of gamete, which is Ab, the percentage of gametes with the genotype (Ab) produced from Aabb is 50%.

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  • 3. 

    The number of different gametes that can be produced in a male, based on independent assortment, equals __.

    • A.

      2

    • B.

      23

    • C.

      223

    • D.

      26

    Correct Answer
    C. 223
    Explanation
    Based on independent assortment, the number of different gametes that can be produced in a male equals 2^3, which is equal to 8. This is because each gene pair segregates independently during meiosis, resulting in 2 possible outcomes for each gene pair. Since there are 3 gene pairs involved, the total number of different gametes that can be produced is 2^3, which equals 8. Therefore, the correct answer is 8.

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  • 4. 

    If the percentage of the offspring with a genotype AABB is 25% so the parents are 

    • A.

      AABB x aabb

    • B.

      AABB x AaBb

    • C.

      Aabb x aabb

    • D.

      AaBB x AABB

    Correct Answer
    B. AABB x AaBb
    Explanation
    The percentage of offspring with a genotype AABB can only occur if one parent has the genotype AABB and the other parent has the genotype AaBb. This is because AABB is a homozygous dominant genotype, while AaBb is a heterozygous genotype. When these two genotypes are crossed, there is a 25% chance of producing offspring with the AABB genotype.

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  • 5. 

    If crossed with a green, wrinkled, seeded pea plant, which of the following genotypes will give all possible phenotypes distributed equally in their offspring?

    • A.

      YySS

    • B.

      YySs

    • C.

      Yyss

    • D.

      YySs

    Correct Answer
    B. YySs
    Explanation
    When crossed with a green, wrinkled, seeded pea plant, the genotype YySs will give all possible phenotypes distributed equally in their offspring. This is because the genotype YySs has a combination of dominant and recessive alleles for both traits (yellow vs. green and smooth vs. wrinkled), allowing for the expression of all possible phenotypes in the offspring.

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  • 6. 

    Mendel studied the inheritance of 7 traits in pea plants and did not come across any sort of linkage. Which one of Mendel’s laws of inheritance would have been completely different if Mendel observed linkage between these genes?

    • A.

      The law of segregation of genetic factors

    • B.

      The law of complete dominance

    • C.

      The law of independent assortment

    • D.

      None of the answers is correct.

    Correct Answer
    C. The law of independent assortment
    Explanation
    If Mendel had observed linkage between the genes for the 7 traits in pea plants, it would have contradicted the law of independent assortment. This law states that during the formation of gametes, the alleles for different traits segregate independently of one another. In other words, the inheritance of one trait is not dependent on the inheritance of another trait. If there was linkage between the genes, it would mean that certain traits are inherited together more frequently than would be expected by chance, which would go against the principle of independent assortment.

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  • 7. 

    Which one of the following is an acquired characteristic?

    • A.

      Being a super taster

    • B.

      Hair colour

    • C.

       Eye colour

    • D.

      Being good at football

    Correct Answer
    D. Being good at football
    Explanation
    Being good at football is an acquired characteristic because it is a skill that can be learned and developed through practice, training, and experience. It is not determined by genetics or inherited traits like hair color or eye color. Super taster refers to an individual with heightened taste sensitivity, but it is not something that can be acquired. Therefore, being good at football is the only option that fits the definition of an acquired characteristic.

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  • 8. 

    What are (A) and (B) in the following diagram?

    • A.

      (A) meiosis, (B) mitosis

    • B.

      (A) mitosis, (B) fertilization 

    • C.

      (A) mitosis, (B) meiosis

    • D.

      (A) meiosis, (B) fertilization

    Correct Answer
    D. (A) meiosis, (B) fertilization
    Explanation
    In the given diagram, (A) represents meiosis and (B) represents fertilization. Meiosis is the process of cell division that occurs in reproductive cells to produce gametes with half the number of chromosomes. Fertilization is the fusion of male and female gametes to form a zygote with a full set of chromosomes. Therefore, (A) meiosis and (B) fertilization are the correct answers based on the descriptions provided.

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  • 9. 

    When crossing a male with the genotype aaBb and a female with the genotype AABb, which of the following is a possible genotype for their offspring?

    • A.

        Aabb

    • B.

        aabb

    • C.

