The Most Comprehensive Question Bank for ICSE Class 10 Students
Multiple Choice Questions (MCQs)
1) What is the genotype of a female who is a carrier for color blindness?
a) X^C X^c
b) X^c Y
c) X^C Y
d) X^c X^c
Solution: a) X^C X^c
Explanation: A female carrier for X-linked diseases like color blindness has one normal allele and one disease allele. Since color blindness is X-linked, she has the genotype X^C X^c, where X^C is normal and X^c is the color blindness allele.
2) Which of the following is a characteristic of homozygous genotypes?
a) Two different alleles for a trait
b) Two identical alleles for a trait
c) One dominant and one recessive allele
d) No alleles for a given trait
Solution: b) Two identical alleles for a trait
Explanation: Homozygous genotypes consist of two identical alleles, either both dominant or both recessive, for a specific trait.
3) In Mendel’s pea plants, what is the expected phenotypic ratio of a cross between two heterozygous tall plants (Tt)?
a) 3 tall : 1 short
b) All tall
c) 1 tall : 1 short
d) All short
Solution: a) 3 tall : 1 short
Explanation: In a cross between two heterozygous tall pea plants (Tt x Tt), the expected phenotypic ratio is 3 tall : 1 short due to Mendelian inheritance patterns.
4) Which term best describes a pair of genes where one is dominant and the other is recessive?
a) Homozygous
b) Heterozygous
c) Hemizygous
d) Homologous
Solution: b) Heterozygous
Explanation: Heterozygous refers to having two different alleles for a particular gene, one dominant and one recessive.
5) What is the probability of having a son who is color blind when a normal vision father and a carrier mother have a child?
a) 25%
b) 50%
c) 0%
d) 75%
Solution: b) 50%
Explanation: The mother (carrier) has a 50% chance of passing the color blind allele (X^c) to her son. Since males have only one X chromosome, receiving the X^c allele will result in color blindness.
6) Which of Mendel’s laws explains the inheritance of two or more traits independently?
a) Law of Dominance
b) Law of Segregation
c) Law of Independent Assortment
d) Law of Uniformity
Solution: c) Law of Independent Assortment
Explanation: The Law of Independent Assortment states that alleles for separate traits are passed independently of one another from parents to offspring.
7) In a monohybrid cross of two heterozygous organisms, what is the expected genotypic ratio in the offspring?
a) 1:2:1
b) 3:1
c) 1:1
d) 2:1
Solution: a) 1:2:1
Explanation: In a monohybrid cross involving heterozygous organisms (e.g., Aa x Aa), the genotypic ratio is typically 1 AA : 2 Aa : 1 aa.
8) What is the expected phenotype of an individual with a genotype of X^c Y for color blindness?
a) Color blind
b) Not color blind
c) Carrier of color blindness
d) Unable to determine
Solution: a) Color blind
Explanation: An individual with the genotype X^c Y is a male (Y chromosome present) with only one X chromosome carrying the allele for color blindness (X^c), thus he will be color blind.
9) Which of the following is true for a dihybrid cross of heterozygous parents (AaBb x AaBb)?
a) 9:3:3:1 phenotypic ratio
b) 3:1 phenotypic ratio
c) 1:2:1 genotypic ratio
d) 1:1 phenotypic ratio
Solution: a) 9:3:3:1 phenotypic ratio
Explanation: A dihybrid cross of heterozygous parents (AaBb x AaBb) typically results in a 9:3:3:1 phenotypic ratio according to Mendelian genetics.
10) What is the phenotype of an individual with a heterozygous genotype for a dominant trait?
a) Will show the recessive trait
b) Will show a blend of traits
c) Will show the dominant trait
d) Cannot be determined
Solution: c) Will show the dominant trait
Explanation: In cases of simple dominance, an individual with a heterozygous genotype (e.g., Aa) will exhibit the phenotype of the dominant trait.
