NCERT NEET Biology English Medium Part-1 | Chapter 23 : Principles of Inheritance and variation.

NCERT NEET Biology English Medium Part-1 | Chapter 23 : Principles of Inheritance and variation.

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Question 1: Which of the following traits studied by Mendel in garden peas was a recessive feature?

1. a) Green pod colour.
2. b) Axial flower position.
3. c) Green seed colour.
4. d) Inflated pod shape.

Answer: c) Green seed colour.

Question 2: How many true-breeding pea plant varieties did Mendel select as pairs, which were similar except in one character with contrasting traits?

7. a) 7.
8. b) 14.
9. c) 21.
10. d) 4.

Answer: b) 14.

Question 3: Based on Mendel’s observations, which law states that in a dissimilar pair of factors one member of the pair dominates the other?

1. a) Law of Segregation.
2. b) Law of Independent Assortment.
3. c) Law of Dominance.
4. d) Chromosomal Theory of Inheritance.

Answer: c) Law of Dominance.

Question 4: The proportion of plants with a dwarf phenotype in the F2 generation of a Mendelian monohybrid cross is exactly:

2. a) 1/2.
3. b) 1/3.
4. c) 1/4.
5. d) 3/4.

Answer: c) 1/4.

Question 5: A test cross is performed to determine the genotype of a plant at F2. It involves crossing the F2 plant with:

1. a) A homozygous dominant parent.
2. b) A heterozygous parent.
3. c) A homozygous recessive parent.
4. d) Any plant of the F1 generation.

Answer: c) A homozygous recessive parent.

Question 6: Incomplete dominance is clearly observed in the inheritance of flower colour in:

1. a) Pisum sativum.
2. b) Antirrhinum majus.
3. c) Lathyrus odoratus.
4. d) Oenothera lamarckiana.

Answer: b) Antirrhinum majus.

Question 7: In a cross between true-breeding red-flowered and true-breeding white-flowered snapdragon plants, the F1 generation produces pink flowers. The phenotypic ratio of the F2 generation will be:

1. a) 3:1.
2. b) 1:2:1.
3. c) 9:3:3:1.
4. d) 2:1.

Answer: b) 1:2:1.

Question 8: Which of the following is a classic example of codominance in humans?

1. a) Skin colour.
2. b) Phenylketonuria.
3. c) ABO blood grouping.
4. d) Sickle-cell anaemia trait.

Answer: c) ABO blood grouping.

Question 9: The ABO blood groups are controlled by the gene I. How many alleles of this gene exist in the human population?

1. a) Two.
2. b) Three.
3. c) Four.
4. d) Six.

Answer: b) Three.

Question 10: If a child has blood group O and the father has blood group A, what could be the possible genotype of the mother?

1. a) IAIA.
2. b) IBIB.
3. c) IAIB.
4. d) IBi.

Answer: d) IBi.

Question 11: When more than two alleles govern the same character, it is known as:

1. a) Pleiotropy.
2. b) Polygenic inheritance.
3. c) Multiple allelism.
4. d) Codominance.

Answer: c) Multiple allelism.

Question 12: In the case of starch synthesis in pea seeds, heterozygotes (Bb) produce round seeds with intermediate starch grain size. This is an example of:

1. a) Complete dominance.
2. b) Incomplete dominance.
3. c) Codominance.
4. d) Epistasis.

Answer: b) Incomplete dominance.

Question 13: Mendel’s Law of Independent Assortment is based on the results of:

1. a) Monohybrid crosses.
2. b) Dihybrid crosses.
3. c) Test crosses.
4. d) Back crosses.

Answer: b) Dihybrid crosses.

Question 14: What is the phenotypic ratio obtained in a standard Mendelian dihybrid cross?

1. a) 1:2:1.
2. b) 9:3:3:1.
3. c) 3:1.
4. d) 1:1:1:1.

Answer: b) 9:3:3:1.

