Exams Prep Master
Genetics is the branch of science that deals with the study of how certain qualities or traits are passed from parents to their offspring as a result of changes in DNA sequence or genetic material. Gregor Mendel, the “father of genetics”, proposed Mendel’s laws of Inheritance, which include the law of dominance, the law of segregation, and the law of independent assortment. Based on his experiments and analyses on the pea plant, these laws explain the various characteristics of inheritance.
According to the NCERT syllabus, the unit on Genetic Principles and Molecular Processes covers the Basic Principles of Inheritance, Basic Processes, and Genetic Disorders. These provide some important MCQs from the examination point of view, which have been discussed in this article.
Ques. The tendency of an offspring to resemble its parent is known as:
- Variation
- Heredity
- Resemblance
- Inheritance
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Ans. Heredity
Explanation: Heredity is the passing on of traits such as the color of the hair or eyes, eye color, skin complexion, height, intelligence, and so on., from parents to offspring. It is also known as vertical transmission. Thus, based on these traits the offspring often resembles the parent.
Inheritance is the passing of genetic information from parent to child. The genetic information is passed to the offspring through the DNA (deoxyribonucleic acid) present in the sex cells. For example, genetic diseases such as hemophilia are transmitted through inheritance.
Variation is the degree to which the offspring differs from the parent in terms of their physiology, morphology, cytology, and behavioral traits. Such variation may be a result of reshuffling of gene/chromosomes, crossing over or recombination, or mutation and environmental effects.
Ques. The alternate form of a gene is known as
- Allele
- Alternate type
- Dominant character
- Genotype
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Ans. Allele
Explanation: Allele (derived from the Greek word ‘allos’ meaning ‘other’) refers to different varieties of a gene present in the chromosomes[4]. They are a pair of genes found on the same place of chromosomes raised by the mutation. Genotype refers to the complete set of genes that can be passed down to the offspring by the parent.
Ques. The genotypic ratio of a monohybrid cross is:
- 1:2:1
- 2:1:1
- 3:1
- 9:3:3:1
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Ans. 1:2:1
Explanation: A monohybrid cross between a pure tall plant (TT) with the pure dwarf plant (tt). In the F1 generation tall plants (Tt) are formed. When this plant is subjected to self-pollination, the F2 generation has 3 tall plants and 1 dwarf plant. The ratio between tall and dwarf plants is 3:1. The genotype of 1 plant is TT, 2 plants are Tt, and1 plant with tt. Therefore, the genotypic ratio is 1:2:1.
Representation of the genotypic ratio of a monohybrid cross
Ques. The term ‘gene’ refers to:
- A portion of the RNA
- A portion of the DNA
- A sequence of amnio acids in protein
- A linkage group
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Ans. A portion of the DNA
Explanation: Genes are the structural and functional unit of heredity. They are a portion of the DNA that are located inside the chromosomes. Every gene contains a particular set of instructions for a particular function or protein-coding.
Ques. The DNA is composed of:
- Protein
- Lipid
- Nucleic Acid
- All of the above
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Ans. Nucleic Acid
Explanation: Deoxyribonucleic acid (DNA) is a nucleic acid and is thus made up of nucleotides. Each nucleotide comprises a phosphate group, a nitrogenous base and ribose sugar.
Ques. Which of the following is a chromosomal disorder that causes undeveloped female characteristics and is sterile?
- Down’s syndrome
- Klinefelter’s syndrome
- Turner’s syndrome
- Phenylketonuria
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Ans. Turner’s syndrome
Explanation: Turner’s syndrome is a chromosomal disorder caused by the absence of one X chromosome i.e., the number of chromosomes is 45. Thus, females with this disorder have undeveloped feminine characteristics. In contrast, Klinefelter’s syndrome occurs when there is the presence of one extra X chromosome. This results in the development of feminine characters in males.