        AABb

    • D.

         aaBB

    Correct Answer
    A.   Aabb
    Explanation
    When crossing a male with the genotype aaBb and a female with the genotype AABb, their offspring can have the genotype Aabb. This is possible because the male contributes the allele "a" and "b" while the female contributes the allele "A" and "b". This results in the offspring having the genotype Aabb.

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  • 10. 

    Karyotype of a male human differs from that of the female in the

    • A.

      Number of sex chromosomes

    • B.

      Type of sex chromosomes  

    • C.

      Arrangement of autosomes

    • D.

      Number of the autosome pairs

    Correct Answer
    B. Type of sex chromosomes  
    Explanation
    The karyotype of a male human differs from that of a female in the type of sex chromosomes. Males have one X and one Y chromosome, while females have two X chromosomes. This difference in sex chromosomes determines the biological sex of an individual. The arrangement of autosomes and the number of autosome pairs are the same in both males and females.

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  • 11. 

    The albinism in human is a recessive trait that represented by (aa). What is the result of mating a man and a woman both of them are a normal hybrid for this trait?

    • A.

      25% Albino

    • B.

      100% normal

    • C.

      50% Albino

    • D.

      50% normal

    Correct Answer
    A. 25% Albino
    Explanation
    When a man and a woman who are both normal hybrids for albinism mate, they each have one copy of the normal allele (Aa) and one copy of the albino allele (aa). The albino allele is recessive, meaning that it is only expressed when an individual has two copies of it (aa). Therefore, there is a 25% chance that both parents will pass on their albino allele to their offspring, resulting in the offspring being albino.

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  • 12. 

    Which of the following crosses will produce offspring which is composed only of the same genotypes of parents with ratio 1∶1? (knowing that the two genes A and B are not linked)

    • A.

        AABb X AAbb

    • B.

        AAbb X aaBb

    • C.

        aaBB X AABb

    • D.

        AaBb X AABB

    Correct Answer
    A.   AABb X AAbb
    Explanation
    The cross AABb X AAbb will produce offspring with the same genotypes as the parents in a 1:1 ratio. This is because both parents have different genotypes for the same two genes (A and B), and the offspring will inherit one allele from each parent for each gene. In this cross, half of the offspring will inherit the A and B alleles from the AABb parent, and the other half will inherit the a and b alleles from the AAbb parent, resulting in a 1:1 ratio of genotypes.

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  • 13. 

    Which of the following chromosomes has the largest size in the human karyotype?

    • A.

      Chromosome (22)

    • B.

      Chromosome (Y)

    • C.

      Chromosome (9)

    • D.

      Chromosome (X)

    Correct Answer
    D. Chromosome (X)
    Explanation
    Chromosome (X) has the largest size in the human karyotype because it contains a large amount of genetic material. It is one of the two sex chromosomes, with the other being the smaller Y chromosome. The X chromosome carries numerous genes that are essential for the development and functioning of various traits and characteristics in both males and females.

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  • 14. 

    The figure represents the karyotype of a(an) -----------

    • A.

      Human male

    • B.

      Human female

    • C.

      Sperm

    • D.

      Ovum

    Correct Answer
    A. Human male
    Explanation
    The figure represents the karyotype of a human male because the karyotype shows the chromosomes present in an individual's cells. In this case, the karyotype shows the typical 46 chromosomes found in human males, including one X and one Y chromosome, which determine male sex.

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  • 15. 

    All of the following are possible gametes which can be produced during the cross between AaBB and AAbb except for ..........

    • A.

        AB

    • B.

        Ab

    • C.

        aB

    • D.

        ab

    Correct Answer
    D.   ab
    Explanation
    During the cross between AaBB and AAbb, the possible gametes that can be produced are AB, Ab, aB, and ab. However, the gamete "ab" cannot be produced because both parents have at least one dominant allele for the B gene (AaBB and AAbb). Therefore, the correct answer is "ab".

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  • 16. 

    If the number of chromosomes in a human skin cells is 23 pairs, so the number of chromosomes in the sperm is

    • A.

      23 pairs

    • B.

      23

    • C.

      46 pairs

    • D.

      46

    Correct Answer
    B. 23
    Explanation
    The number of chromosomes in a human skin cell is 23 pairs, meaning there are a total of 46 chromosomes. However, when it comes to sperm cells, they are haploid, meaning they only contain one set of chromosomes. Therefore, the number of chromosomes in a sperm cell is 23.