Question 15: The chromosomal theory of inheritance, which united Mendelian laws with chromosomal movement, was proposed by:

1. a) T.H. Morgan.
2. b) Gregor Mendel.
3. c) Walter Sutton and Theodore Boveri.
4. d) Alfred Sturtevant.

Answer: c) Walter Sutton and Theodore Boveri.

Question 16: During which phase of meiosis do homologous chromosomes segregate independently of each other?

1. a) Metaphase I.
2. b) Anaphase I.
3. c) Metaphase II.
4. d) Anaphase II.

Answer: b) Anaphase I.

Question 17: Experimental verification of the chromosomal theory of inheritance was provided by:

1. a) Gregor Mendel.
2. b) Sutton and Boveri.
3. c) Thomas Hunt Morgan.
4. d) Hugo de Vries.

Answer: c) Thomas Hunt Morgan.

Question 18: Why did Morgan choose Drosophila melanogaster for his genetic experiments?

1. a) They have a very long life cycle.
2. b) They produce very few offspring per mating.
3. c) They can be grown on simple synthetic medium.
4. d) Male and female flies are morphologically identical.

Answer: c) They can be grown on simple synthetic medium.

Question 19: The physical association or functional connection between two genes on a chromosome is termed:

1. a) Segregation.
2. b) Linkage.
3. c) Assortment.
4. d) Mutation.

Answer: b) Linkage.

Question 20: T.H. Morgan observed that when two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations was:

1. a) Equal to the non-parental type.
2. b) Much lower than the non-parental type.
3. c) Much higher than the non-parental type.
4. d) Always zero.

Answer: c) Much higher than the non-parental type.

Question 21: Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes to:

1. a) Determine the sex of the organism.
2. b) Map their position on the chromosome.
3. c) Induce mutations.
4. d) Prove the law of dominance.

Answer: b) Map their position on the chromosome.

Question 22: Human skin colour is controlled by three different genes. This type of inheritance is called:

1. a) Pleiotropy.
2. b) Multiple allelism.
3. c) Polygenic inheritance.
4. d) Codominance.

Answer: c) Polygenic inheritance.

Question 23: In polygenic inheritance, the phenotype reflects the contribution of each allele. This effect is described as:

1. a) Recessive.
2. b) Dominant.
3. c) Additive.
4. d) Epistatic.

Answer: c) Additive.

Question 24: A single gene that exhibits multiple phenotypic expressions is called a:

1. a) Polygenic gene.
2. b) Pleiotropic gene.
3. c) Multiple allele.
4. d) Pseudoallele.

Answer: b) Pleiotropic gene.

Question 25: Phenylketonuria is an example of pleiotropy in humans. It is caused by a mutation in the gene that codes for:

1. a) Tyrosine hydroxylase.
2. b) Phenylalanine hydroxylase.
3. c) Homogentisic acid oxidase.
4. d) Tyrosinase.

Answer: b) Phenylalanine hydroxylase.

Question 26: The 'X body' discovered by Henking in spermatogenesis of some insects was later identified as:

1. a) Y chromosome.
2. b) X chromosome.
3. c) Autosome.
4. d) Nucleolus.

Answer: b) X chromosome.

Question 27: Which of the following organisms exhibits the XO type of sex determination?

1. a) Human beings.
2. b) Drosophila.
3. c) Grasshopper.
4. d) Birds.

Answer: c) Grasshopper.

Question 28: In the XY type of sex determination seen in humans and Drosophila, the males have:

1. a) Two X chromosomes.
2. b) Two Y chromosomes.
3. c) One X and one Y chromosome.
4. d) Only one X chromosome and no Y.

Answer: c) One X and one Y chromosome.

Question 29: In which of the following is female heterogamety observed?

1. a) Humans.
2. b) Drosophila.
3. c) Grasshoppers.
4. d) Birds.

Answer: d) Birds.

Question 30: The sex of the chicks in birds is determined by the formula:

1. a) XX-XY.
2. b) XX-XO.
3. c) ZZ-ZW.
4. d) ZZ-ZO.