Ques. The other term for genetic engineering is
- DNA fingerprinting
- Gene therapy
- Recombinant DNA technology
- DNA editing
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Ans. Recombinant DNA technology
Explanation: Genetic engineering is also called recombinant DNA technology as it involves the set of techniques that are used to cut up and join together genetic material, especially DNA from different biological species, and introduce the resulting hybrid DNA into an organism in order to form new combinations of heritable genetic material.
Ques. Which of the following statements is false for the Watson and Crick model of DNA?
- The helix has a deep, wide major groove and a shallow, narrow, minor groove.
- The two strands run antiparallel.
- A complete turn occurs in every 34A.
- Adenine can bind to thymine by 3 hydrogen bonds and guanine can bind to cytosine by 2 hydrogen bonds.
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Ans. Adenine can bind to thymine by 3 hydrogen bonds and guanine can bind to cytosine by 2 hydrogen bonds.
Explanation: According to the Watson and Crick Model, the DNA molecule comprises two stands bonded to each other by hydrogen bonds and are twisted to form a helix. Further, Adenine (A) can bind to thymine (T) by 2 hydrogen bonds and guanine (G) can bind to cytosine (C) by 3 hydrogen bonds. Thus, statement (d) is false.
Ques. Change in the base sequence of a gene is known as:
- Mutation
- Fission
- Cloning
- Breeding
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Ans. Mutation
Explanation: Mutation is the phenomenon of change in the DNA sequence. It is caused by is either internal factors or external factors such as including smoking, UV rays, environmental conditions, and more. In contrast, cloning is the technique used to create exact copies or clones of a particular gene or DNA.
Ques. Which of the following sets represent pyrimidines present in RNA:
- Uracil and Cytosine
- Adenine and Uracil
- Guanin and Uracil
- Thymine and Uracil
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Ans. Uracil and Cytosine
Explanation: Pyrimidines are a class of heterocyclic nitrogenous bases found in DNA and RNA. While RNA contains the pyrimidines Uracil (U) and Cytosine (C), DNA contains Cytosine (C) and Thiamine (T).
Ques. The crossing of F1 to any of the parents is known as:
- F1 cross
- Test cross
- Back cross
- All of the above
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Ans. Back cross
Explanation: Test cross is a cross between the F1 individual and the recessive parent, while back cross is a cross between the F1 and any of the parents. The test cross helps determine the genotype (homozygous or heterozygous) of the F1 individual, while a back cross can be used to improve the variety or breed by making a number of backcrosses. The F1 cross is a cross between two different parents to produce the F1 hybrid (first filial generation).
Ques. Which of the following statements is true regarding the “law of segregation”?
- The Law of segregation is the law of purity of genes
- Alleles separate from each other during gametogenesis
- Segregation of factors is due to the segregation of chromosomes during meiosis
- All of the above
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Ans. All of the above
Explanation: Mendel’s law of segregation states that alleles do not blend and that both traits are restored as such in the F2 generation, even though one of them is missing in the F1 stage. Further, the alleles of a pair segregate from one another during gametogenesis. This results in the gamete receiving only one of the two components of the alleles.
Ques. An exception to Mendel’s law is:
- Independent assortment
- Linkage
- Purity of gametes
- Dominance
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Ans. Linkage
Explanation: According to the law of independent assortment, inherited genes are independent of each other. However, the linkage is an exception to this law as it influences the isolation of alleles into gametes, i.e., genes that are situated physically close to each other on the same chromosome are more likely to be inherited as a pair. But, due to crossover or recombination, there is a chance for two genes on the same chromosome to behave independently or as linked.
Ques. Mendel used pea plants in his experiments because:
- They were cheap and easily available
- They had contrasting characters
- All of the above
- None of the above
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Ans. They had contrasting characters
Explanation: Mendel used pea plants for his experiments because of the following reasons:
- They have contrasting characters.
- The pea flowers have bisexual characteristics.
- A pure breed of pea plant can be easily obtained through self-fertilization
- Their generation time of pea plant is less.
- They are easy to grow and have excellent disease resistance and optimal rate of survival.