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  • 17. 

    The greatest number of chromosomes is found in the -------- cells

    • A.

      Human

    • B.

      Dog

    • C.

      Cat

    • D.

      Frog

    Correct Answer
    B. Dog
    Explanation
    The correct answer is Dog because dogs typically have a greater number of chromosomes compared to humans, cats, and frogs. Chromosomes are thread-like structures found in the nucleus of cells that carry genetic information. Dogs have a diploid number of 78 chromosomes, while humans have 46, cats have 38, and frogs have around 26. Therefore, the greatest number of chromosomes is found in dog cells.

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  • 18. 

    In the human pedigree shown below, the daughter indicated by the red circle (II-1) has a form of deafness determined by a recessive allele. What is the probability that the phenotypically normal son (II-3) is heterozygous for the gene?

    • A.

      100%

    • B.

      50%

    • C.

      Less than 50%

    • D.

      More than 50%

    Correct Answer
    D. More than 50%
    Explanation
    The daughter (II-1) has a form of deafness determined by a recessive allele, indicating that she must be homozygous recessive (dd). Since the son (II-3) is phenotypically normal, he must have at least one dominant allele (D_). The only way for him to be phenotypically normal and carry the recessive allele is if he is heterozygous (Dd). Therefore, the probability that the son (II-3) is heterozygous for the gene is more than 50%.

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  • 19. 

    If two Pea plants carry purple flowers (Rr) were crossed, so the percentage of appearance of white flowers in the resulted generation is

    • A.

      25%

    • B.

      Zero %

    • C.

      75%

    • D.

      100%

    Correct Answer
    A. 25%
    Explanation
    When two pea plants carrying purple flowers (Rr) are crossed, the resulting generation will have a genotype ratio of 1 RR : 2 Rr : 1 rr. The rr genotype represents the white flower trait. Since only one out of the four possible genotypes is rr, the percentage of appearance of white flowers in the resulting generation is 25%.

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  • 20. 

    The least number of chromosomes is found in the ------ cells

    • A.

      Wheat

    • B.

      Onion

    • C.

      Sweet potato

    • D.

      Pea

    Correct Answer
    D. Pea
    Explanation
    Pea plants have the least number of chromosomes among the given options. Chromosomes are thread-like structures found in the nucleus of cells that contain genetic information. Pea plants have a relatively small genome and a diploid number of 14 chromosomes. In comparison, wheat has 42 chromosomes, onion has 16 chromosomes, and sweet potato has 90 chromosomes. Therefore, pea cells have the least number of chromosomes.

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  • 21. 

    From the characters of the human sex chromosomes

    • A.

      They are the pair number 7

    • B.

      They are the pair number 23

    • C.

      They do not carry genes

    • D.

      They are autosomes

    Correct Answer
    B. They are the pair number 23
    Explanation
    The human sex chromosomes consist of a pair of chromosomes, known as the X and Y chromosomes. In males, the pair is designated as number 23, while in females, it is designated as pair number 7. This is because males have one X and one Y chromosome, while females have two X chromosomes. The designation of pair number 23 for the sex chromosomes helps to differentiate them from the autosomes, which are the remaining pairs of chromosomes in the human genome. Therefore, the correct answer is that the sex chromosomes are the pair number 23.

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  • 22. 

    The best method to determine the genotype of a dominant individual is by crossing it with the ---

    • A.

      Hybrid

    • B.

      Recessive

    • C.

      Pure dominant

    • D.

      Same genotype

    Correct Answer
    B. Recessive
    Explanation
    When determining the genotype of a dominant individual, crossing it with a recessive individual is the best method. This is because if the dominant individual is homozygous dominant (pure dominant), all the offspring will also exhibit the dominant trait. However, if the dominant individual is heterozygous, some of the offspring will exhibit the recessive trait, revealing that the dominant individual carries one copy of the recessive allele. By crossing with a recessive individual, the presence or absence of the recessive trait in the offspring can help determine the genotype of the dominant individual.

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  • 23. 

    Genes of formation of the root system in plants is affected inversely by the amount of humidity in the soil. If you know that “Brooklime plant” has very short roots. So in which environment does this plant live?

    • A.

      Desert

    • B.

      Clay

    • C.

      Sand

    • D.