Answer: c) ZZ-ZW.

Question 31: A phenomenon which results in the alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism is:

1. a) Recombination.
2. b) Linkage.
3. c) Mutation.
4. d) Crossing over.

Answer: c) Mutation.

Question 32: Sickle-cell anaemia is an example of which type of mutation?

1. a) Deletion mutation.
2. b) Frameshift mutation.
3. c) Point mutation.
4. d) Chromosomal nondisjunction.

Answer: c) Point mutation.

Question 33: Chemical and physical factors that induce mutations are referred to as:

1. a) Carcinogens.
2. b) Teratogens.
3. c) Mutagens.
4. d) Pathogens.

Answer: c) Mutagens.

Question 34: The analysis of traits in a several of generations of a family is called:

1. a) Karyotyping.
2. b) Pedigree analysis.
3. c) DNA fingerprinting.
4. d) Genetic drift.

Answer: b) Pedigree analysis.

Question 35: In a pedigree chart, a square symbol typically represents:

1. a) An affected female.
2. b) A normal male.
3. c) A normal female.
4. d) Mating.

Answer: b) A normal male.

Question 36: Mendelian disorders are mainly determined by:

1. a) Alteration in the number of chromosomes.
2. b) Alteration or mutation in a single gene.
3. c) Deletion of a part of a chromosome.
4. d) Duplication of an entire chromosome set.

Answer: b) Alteration or mutation in a single gene.

Question 37: Which of the following is an autosomal dominant Mendelian disorder?

1. a) Haemophilia.
2. b) Sickle-cell anaemia.
3. c) Myotonic dystrophy.
4. d) Phenylketonuria.

Answer: c) Myotonic dystrophy.

Question 38: Colour blindness is an X-linked recessive trait. A carrier woman marries a normal man. What is the probability that their son will be colour blind?

1. a) 0 percent.
2. b) 25 percent.
3. c) 50 percent.
4. d) 100 percent.

Answer: c) 50 percent.

Question 39: Haemophilia is an X-linked recessive disease. It shows its transmission from:

1. a) Carrier female to male progeny.
2. b) Carrier female to female progeny only.
3. c) Affected male to male progeny.
4. d) Affected male to all his progeny.

Answer: a) Carrier female to male progeny.

Question 40: Why is the possibility of a female becoming haemophilic extremely rare?

1. a) Her father must be a carrier and mother haemophilic.
2. b) Her mother has to be at least a carrier and father should be haemophilic.
3. c) The gene is located on the Y chromosome.
4. d) Haemophilia is a dominant trait in females.

Answer: b) Her mother has to be at least a carrier and father should be haemophilic.

Question 41: Sickle-cell anaemia is controlled by a single pair of alleles, HbA and HbS. The disease phenotype is exhibited only by the genotype:

1. a) HbA HbA.
2. b) HbA HbS.
3. c) HbS HbS.
4. d) Both HbA HbS and HbS HbS.

Answer: c) HbS HbS.

Question 42: The mutation causing sickle-cell anaemia is the substitution of glutamic acid by:

1. a) Valine.
2. b) Tyrosine.
3. c) Phenylalanine.
4. d) Tryptophan.

Answer: a) Valine.

Question 43: In sickle cell anaemia, the amino acid substitution occurs at which position of the beta globin chain of the haemoglobin molecule?

1. a) Fifth.
2. b) Sixth.
3. c) Seventh.
4. d) Eighth.

Answer: b) Sixth.

Question 44: Phenylketonuria is an inherited disease characterized by:

1. a) Autosomal dominant trait.
2. b) X-linked recessive trait.
3. c) Autosomal recessive trait.
4. d) Y-linked trait.

Answer: c) Autosomal recessive trait.

Question 45: The accumulation of phenylalanine and its derivatives in the brain of a phenylketonuria patient results in:

1. a) Kidney failure.
2. b) Mental retardation.
3. c) Blindness.
4. d) Heart enlargement.