11) In humans, the gene for normal blood clotting is dominant over the gene for hemophilia. What is the genotype of a female carrier for hemophilia?
a) HH
b) Hh
c) hh
d) Cannot be determined
Solution: b) Hh
Explanation: A female carrier for hemophilia possesses one normal allele (H) and one hemophilia allele (h), making her genotype Hh.
12) If a pea plant with yellow seeds (YY) is crossed with a plant with green seeds (yy), what will be the seed color in the F1 generation?
a) All yellow
b) All green
c) 50% yellow, 50% green
d) 75% yellow, 25% green
Solution: a) All yellow
Explanation: Yellow seed color (Y) is dominant over green (y). Crossing YY (yellow) with yy (green) will result in all offspring being Yy (yellow) in the F1 generation.
13) Which of the following is an example of a sex-linked trait in humans?
a) Blood type
b) Eye color
c) Hemophilia
d) Height
Solution: c) Hemophilia
Explanation: Hemophilia is an example of a sex-linked trait, specifically linked to the X chromosome in humans.
14) In a Mendelian monohybrid cross, what is the expected ratio of dominant to recessive phenotypes in the F2 generation?
a) 3:1
b) 1:2:1
c) 1:1
d) All dominant
Solution: a) 3:1
Explanation: In a Mendelian monohybrid cross, the F2 generation typically shows a 3:1 ratio of dominant to recessive phenotypes.
15) What does the term ‘genotype’ refer to?
a) The physical appearance of an organism
b) The genetic makeup of an organism
c) The environment in which an organism lives
d) The way an organism reacts to its environment
Solution: b) The genetic makeup of an organism
Explanation: The genotype refers to the genetic constitution of an organism, i.e., the specific allele combination an organism carries.
16) In pea plants, the allele for tall (T) is dominant over the allele for dwarf (t). What is the expected phenotype of a plant with the Tt genotype?
a) Tall
b) Dwarf
c) Intermediate height
d) Variegated height
Solution: a) Tall
Explanation: Since T (tall) is dominant over t (dwarf), a plant with a Tt genotype will exhibit the tall phenotype.
17) Which term describes an organism with two identical alleles for a trait?
a) Heterozygous
b) Homozygous
c) Hybrid
d) Hemizygous
Solution: b) Homozygous
Explanation: Homozygous refers to having two identical alleles for a particular trait, either both dominant or both recessive.
18) In a cross between a homozygous dominant tall pea plant (TT) and a homozygous recessive dwarf plant (tt), what will be the height of the F1 generation?
a) All tall
b) All dwarf
c) Half tall, half dwarf
d) Mixed heights
Solution: a) All tall
Explanation: Since tall is dominant, all offspring (Tt) of a cross between TT and tt will exhibit the tall phenotype.
19) What is the probability of a child being affected by a recessive genetic disorder if both parents are carriers?
a) 25%
b) 50%
c) 75%
d) 100%
Solution: a) 25%
Explanation: If both parents are carriers (heterozygous for a recessive disorder), there’s a 25% chance for the child to inherit both recessive alleles and be affected.
20) A dihybrid cross results in a 9:3:3:1 ratio. What does this ratio represent?
a) Genotypes of offspring
b) Phenotypes of offspring
c) Dominant and recessive traits
d) Genetic mutations
Solution: b) Phenotypes of offspring
Explanation: The 9:3:3:1 ratio in a dihybrid cross represents the phenotypic distribution of the offspring.
21) In humans, which chromosome pair determines the sex of the offspring?
a) Chromosome 1
b) Chromosome 21
c) Chromosome X and Y
d) Chromosome 2
Solution: c) Chromosome X and Y
Explanation: The sex of the offspring is determined by the combination of sex chromosomes, X and Y.