      Water

    Correct Answer
    D. Water
    Explanation
    The given information states that the genes responsible for the formation of the root system in plants are affected inversely by the amount of humidity in the soil. Since the "Brooklime plant" has very short roots, it suggests that this plant lives in an environment with high humidity, such as water.

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  • 24. 

    The gene is formed of a sequence of

    • A.

      DNA

    • B.

      Nucleotides

    • C.

      Amino acids

    • D.

      Chromosomes

    Correct Answer
    B. Nucleotides
    Explanation
    A gene is formed of a sequence of nucleotides. Nucleotides are the building blocks of DNA, which carries the genetic information in an organism. Genes are specific sections of DNA that contain the instructions for making proteins. These instructions are encoded in the sequence of nucleotides. Each nucleotide consists of a sugar molecule, a phosphate group, and a nitrogenous base. The sequence of nucleotides determines the sequence of amino acids in a protein, which ultimately determines the structure and function of the protein. Therefore, nucleotides are the correct answer as they are the fundamental units that make up genes.

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  • 25. 

    When a pure purple flowered Pea plant was crossed with another one of white flowers, so the resulted generation will be

    • A.

      100% purple

    • B.

      75% purple : 25% white

    • C.

      50% purple : 50% white

    • D.

      100% white

    Correct Answer
    A. 100% purple
    Explanation
    When a pure purple flowered Pea plant is crossed with another one of white flowers, the resulting generation will be 100% purple. This is because the purple flower trait is dominant over the white flower trait. Therefore, all offspring from this cross will inherit the purple flower trait from the pure purple flowered parent.

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  • 26. 

    The two scientists that had reached to the principles of the chromosomal theory are

    • A.

      Urey and Miller

    • B.

      Watson and Crick

    • C.

      Mendel and Morgan

    • D.

      Sutton and Boveri

    Correct Answer
    D. Sutton and Boveri
    Explanation
    Sutton and Boveri are the correct answer because they were the two scientists who independently proposed the chromosomal theory of inheritance. Sutton developed the theory based on his observations of grasshopper chromosomes, while Boveri made similar discoveries studying sea urchin embryos. Their work laid the foundation for understanding how genetic information is transmitted through chromosomes during sexual reproduction.

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  • 27. 

    A tall plant with red flowers was crossed with another one having the same phenotype. If 56.25% of the offspring were parental and the rest were recombinant. So the genotypes of the parents should be -----

    • A.

      TTRR X TtRr

    • B.

      TtRr X TtRr

    • C.

      TtRR X TTRr

    • D.

      TTrr X ttRR

    Correct Answer
    B. TtRr X TtRr
    Explanation
    The correct answer is TtRr X TtRr. This is because if 56.25% of the offspring were parental, it indicates that the traits from both parents were inherited without any recombination. In this case, the parents must have the same phenotype, which is a tall plant with red flowers. The genotype TtRr represents a heterozygous combination for both traits, allowing for the expression of both tallness and red flowers. Therefore, crossing two plants with the genotype TtRr would result in 56.25% of the offspring being parental and the remaining being recombinant.

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  • 28. 

    Which of the following is true about chromosomes?

    • A.

      All cells of different living organisms have the same number of chromosomes

    • B.

      Number of chromosomes in cells of the same species is constant

    • C.

      Number of chromosomes in human males differs from that in human females

    • D.

      Number of chromosomes in the liver cells differs from that in the pancreatic cells

    Correct Answer
    B. Number of chromosomes in cells of the same species is constant
    Explanation
    The correct answer is that the number of chromosomes in cells of the same species is constant. This means that all individuals of a particular species will have the same number of chromosomes in their cells. This is a characteristic feature of each species and helps to define their genetic makeup. The number of chromosomes can vary between different species, but within a species, it remains constant.

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  • 29. 

    The ratio of segregation in the 2nd generation in the complete dominance according to Mendel's 1st law is

    • A.

      3:0

    • B.

      1:1

    • C.

      3: 1

    • D.

      1:2:1

    Correct Answer
    C. 3: 1
    Explanation
    According to Mendel's 1st law of complete dominance, the ratio of segregation in the 2nd generation is 3:1. This means that for every three individuals with a dominant trait, there will be one individual with a recessive trait. This ratio is consistent with Mendel's observations and his understanding of how traits are inherited.

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  • 30. 