Answer: b) Mental retardation.

Question 46: Thalassemia is an autosomal recessive blood disease. Unlike sickle-cell anaemia which is a qualitative problem, Thalassemia is:

1. a) Also a qualitative problem.
2. b) A quantitative problem of synthesising too few globin molecules.
3. c) Caused by a point mutation in the start codon.
4. d) Caused by infection.

Answer: b) A quantitative problem of synthesising too few globin molecules.

Question 47: Alpha Thalassemia is controlled by two closely linked genes HBA1 and HBA2 located on which chromosome?

11. a) Chromosome 11.
12. b) Chromosome 16.
13. c) Chromosome 21.
14. d) X Chromosome.

Answer: b) Chromosome 16.

Question 48: Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome, called:

1. a) Polyploidy.
2. b) Aneuploidy.
3. c) Translocation.
4. d) Inversion.

Answer: b) Aneuploidy.

Question 49: Down’s syndrome is caused by the presence of an additional copy of:

13. a) Chromosome 13.
14. b) Chromosome 18.
15. c) Chromosome 21.
16. d) X Chromosome.

Answer: c) Chromosome 21.

Question 50: The genetic constitution of an individual with Klinefelter’s syndrome is:

1. a) 44 Autosomes + XO.
2. b) 44 Autosomes + XXY.
3. c) 44 Autosomes + XYY.
4. d) 44 Autosomes + XXX.

Answer: b) 44 Autosomes + XXY.

Question 51: Which of the following features is classically associated with Turner’s syndrome?

1. a) Tall stature and aggressive behaviour.
2. b) Presence of gynaecomastia.
3. c) Rudimentary ovaries and sterility.
4. d) Broad palm with characteristic palm crease.

Answer: c) Rudimentary ovaries and sterility.

Question 52: Gynaecomastia, the development of breast tissue in males, is a prominent feature of:

1. a) Down's syndrome.
2. b) Turner's syndrome.
3. c) Klinefelter's syndrome.
4. d) Phenylketonuria.

Answer: c) Klinefelter's syndrome.

Question 53: A broad flat face, partially open mouth with a furrowed tongue, and congenital heart disease are physical symptoms of:

1. a) Sickle-cell anaemia.
2. b) Turner's syndrome.
3. c) Klinefelter's syndrome.
4. d) Down's syndrome.

Answer: d) Down's syndrome.

Question 54: Who first described the chromosomal disorder that leads to Down's syndrome in 1866?

1. a) Langdon Down.
2. b) T.H. Morgan.
3. c) Gregor Mendel.
4. d) Walter Sutton.

Answer: a) Langdon Down.

Question 55: The chromosomal disorder caused due to the absence of one of the X chromosomes in females is:

1. a) Down's syndrome.
2. b) Klinefelter's syndrome.
3. c) Turner's syndrome.
4. d) Edward's syndrome.

Answer: c) Turner's syndrome.

Question 56: A classic example of a cross where the F1 phenotype does not resemble either of the two parents and is in between the two is:

1. a) Inheritance of seed shape in peas.
2. b) Inheritance of flower colour in dog flower.
3. c) Inheritance of blood groups in humans.
4. d) Inheritance of pod colour in peas.

Answer: b) Inheritance of flower colour in dog flower.

Question 57: If a woman with blood type AB marries a man with blood type O, what are the possible blood types of their offspring?

1. a) A and B only.
2. b) AB and O only.
3. c) A, B, AB, and O.
4. d) O only.

Answer: a) A and B only.

Question 58: Mendel crossed a tall pea plant with a dwarf pea plant. If the tall parent was heterozygous, what phenotypic ratio would be expected in the offspring?

1. a) 3 Tall : 1 Dwarf.
2. b) All Tall.
3. c) 1 Tall : 1 Dwarf.
4. d) All Dwarf.

