Inheritance: DNA, Genes, Chromosomes, Mitosis, Meiosis, Monohybrid Crosses and Sex Determination

1. Which statement correctly describes a gene?

A a whole chromosome made only of protein
B a section of DNA that codes for a protein or characteristic
C a sugar molecule found in the cytoplasm
D a cell organelle that controls respiration

2. Which row correctly matches structure and description?

A DNA: made of amino acids
B chromosome: thread-like structure made of DNA and protein
C gene: whole nucleus
D allele: identical copy of every chromosome in the body

3. Which statement about chromosomes in a human body cell is correct?

A it has 23 chromosomes arranged as 23 pairs
B it has 46 chromosomes arranged as 23 pairs
C it has 46 chromosomes arranged as 46 pairs
D it has 23 chromosomes arranged as 46 pairs

4. Which statement about a human sperm cell is correct?

A it is diploid and contains 46 chromosomes
B it is haploid and contains 23 chromosomes
C it is diploid and contains 23 chromosomes
D it is haploid and contains 46 chromosomes

5. Which process produces genetically identical daughter cells for growth and repair?

A meiosis
B fertilisation
C mitosis
D mutation only

6. Which process produces gametes?

A mitosis
B meiosis
C transpiration
D implantation

7. Which statement correctly compares mitosis and meiosis?

A mitosis halves chromosome number; meiosis keeps chromosome number the same
B mitosis produces four genetically different cells; meiosis produces two identical cells
C mitosis produces genetically identical diploid cells; meiosis produces genetically different haploid cells
D mitosis occurs only in gametes; meiosis occurs only in skin cells

8. A diploid cell with 12 chromosomes undergoes mitosis.
   How many chromosomes will each daughter cell have?

A 6
B 12
C 24
D 48

9. A diploid cell with 12 chromosomes undergoes meiosis.
   How many chromosomes will each gamete have?

A 3
B 6
C 12
D 24

10. Which event restores the diploid chromosome number?

A meiosis
B fertilisation
C mitosis
D DNA replication only

11. Which statement about DNA is correct?

A DNA contains a genetic code that can determine the sequence of amino acids in proteins
B DNA is found only in ribosomes
C DNA is made from fatty acids and glycerol
D DNA directly transports oxygen in red blood cells

12. Which structure contains many genes?

A chromosome
B haemoglobin molecule only
C cell wall
D vacuole

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Which statement about alleles is correct?

A alleles are different versions of the same gene
B alleles are different organs in the same body
C alleles are chromosomes from different species only
D alleles are enzymes used in DNA digestion

14. In pea plants, tall stem T is dominant to short stem t.
    Which genotype is heterozygous?

A TT
B Tt
C tt
D TTT

15. Which genotype is homozygous recessive?

A Aa
B AA
C aa
D A

16. Which statement about a dominant allele is correct?

A it is expressed only when two copies are present
B it is expressed in the phenotype when one copy is present
C it is always more common in a population
D it is always beneficial to the organism

17. Which statement about a recessive allele is correct?

A it can be hidden in a heterozygote
B it is always harmful
C it cannot be inherited from parents
D it is expressed whenever a dominant allele is present

18. In guinea pigs, black fur B is dominant to white fur b. Two heterozygous black guinea pigs are crossed.
    What is the expected genotype ratio?

A 1 BB : 2 Bb : 1 bb
B 3 black : 1 white
C 1 Bb : 1 bb
D 2 BB : 2 bb

19. In the same cross, Bb × Bb, what is the expected phenotype ratio?

A 1 black : 2 white
B 3 black : 1 white
C 1 black : 1 white
D 1 black : 3 white

20. A black guinea pig with genotype Bb is crossed with a white guinea pig.
    What proportion of offspring are expected to be white?

A 0%
B 25%
C 50%
D 100%

21. A plant with genotype TT is crossed with a plant with genotype tt.
    What are the genotypes of all offspring?

A TT
B Tt
C tt
D half TT and half tt

22. If all offspring from a cross between a purple-flowered plant and a white-flowered plant are purple, which conclusion is most likely?

A white is dominant and purple is recessive
B purple is dominant and the purple parent may be homozygous
C both parents are homozygous recessive
D the offspring were produced by mitosis only

23. Which cross is a test cross used to find the genotype of an organism showing the dominant phenotype?

A dominant phenotype organism × homozygous recessive organism
B dominant phenotype organism × homozygous dominant organism
C recessive phenotype organism × recessive phenotype organism
D two unknown organisms × each other only

24. A tall plant of unknown genotype is crossed with a short plant. Half the offspring are tall and half are short. Tall is dominant.
    What is the genotype of the unknown tall plant?

A TT
B Tt
C tt
D cannot contain allele T

25. A tall plant of unknown genotype is crossed with a short plant. All offspring are tall. Tall is dominant.
    What is the most likely genotype of the unknown tall plant?

A TT
B Tt
C tt
D impossible to infer anything

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. In rabbits, brown fur B is dominant to white fur b. A brown rabbit and a white rabbit produce one white offspring.
    Which must be true about the brown parent?