    The ratio of the 2nd generation in the law of independent assortment is

    • A.

      3:1

    • B.

      1:1

    • C.

      2:1

    • D.

      9:3:3:1

    Correct Answer
    D. 9:3:3:1
    Explanation
    The correct answer is 9:3:3:1. In the law of independent assortment, the ratio of the 2nd generation is determined by the combination of alleles from the parents. In this case, the ratio indicates that for every 9 individuals with a certain combination of alleles, there will be 3 individuals with a different combination of alleles, and another 3 individuals with yet another combination of alleles, while only 1 individual will have a different combination of alleles. This ratio suggests that there is a certain pattern in the inheritance of traits from the parents to the offspring.

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  • 31. 

    A crossing took place between a plant (BB) and another one (bb) , the  result was the production of 150 new plants. so the number of plants which carries the genotype (Bb) was

    • A.

      30

    • B.

      150

    • C.

      75

    • D.

      50

    Correct Answer
    B. 150
    Explanation
    When a crossing occurs between a plant with genotype BB and another plant with genotype bb, the resulting offspring will all have genotype Bb. Since the question states that 150 new plants were produced, it can be inferred that all of these plants carry the genotype Bb. Therefore, the correct answer is 150.

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  • 32. 

    A male cat of a genotype (Aa) is crossed to a female one having the same genotype, so the possibility of producing cats with a genotupe (AA) is

    • A.

      25%

    • B.

      50%

    • C.

      75%

    • D.

      100%

    Correct Answer
    A. 25%
    Explanation
    When a male cat with genotype (Aa) is crossed with a female cat with the same genotype (Aa), the possible genotypes of their offspring are AA, Aa, and aa. Since the genotype AA is only possible when both parents contribute the dominant allele A, and each parent has a 50% chance of passing on the dominant allele, the probability of producing cats with genotype AA is 50%. Therefore, the given answer of 25% is incorrect.

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  • 33. 

    The genotype GgRR can produce the following gametes

    • A.

      Gg and Rr

    • B.

      GG and Rr

    • C.

      Gr and gR

    • D.

      GR and gR

    Correct Answer
    D. GR and gR
    Explanation
    The genotype GgRR consists of two genes, G and R, with one dominant allele (G) and one recessive allele (g) for the G gene, and two dominant alleles (R) for the R gene. During gamete formation, the alleles segregate independently, meaning that each gamete will receive one allele for each gene. Therefore, the possible gametes that can be produced are GR (with a dominant G allele and a dominant R allele) and gR (with a recessive g allele and a dominant R allele).

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  • 34. 

    Which of the following is the true ratio for the appearance of red flower in Antirrhinum plant that result from the crossing of a plant with purple flowers and another with white flowers?

    • A.

      75 %

    • B.

      25 %

    • C.

      0 %

    • D.

      50 %

    Correct Answer
    C. 0 %
    Explanation
    When a plant with purple flowers is crossed with another plant with white flowers, the resulting offspring will have pink flowers. This is because the purple color is dominant and the white color is recessive. Therefore, there will be no appearance of red flowers in this crossing, resulting in a ratio of 0%.

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  • 35. 

    If you crossed two heterozygous plants, how many of the offspring will also be heterozygous?

    • A.

      All

    • B.

      Half

    • C.

      3/4

    • D.

      1/4

    Correct Answer
    B. Half
    Explanation
    If you cross two heterozygous plants, it means that both parents have one dominant and one recessive allele for a particular trait. When these plants reproduce, each parent can pass on either the dominant or the recessive allele to their offspring. Since both parents are heterozygous, there is a 50% chance that each offspring will receive the dominant allele and a 50% chance that they will receive the recessive allele. Therefore, half of the offspring will also be heterozygous.

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  • 36. 

    A pure character is the character which has 

    • A.

      Two different genes

    • B.

      Two genes on two different pairs of chromosomes

    • C.

      Two similar genes

    • D.

      Different alleles

    Correct Answer
    C. Two similar genes
    Explanation
    A pure character refers to a character that has two similar genes. This means that the genes on both pairs of chromosomes are identical or have the same alleles. This is in contrast to a character with two different genes, where the genes on the two pairs of chromosomes are different or have different alleles.

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  • 37. 

    Choose the correct statement regarding the chromosomal theory from the following:

    • A.