Answer: c) 1 Tall : 1 Dwarf.

Question 59: The term 'Linkage' was coined by:

1. a) Gregor Mendel.
2. b) Carl Correns.
3. c) Thomas Hunt Morgan.
4. d) William Bateson.

Answer: c) Thomas Hunt Morgan.

Question 60: Polyploidy is typically a result of:

1. a) Failure of cytokinesis after telophase stage of cell division.
2. b) Failure of sister chromatids to separate during anaphase.
3. c) Deletion of a segment of a chromosome.
4. d) Point mutation in a critical regulatory gene.

Answer: a) Failure of cytokinesis after telophase stage of cell division.

Question 61: Beta Thalassemia is controlled by a single gene HBB located on which chromosome?

11. a) Chromosome 11.
12. b) Chromosome 16.
13. c) Chromosome 21.
14. d) X Chromosome.

Answer: a) Chromosome 11.

Question 62: Which of the following crosses will yield a phenotypic ratio of 1:1:1:1?

1. a) AaBb x AaBb.
2. b) AaBb x aabb.
3. c) AABB x aabb.
4. d) Aabb x aaBB.

Answer: b) AaBb x aabb.

Question 63: The mechanism of sex determination in honeybees is based on the number of sets of chromosomes an individual receives. This is known as:

1. a) Haplo-diploid sex determination.
2. b) XX-XY sex determination.
3. c) ZZ-ZW sex determination.
4. d) Environmental sex determination.

Answer: a) Haplo-diploid sex determination.

Question 64: In the haplo-diploid sex determination system of honeybees, males (drones) are formed by:

1. a) Fertilization of an egg by a sperm.
2. b) Parthenogenesis from unfertilized eggs.
3. c) Meiosis in diploid females.
4. d) Mitosis in haploid females.

Answer: b) Parthenogenesis from unfertilized eggs.

Question 65: Which of the following statements about male honeybees is correct?

1. a) They have 32 chromosomes.
2. b) They produce sperms by meiosis.
3. c) They do not have a father and cannot have sons.
4. d) They are diploid organisms.

Answer: c) They do not have a father and cannot have sons.

Question 66: Which scientists independently rediscovered Mendel’s results on the inheritance of characters in 1900?

1. a) Morgan, Sturtevant, and Bridges.
2. b) de Vries, Correns, and von Tschermak.
3. c) Sutton, Boveri, and Avery.
4. d) Watson, Crick, and Wilkins.

Answer: b) de Vries, Correns, and von Tschermak.

Question 67: In a pedigree, a solid circle represents:

1. a) An affected male.
2. b) A normal female.
3. c) An affected female.
4. d) Carrier male.

Answer: c) An affected female.

Question 68: If two genes are tightly linked on the same chromosome, they show:

1. a) Very high recombination.
2. b) 50% recombination.
3. c) Very low recombination.
4. d) Independent assortment.

Answer: c) Very low recombination.

Question 69: In Morgan's dihybrid cross for eye colour and wing size in Drosophila, the recombination frequency between the genes was found to be:

1. a) 1.3%.
2. b) 37.2%.
3. c) 50.0%.
4. d) 98.7%.

Answer: b) 37.2%.

Question 70: A male human is heterozygous for autosomal genes A and B and is also hemizygous for hemophilic gene h. What proportion of his sperms will carry the a, b, and h genes?

2. a) 1/2.
3. b) 1/4.
4. c) 1/8.
5. d) 1/16.

Answer: c) 1/8.

Question 71: The gene causing sickle-cell anaemia is lethal in the homozygous condition. The survival of the allele in populations, particularly in Africa, is due to:

1. a) Its high mutation rate.
2. b) Heterozygote advantage against malaria.
3. c) Genetic drift.
4. d) Polyploidy.

Answer: b) Heterozygote advantage against malaria.