22) What is the result of a cross between a color-blind male (X^c Y) and a carrier female (X^C X^c)?
a) All children will be color blind
b) All sons will be color blind
c) No children will be color blind
d) Some children may be color blind
Solution: d) Some children may be color blind
Explanation: The sons have a 50% chance of being color blind (receiving X^c), and the daughters have a 50% chance of being carriers.
23) In Mendelian genetics, what does the term ‘dominant’ refer to?
a) An allele that is always expressed
b) An allele that is rarely expressed
c) An allele that mixes with others
d) An allele that suppresses others
Solution: a) An allele that is always expressed
Explanation: A dominant allele is one that is expressed in the phenotype, even when only one copy is present in the genotype.
24) Which is not a Mendelian factor?
a) Gene
b) Allele
c) Mutation
d) Chromosome
Solution: d) Chromosome
Explanation: Mendelian factors refer to genes and alleles, not to structures like chromosomes.
25) What is the expected phenotypic ratio in the offspring of a cross between two heterozygous parents for a trait with complete dominance?
a) 1:2:1
b) 3:1
c) 2:1:1
d) 4:0
Solution: b) 3:1
Explanation: In a cross between two heterozygous parents (Aa x Aa) for a trait with complete dominance, the expected phenotypic ratio is 3 dominant: 1 recessive.
26) Which of the following best describes an allele?
a) A version of a gene
b) A type of chromosome
c) A genetic disorder
d) A kind of protein
Solution: a) A version of a gene
Explanation: An allele is a variant form of a gene.
27) If a plant is homozygous recessive for a trait, what will be the appearance of its offspring when crossed with a heterozygous plant?
a) All showing the dominant trait
b) All showing the recessive trait
c) A mix of dominant and recessive traits
d) Half showing the dominant trait, half showing the recessive
Solution: c) A mix of dominant and recessive traits
Explanation: The offspring will have a mix, with a 1:1 genotypic ratio (half heterozygous dominant, half homozygous recessive) and most showing the dominant trait.
28) In humans, how many chromosomes are present in each cell after fertilization?
a) 23
b) 46
c) 92
d) 2
Solution: b) 46
Explanation: Each human cell contains 46 chromosomes (23 pairs) after fertilization, with one set from each parent.
29) Which process ensures that the alleles for a trait separate during gamete formation?
a) Fertilization
b) Mutation
c) Segregation
d) Replication
Solution: c) Segregation
Explanation: Mendel’s Law of Segregation states that allele pairs separate or segregate during gamete formation.
30) A pea plant with the genotype TtYy will produce how many types of gametes?
a) 2
b) 4
c) 8
d) 16
Solution: b) 4
Explanation: A plant with genotype TtYy can produce four types of gametes: TY, Ty, tY, and ty.
31) What is the expected ratio of offspring phenotypes in a cross between two pea plants, both with the genotype TtYy?
a) 9:3:3:1
b) 3:1
c) 1:2:1
d) 1:1:1:1
Solution: a) 9:3:3:1
Explanation: The cross of TtYy x TtYy in pea plants typically results in a 9:3:3:1 phenotypic ratio in the offspring.
32) In a pedigree chart, what does a shaded circle represent?
a) A male carrier
b) A female carrier
c) An affected female
d) An affected male
Solution: c) An affected female
Explanation: In pedigree charts, a shaded circle usually indicates an affected female.
33) What is the genotypic ratio in the F2 generation of a Mendelian monohybrid cross?
a) 3:1
b) 1:2:1
c) 9:3:3:1
d) 1:1
Solution: b) 1:2:1
Explanation: The genotypic ratio in the F2 generation of a monohybrid cross (such as Aa x Aa) is 1 homozygous dominant (AA) : 2 heterozygous (Aa) : 1 homozygous recessive (aa).
34) Which of the following is an example of a homozygous genotype?
a) Aa
b) aa
c) AB
d) Ab
Solution: b) aa
Explanation: A homozygous genotype consists of two identical alleles for a particular gene, such as aa or AA.