      Only sex chromosomes are found as homologous pairs in somatic cells and gametes.

    • B.

      The segregation of each pair of chromosomes into gametes is independent.

    • C.

      After the fertilization of somatic cells, half of the number of chromosomes is lost to be 2n

    • D.

      Chromosomes are found in gametes as homologous pairs. 

    Correct Answer
    B. The segregation of each pair of chromosomes into gametes is independent.
    Explanation
    The correct statement regarding the chromosomal theory is that the segregation of each pair of chromosomes into gametes is independent. This means that during the formation of gametes, the two chromosomes of each homologous pair can separate randomly, resulting in different combinations of chromosomes in the gametes. This principle of independent assortment is one of the key components of Mendel's laws of inheritance and is supported by the observation of chromosomes during meiosis.

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  • 38. 

    A pedigree is shown below for a disease (the shaded members) that is autosomal dominant. What is the genotype of the Generation I ? (circles represent females and squares represent males) 

    • A.

      AA, aa 

    • B.

      Aa, aa

    • C.

      Aa, AA 

    • D.

      Aa, Aa.

    Correct Answer
    B. Aa, aa
    Explanation
    In an autosomal dominant disease, the presence of the disease is indicated by at least one affected parent. In the given pedigree, the shaded members represent individuals affected by the disease. Generation I consists of two individuals, one male (square) and one female (circle). The female is affected by the disease, which means she must have inherited the disease-causing allele from one of her parents. Since the disease is autosomal dominant, the affected female (Generation I) must have inherited at least one dominant disease-causing allele (Aa) from one of her parents. The unaffected male (Generation I) does not carry the disease-causing allele, so his genotype is aa. Therefore, the genotype of Generation I is Aa, aa.

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  • 39. 

    A dihybrid cross (AaBb x AaBb) will result in what offspring ratio? 

    • A.

      9:3:3:1

    • B.

      9:7

    • C.

      3:1

    • D.

      9:3:3:1 or  9:7

    Correct Answer
    D. 9:3:3:1 or  9:7
    Explanation
    A dihybrid cross involves the crossing of two individuals that are heterozygous for two different traits. The resulting offspring ratio of 9:3:3:1 indicates that 9 out of 16 offspring will have both dominant traits, 3 out of 16 will have one dominant and one recessive trait, 3 out of 16 will have the other dominant trait and one recessive trait, and 1 out of 16 will have both recessive traits. The alternative answer of 9:7 suggests that 9 out of 16 offspring will have at least one dominant trait, while 7 out of 16 will have at least one recessive trait.

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  • 40. 

    A gene is a section of _____ that contains the instructions for making a particular type of _______.

    • A.

      DNA and protein

    • B.

      Nucleus and cytoplasm

    • C.

      DNA and chromosomes

    • D.

      Chromosomes and protein

    Correct Answer
    A. DNA and protein
    Explanation
    A gene is a section of DNA that contains the instructions for making a particular type of protein. DNA serves as the genetic material in living organisms and carries the genetic information needed for the development, functioning, and reproduction of cells. Proteins, on the other hand, are the building blocks of cells and perform various functions within the body. Therefore, the correct answer is DNA and protein.

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  • 41. 

    In a certain strain of dicot. plants, the gene (Y) for yellow seeds dominates (y) for green seeds. Also the gene (R) for red flowers dominates (r) for white flowers. In a dihybrid cross between two plants having the same genotype (YyRr) the resulting offspring are: 75% with yellow seeds and red flowers : 25% with green seeds and white flowers. what is your explanation?

    • A.

      (R) and (Y) are carried on the same chromosome, while (r) and (y) are carried on the homologous one.

    • B.

      (R) and (y) are carried on the same chromosome, while (r) and (Y) are carried on the homologous one.

    • C.

      (R) and (r) are carried on a pair of chromosomes, while (Y) and (y) are carried on another pair.

    • D.

      (R) and (Y) are carried on a pair of chromosomes while (r) and (y) are carried on another pair.

    Correct Answer
    A. (R) and (Y) are carried on the same chromosome, while (r) and (y) are carried on the homologous one.
    Explanation
    The correct answer is (R) and (Y) are carried on the same chromosome, while (r) and (y) are carried on the homologous one. This means that the genes for red flowers and yellow seeds are located on one chromosome, while the genes for white flowers and green seeds are located on the homologous chromosome. This explains why the offspring in the dihybrid cross have a 75% chance of having both yellow seeds and red flowers, as these traits are linked on the same chromosome. Similarly, there is a 25% chance of the offspring having both green seeds and white flowers, as these traits are also linked on the homologous chromosome.