Question 72: A cross between a tall pea plant (TT) and a dwarf pea plant (tt) yields all tall plants in the F1. This shows that the tall trait is:

1. a) Recessive.
2. b) Dominant.
3. c) Codominant.
4. d) Incompletely dominant.

Answer: b) Dominant.

Question 73: The graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross is called a:

1. a) Pedigree chart.
2. b) Karyotype.
3. c) Punnett square.
4. d) Linkage map.

Answer: c) Punnett square.

Question 74: Punnett square was developed by a:

1. a) German botanist.
2. b) British geneticist.
3. c) Austrian monk.
4. d) American geneticist.

Answer: b) British geneticist.

Question 75: In a Mendelian dihybrid cross, the probability of obtaining an offspring with the genotype AABB is:

16. a) 1/16.
17. b) 3/16.
18. c) 9/16.
19. d) 1/4.

Answer: a) 1/16.

Question 76: The allele for normal vision is dominant to the allele for color blindness. If a normal man marries a carrier woman, the chance of their daughters being color blind is:

1. a) 0%.
2. b) 25%.
3. c) 50%.
4. d) 100%.

Answer: a) 0%.

Question 77: Which genetic disorder is characterized by a karyotype of 45, X?

1. a) Down's syndrome.
2. b) Klinefelter's syndrome.
3. c) Turner's syndrome.
4. d) Edward's syndrome.

Answer: c) Turner's syndrome.

Question 78: Mutations that involve the deletion or insertion of base pairs of DNA, shifting the reading frame, are known as:

1. a) Nonsense mutations.
2. b) Silent mutations.
3. c) Frameshift mutations.
4. d) Missense mutations.

Answer: c) Frameshift mutations.

Question 79: The phenomenon where a single gene product may produce more than one effect is best illustrated by:

1. a) The ABO blood group system.
2. b) Starch grain size in pea seeds.
3. c) Human skin color.
4. d) Eye color in Drosophila.

Answer: b) Starch grain size in pea seeds.

Question 80: What was the main reason for Mendel's success in his breeding experiments?

1. a) He studied multiple traits simultaneously from the beginning.
2. b) He chose to work on complex quantitative traits.
3. c) He used statistical methods and mathematical logic for analyzing data.
4. d) He observed linkage in all his crosses.

Answer: c) He used statistical methods and mathematical logic for analyzing data.

Question 81: An organism with two identical alleles for a given trait is said to be:

1. a) Heterozygous.
2. b) Hemizygous.
3. c) Homozygous.
4. d) Heterogametic.

Answer: c) Homozygous.

Question 82: What is the genotype of a plant that is true-breeding for a dominant trait?

1. a) Heterozygous.
2. b) Homozygous dominant.
3. c) Homozygous recessive.
4. d) Hemizygous dominant.

Answer: b) Homozygous dominant.

Question 83: If the sequence of genes on a chromosome is A-B-C-D, and the recombination frequency between A and B is 5%, A and C is 15%, B and C is 10%, the order of genes confirms that the map distance between A and C is:

1. a) 5 centiMorgans.
2. b) 10 centiMorgans.
3. c) 15 centiMorgans.
4. d) 20 centiMorgans.

Answer: c) 15 centiMorgans.

Question 84: Pedigree analysis is utilized because in human genetics:

1. a) Controlled crosses cannot be performed.
2. b) Humans have too few chromosomes.
3. c) The generation time is very short.
4. d) Human traits do not follow Mendelian laws.

Answer: a) Controlled crosses cannot be performed.

Question 85: The mutant haemoglobin molecule in sickle-cell anaemia undergoes polymerization under low oxygen tension causing the change in shape of RBCs from biconcave disc to:

1. a) Spherical structure.
2. b) Elongated sickle-like structure.
3. c) Star-shaped structure.
4. d) Spindle-shaped structure.

Answer: b) Elongated sickle-like structure.

Question 86: Which of the following is a symptom of Phenylketonuria?

1. a) Enlargement of the liver.
2. b) Decrease in pigmentation of hair and skin.
3. c) Iron overload.
4. d) Premature aging.