35) In a typical Mendelian dihybrid cross (AaBb x AaBb), what proportion of the offspring will have both dominant traits?
a) 9/16
b) 3/16
c) 1/16
d) 6/16
Solution: a) 9/16
Explanation: In a dihybrid cross (AaBb x AaBb), the proportion of offspring with both dominant traits is 9 out of 16.
36) What is the main purpose of a Punnett square in genetic studies?
a) To identify genetic mutations
b) To predict the outcome of genetic crosses
c) To determine the actual genotype of an organism
d) To map out chromosomes
Solution: b) To predict the outcome of genetic crosses
Explanation: A Punnett square is used to predict the probability of an offspring having a particular genotype based on the genotypes of its parents.
37) In genetics, what is the meaning of the term ‘phenotype’?
a) The genetic makeup of an organism
b) The physical appearance or characteristics of an organism
c) The location of a gene on a chromosome
d) The total number of chromosomes in an organism
Solution: b) The physical appearance or characteristics of an organism
Explanation: Phenotype refers to the observable physical properties of an organism, which are influenced by both genetic and environmental factors.
38) If two parents are carriers for a recessive genetic disorder, what is the probability that their child will be a carrier?
a) 25%
b) 50%
c) 75%
d) 100%
Solution: b) 50%
Explanation: If both parents are carriers (heterozygous, such as Aa), there’s a 50% chance that a child will also be a carrier.
39) What does a test cross in genetics aim to determine?
a) The dominant trait
b) The recessive trait
c) The genotype of an organism with a dominant phenotype
d) The phenotype of an organism with a recessive genotype
Solution: c) The genotype of an organism with a dominant phenotype
Explanation: A test cross is used to determine the genotype of an individual expressing a dominant phenotype by crossing it with an individual expressing the recessive phenotype.
40) What would be the genotypic ratio in the offspring of a cross between a homozygous dominant individual (AA) and a homozygous recessive individual (aa)?
a) 1:0
b) 1:1
c) 1:2:1
d) 0:1
Solution: a) 1:0
Explanation: All offspring from this cross (AA x aa) would have the genotype Aa, making the genotypic ratio 1:0 (all heterozygous).
41) Which genetic principle explains the recombination of genes due to crossing over?
a) Law of Dominance
b) Law of Independent Assortment
c) Law of Segregation
d) Law of Linkage
Solution: d) Law of Linkage
Explanation: The Law of Linkage explains how genes that are close together on the same chromosome tend to be inherited together, but crossing over can lead to recombination of these genes.
42) In a cross involving two heterozygous pea plants (Tt), what is the probability of producing a tall plant?
a) 25%
b) 50%
c) 75%
d) 100%
Solution: c) 75%
Explanation: In a cross between two heterozygous pea plants (Tt x Tt), the probability of producing a tall plant (TT or Tt) is 75%.
43) What is the purpose of a pedigree chart in genetics?
a) To predict future genetic mutations
b) To trace the inheritance of a trait through several generations
c) To show the physical characteristics of an organism
d) To map out the entire genome of an organism
Solution: b) To trace the inheritance of a trait through several generations
Explanation: Pedigree charts are used to track the inheritance of specific traits through multiple generations in a family.
44) If a colorblind man (X^cY) has children with a woman who is not a carrier for colorblindness (X^CX^C), what is the likelihood their sons will be colorblind?
a) 0%
b) 25%
c) 50%
d) 100%
Solution: a) 0%
Explanation: Since the mother provides only X^C alleles and the father provides the Y chromosome to sons, none of the sons will be colorblind.
45) What is the expected phenotypic ratio in the F2 generation of a dihybrid cross (AaBb x AaBb)?
a) 3:1
b) 9:3:3:1
c) 1:1:1:1
d) 1:2:1
Solution: b) 9:3:3:1
Explanation: In a dihybrid cross (AaBb x AaBb), the expected phenotypic ratio in the F2 generation is 9:3:3:1.