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  • 42. 

    A plant that has purple flowers is crossed with one that has white flowers. The offspring were half white and half purple. What were the genotypes of the parents?

    • A.

      Pp X pp

    • B.

      Pp X Pp

    • C.

      PP X pp

    • D.

      PP X Pp

    Correct Answer
    A. Pp X pp
    Explanation
    In this scenario, the plant with purple flowers must have the genotype Pp, as it can produce both purple (PP) and white (pp) offspring. The plant with white flowers must have the genotype pp, as it can only produce white offspring. Therefore, when the plant with purple flowers (Pp) is crossed with the plant with white flowers (pp), the possible genotypes of the offspring are Pp (purple) and pp (white), resulting in half white and half purple offspring.

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  • 43. 

    Which of the following describes the sex-determining chromosome in humans?

    • A.

      Is arranged as number 8 in the karyotype

    • B.

      Carries genes for self-characters

    • C.

      Is passed only from father to son

    • D.

      It comes after the seventh pair in size

    Correct Answer
    C. Is passed only from father to son
    Explanation
    The sex-determining chromosome in humans is the Y chromosome, which is passed only from father to son. This is because the Y chromosome carries the genes that determine male sex characteristics, and it is not present in females. The Y chromosome is typically arranged as number 8 in the karyotype, and it is smaller in size than the seventh pair of chromosomes.

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  • 44. 

    Chromosomes are arranged descendingly in a karyotype according to 

    • A.

      The number of genes that they carry

    • B.

      The type of genes that they carry

    • C.

      Their size 

    • D.

      Their density

    Correct Answer
    C. Their size 
    Explanation
    Chromosomes are arranged descendingly in a karyotype according to their size. This means that the larger chromosomes are placed first, followed by the smaller ones. This arrangement allows for easier visualization and analysis of the chromosomes, as it provides a clear order based on their physical characteristics.

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  • 45. 

    If the genotype of a child is (bb) so the genotype of his parents should be

    • A.

      Bb x Bb

    • B.

      BB x bb

    • C.

      BB xBb

    • D.

      BB x BB

    Correct Answer
    A. Bb x Bb
    Explanation
    The genotype of a child is (bb), which indicates that the child has a homozygous recessive genotype. In order for a child to have a homozygous recessive genotype, both parents must contribute a recessive allele. Therefore, the genotype of the parents should be Bb x Bb, where each parent carries one dominant allele (B) and one recessive allele (b).

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  • 46. 

    Pea plants were used in Mendel’s experiments because ----------.

    • A.

      They were cheap

    • B.

      They had contrasting characters

    • C.

      They were available easily

    • D.

      All of the above

    Correct Answer
    D. All of the above
    Explanation
    Pea plants were used in Mendel's experiments because they were cheap, had contrasting characters, and were easily available. Mendel needed a large number of plants to conduct his experiments, and pea plants fit these criteria. Additionally, pea plants have easily observable and distinct traits, such as flower color and seed shape, which allowed Mendel to easily track and analyze inheritance patterns. Therefore, all of the given reasons are valid explanations for why pea plants were used in Mendel's experiments.

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  • 47. 

    If a plant with genotype AaBb is self-fertilized, the probability of getting AABB genotype will be -------(Knowing that A and B are not linked)

    • A.

      1/2

    • B.

      3/4

    • C.

      2/8

    • D.

      1/16

    Correct Answer
    D. 1/16
    Explanation
    When a plant with genotype AaBb is self-fertilized, the offspring will inherit one allele from each parent for each gene. Since A and B are not linked, the inheritance of one gene does not affect the inheritance of the other gene. Therefore, the probability of inheriting the AABB genotype is the product of the probabilities of inheriting AA and BB genotypes separately. The probability of inheriting AA genotype from Aa parent is 1/2, and the probability of inheriting BB genotype from Bb parent is also 1/2. Multiplying these probabilities gives 1/2 * 1/2 = 1/4. Since there are two genes involved, the probability of inheriting AABB genotype is 1/4 * 1/4 = 1/16.

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