Answer: b) Decrease in pigmentation of hair and skin.

Question 87: What dictates the pairing and segregation of homologous chromosomes during meiosis?

1. a) The spindle apparatus.
2. b) The centromere alone.
3. c) The telomeres.
4. d) Their homology and the synaptonemal complex.

Answer: a) The spindle apparatus.

Question 88: The frequency of crossing over between any two linked genes is:

1. a) Directly proportional to the distance between them.
2. b) Inversely proportional to the distance between them.
3. c) Always 50 percent.
4. d) Independent of the distance between them.

Answer: a) Directly proportional to the distance between them.

Question 89: Which type of sex determination occurs in organisms where females produce two different types of gametes?

1. a) Male heterogamety.
2. b) Female heterogamety.
3. c) Haplo-diploidy.
4. d) Environmental determination.

Answer: b) Female heterogamety.

Question 90: An individual affected with Down's syndrome has a total of how many chromosomes?

45. a) 45.
46. b) 46.
47. c) 47.
48. d) 48.

Answer: c) 47.

Question 91: The concept of multiple alleles is applicable when:

1. a) A gene is present on multiple chromosomes.
2. b) An individual possesses more than two alleles for a trait.
3. c) A population possesses more than two alleles for a specific trait.
4. d) A trait is controlled by many genes.

Answer: c) A population possesses more than two alleles for a specific trait.

Question 92: Which of the following is true for the inheritance of Haemophilia?

1. a) It primarily affects females.
2. b) The gene is located on the autosomes.
3. c) An affected father will pass the disease to all his sons.
4. d) A carrier mother has a 50% chance of passing the defective gene to her sons.

Answer: d) A carrier mother has a 50% chance of passing the defective gene to her sons.

Question 93: What term did Mendel use for the inherited entities that determine traits, which we now call genes?

1. a) Chromosomes.
2. b) Alleles.
3. c) Factors.
4. d) Chromatids.

Answer: c) Factors.

Question 94: In a cross AaBb x AaBb, what fraction of the offspring will be homozygous for both recessive traits (aabb)?

16. a) 1/16.
17. b) 3/16.
18. c) 9/16.
19. d) 1/4.

Answer: a) 1/16.

Question 95: If an organism's genotype for two linked genes is AB/ab, which of the following gametes represents a recombinant type?

1. a) AB.
2. b) ab.
3. c) Ab.
4. d) Both AB and ab.

Answer: c) Ab.

Question 96: What genetic disorder is characterized by a failure of the body to produce the enzyme required for the conversion of phenylalanine to tyrosine?

1. a) Alkaptonuria.
2. b) Phenylketonuria.
3. c) Tyrosinemia.
4. d) Albinism.

Answer: b) Phenylketonuria.

Question 97: Which observation in the F2 generation of his monohybrid crosses led Mendel to propose the Law of Segregation?

1. a) Blending of traits.
2. b) Appearance of the recessive trait without blending.
3. c) Uniformity of the dominant trait.
4. d) The continuous variation of phenotypes.

Answer: b) Appearance of the recessive trait without blending.

Question 98: A mutation that results in the replacement of a purine base with a pyrimidine base is technically a form of:

1. a) Transition.
2. b) Transversion.
3. c) Frameshift.
4. d) Deletion.

Answer: b) Transversion.

Question 99: When a single gene affects several seemingly unrelated aspects of a phenotype, the phenomenon is called:

1. a) Polygeny.
2. b) Epistasis.
3. c) Pleiotropy.
4. d) Codominance.

Answer: c) Pleiotropy.

Question 100: Which of the following conditions represents an example of aneuploidy in humans resulting from non-disjunction of autosomes?

1. a) Turner's syndrome.
2. b) Klinefelter's syndrome.
3. c) Down's syndrome.
4. d) Sickle-cell anaemia.

Answer: c) Down's syndrome.

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