Ques. The smallest unit of genetic material which produces a phenotypic effect on mutation is:
- Muton
- Recon
- Gene
- Cistron
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Ans. Muton
Explanation: Muton is the smallest element, which when altered leads to a mutation, while recon is the smallest part of a chromosome that is capable of undergoing recombination, and cistron is a strand/ segment of the DNA.
Ques. Who rediscovered Mendel’s findings?
- De Vries
- Correns
- Tschermark
- All of the above
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Ans. All of the above
Explanation: Hugo DeVries, Carl Correns and Erich von Tschermak were the botanists who independently rediscovered Mendel's work.
Ques. When the activity of one gene is suppressed by the activity of a non-allelic gene, it is known as:
- Pseudo dominance
- Hypostasis
- Epistasis
- Incomplete dominance
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Ans. Epistasis
Explanation: Epistasis is the process wherein the presence or absence of one gene affects the gene mutation, or one gene masks the effect of another gene. Pseudo dominance is the phenomenon wherein the inheritance of a recessive trait mimics a dominant pattern. In contrast, incomplete dominance is the gene interaction wherein, neither of the two alleles is completely dominant over the other.
Ques. Cystic fibrosis is:
- Sex-linked dominant disorder
- Chromosomal disorder
- Autosomal recessive disorder
- Autosomal dominant disorder
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Ans. Autosomal recessive disorder
Explanation: Cystic fibrosis is an autosomal recessive disorder that is caused by a defect in the 7th chromosome. It is a fatal disease that damages the tissues of the lung and digestive system. The cystic fibrosis transmembrane regulator gene or CFTR gene. is responsible for the occurrence of cystic fibrosis disease.
Since it is a recessive disease, the offspring will be affected only if both the parents will suffer from cystic fibrosis.
Ques. 9:7 ratio of the F2 generation represents which of the following?
- Codominance
- Epistasis
- Complementary interaction
- Incomplete dominance
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Ans. Epistasis
Explanation: The phenotype ratio 9:7 in the F2 generation represents epistasis, a condition wherein the presence or absence of one gene affects the gene mutation, or one gene masks the effect of another gene.
Ques. Which term represents a pair of contrasting characters?
- Allelomorphs
- Codominant genes
- Homozygous
- Heterozygous
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Ans. Allelomorphs
Explanation: Allelomorphs or Alleles are a pair of alternative forms of a gene, i.e., each gene is present in two alternative forms, and each of these forms is called an allele. Each allele controls a single trait that could be either dominant or recessive. For instance, the height of a plant is determined by tallness and dwarfness, wherein tallness is a dominant trait, controlled by a dominant allele “T”, while dwarfness in a plant is a recessive trait, controlled by a recessive allele “t”.
Ques. The geometrical device that helps to find out all the possible combinations of male and female gametes is known as:
- Mendel square
- Punnett square
- Bateson square
- None of the above
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Ans. Punnett square
Explanation: The Punnett square graphically represents all probable genotypes of an entity that can arise from a specific breeding or cross event. It is often used to assess and understand the gamete production and zygote formation of the species being bred or crossed.
Ques. How many phenotypes can occur in the human blood group ABO with alleles IA IB i?
- 1
- 3
- 4
- 2
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Ans. 4
Explanation: For the given alleles, following six different possible genotypes are possible:
IAIB, IAi, IBi, IAIA, IBIB, ii, and the following 4 phenotypes are possible:
- Blood group A (IAIA, IAi)
- Blood group B (IBIB, IBi)
- Blood group AB (IAIB)
- Blood group O (ii).
Ques. A small amount of lethal mutation is always present in the population due to which of the following?
- Positive selection
- Negative selection
- Mutation-selection balance
- Frequency-dependent selection
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Ans. Mutation-selection balance
Explanation: Suppose there is selection against a harmful allele. Eventually, it will be lost from the population. However, new harmful alleles continue to arise over time by mutation. This leads to a certain amount of lethality in the population and also helps establish an equilibrium or balance between mutation and selection.
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