46) Which of the following is true for an organism with a heterozygous genotype?
a) It has two different alleles for a trait.
b) It has two identical alleles for a trait.
c) It expresses only the recessive trait.
d) It cannot pass on the dominant allele.
Solution: a) It has two different alleles for a trait.
Explanation: A heterozygous genotype consists of two different alleles for a trait, one dominant and one recessive.
47) In humans, which of the following is a characteristic of autosomal recessive inheritance?
a) Affected individuals have two copies of the mutant gene.
b) Males are more frequently affected than females.
c) It is passed only through the maternal line.
d) It is always visible in the phenotype.
Solution: a) Affected individuals have two copies of the mutant gene.
Explanation: Autosomal recessive inheritance requires individuals to have two copies of the mutant gene to express the trait.
48) In a monohybrid cross, what is the ratio of homozygous dominant to homozygous recessive genotypes in the F2 generation?
a) 1:1
b) 1:2:1
c) 3:1
d) 0:1
Solution: b) 1:2:1
Explanation: The genotypic ratio in the F2 generation of a monohybrid cross is 1 homozygous dominant (AA) : 2 heterozygous (Aa) : 1 homozygous recessive (aa).
49) In humans, brown eyes (B) are dominant over blue eyes (b). What is the genotype of a person who is heterozygous for brown eyes?
a) BB
b) Bb
c) bb
d) bB
Solution: b) Bb
Explanation: A person heterozygous for brown eyes has one dominant allele (B) and one recessive allele (b), so the genotype is Bb.
50) What is the probability of producing a child with blue eyes when both parents are heterozygous for brown eyes?
a) 25%
b) 50%
c) 75%
d) 100%
Solution: a) 25%
Explanation: If both parents are heterozygous (Bb), there’s a 25% chance of producing a child with blue eyes (bb).
51) Which Mendelian law is illustrated by a monohybrid cross?
a) Law of Independent Assortment
b) Law of Segregation
c) Law of Dominance
d) Law of Uniformity
Solution: b) Law of Segregation
Explanation: A monohybrid cross demonstrates Mendel’s Law of Segregation, which states that allele pairs separate during gamete formation.
52) What is indicated by a 3:1 phenotypic ratio in the F2 generation of a typical Mendelian cross?
a) Incomplete dominance
b) Codominance
c) Complete dominance
d) Multiple alleles
Solution: c) Complete dominance
Explanation: A 3:1 phenotypic ratio in the F2 generation suggests complete dominance of one allele over the other.
53) Which genetic phenomenon occurs when neither of two alleles completely masks the other in a heterozygote?
a) Complete dominance
b) Incomplete dominance
c) Codominance
d) Epistasis
Solution: b) Incomplete dominance
Explanation: Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes.
54) If a woman with blood type AB has a child with a man with blood type O, what are the possible blood types of their child?
a) A or B
b) AB or O
c) A, B, or O
d) AB, A, or B
Solution: a) A or B
Explanation: Since the woman is AB and the man is OO, the possible blood types of the child are either A (from the A allele of the mother and the O allele of the father) or B (from the B allele of the mother and the O allele of the father).
55) In a genetic cross, what would be the expected phenotypic ratio of a cross between two plants heterozygous for a trait with incomplete dominance?
a) 1:2:1
b) 3:1
c) 9:3:3:1
d) 1:1
Solution: a) 1:2:1
Explanation: In a cross with incomplete dominance, the phenotypic ratio among offspring is typically 1:2:1 (one homozygous dominant, two heterozygous showing intermediate trait, one homozygous recessive).
56) What is the probability of a child having a recessive trait if one parent is homozygous dominant and the other is heterozygous?
a) 0%
b) 25%
c) 50%
d) 100%
Solution: a) 0%
Explanation: If one parent is homozygous dominant (AA) and the other is heterozygous (Aa), all offspring will have at least one dominant allele, making the expression of a recessive trait impossible.