A it is BB
B it is Bb
C it is bb
D it has no allele b

27. Which statement about genotype and phenotype is correct?

A genotype is the observable feature; phenotype is the allele combination
B genotype is the allele combination; phenotype is the observable feature
C genotype is always controlled by environment only
D phenotype cannot be affected by genotype

28. Which example shows a phenotype?

A Aa
B BB
C brown eyes
D recessive allele

29. In a monohybrid cross, why are many offspring needed to observe a ratio close to 3:1?

A fertilisation is random, so small sample sizes may not match expected ratios
B dominant alleles always disappear in small samples
C meiosis stops after four offspring
D recessive alleles cannot be inherited repeatedly

30. Which statement about meiosis increases genetic variation?

A it produces cells genetically identical to the parent cell
B it halves chromosome number and produces genetically different gametes
C it stops fertilisation from occurring
D it produces only one type of gamete from each parent

31. A heterozygous organism with genotype Aa produces gametes.
    Which alleles can its gametes contain?

A A only
B a only
C A or a
D Aa in every gamete

32. A homozygous dominant organism with genotype AA produces gametes.
    Which alleles can its gametes contain?

A A only
B a only
C A or a
D AA in every gamete

33. A homozygous recessive organism with genotype aa produces gametes.
    Which alleles can its gametes contain?

A A only
B a only
C A or a
D aa in every gamete

34. In humans, which sex chromosomes are found in most female body cells?

A XX
B XY
C YY
D XO only

35. In humans, which sex chromosomes are found in most male body cells?

A XX
B XY
C YY
D Y only

36. Which gametes can a human female produce with respect to sex chromosomes?

A X only
B Y only
C X or Y
D XX only

37. Which gametes can a human male produce with respect to sex chromosomes?

A X only
B Y only
C X or Y
D XY only

38. What is the expected probability that a child will be male?

A 0%
B 25%
C 50%
D 100%

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Why is the sex of a human baby determined by the sperm cell?

A only sperm cells contain chromosomes
B sperm may carry either X or Y, while ova carry X
C ova carry Y only
D sperm cells are diploid and ova are haploid

40. A human ovum is fertilised by a sperm carrying a Y chromosome.
    What will the sex chromosomes of the zygote be?

A XX
B XY
C YY
D X only

41. A human ovum is fertilised by a sperm carrying an X chromosome.
    What will the sex chromosomes of the zygote be?

A XX
B XY
C YY
D Y only

42. Which statement about sex determination is correct?

A the mother determines sex because ova carry X or Y
B the father determines sex because sperm carry X or Y
C all sperm carry X only
D all ova carry Y only

43. Which cells in humans are normally haploid?

A skin cells
B liver cells
C sperm and ova
D muscle cells

44. Which cells in humans are normally diploid?

A sperm cells only
B ova only
C body cells
D gametes only

45. Which statement about mutation is correct?

A mutation is a change in DNA
B mutation always improves survival
C mutation always occurs during fertilisation only
D mutation is the same as mitosis

46. Which outcome of mutation is possible?

A it may be harmful, beneficial or have no effect
B it always creates a new species immediately
C it always changes every chromosome in every body cell
D it prevents all inheritance

47. Which statement about inherited characteristics is correct?

A inherited characteristics are passed through genes from parents to offspring
B inherited characteristics are always caused only by diet
C inherited characteristics cannot be affected by alleles
D inherited characteristics are passed through blood plasma

48. Which statement about discontinuous variation is correct?

A individuals fall into distinct categories with no intermediates
B individuals show a continuous range of values
C it is always caused only by environment
D height is the best example because it has no intermediates

49. Which statement about mitosis is correct?

A it produces variation by forming gametes
B it maintains chromosome number and produces identical cells
C it halves chromosome number from diploid to haploid
D it produces four daughter cells from one parent cell

50. Which statement is correct?

A meiosis produces haploid gametes, and fertilisation restores diploid chromosome number
B mitosis produces haploid gametes, and fertilisation halves chromosome number
C chromosomes are made of glucose and stored only in the cytoplasm
D genes are formed only after fertilisation and disappear before birth

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. Answer: B
   A is wrong because a chromosome is made of DNA and protein, not a gene itself.
   B is correct because a gene is a section of DNA that codes for a protein or characteristic.
   C is wrong because sugar molecules are part of nucleotides, not genes.
   D is wrong because organelles such as mitochondria control respiration, not genes.

2. Answer: B
   A is wrong because DNA is made of nucleotides, not amino acids.
   B is correct because chromosomes are thread-like structures made of DNA and protein.
   C is wrong because a gene is a section of DNA, not the whole nucleus.
   D is wrong because an allele is a version of a gene, not a complete chromosome copy.

3. Answer: B
   A is wrong because 23 chromosomes is the haploid number in human gametes.
   B is correct because a human body cell has 46 chromosomes arranged in 23 pairs.
   C is wrong because 46 pairs would mean 92 chromosomes.
   D is wrong because 23 chromosomes cannot form 46 pairs.

4. Answer: B
   A is wrong because sperm are not diploid.
   B is correct because a human sperm cell is haploid and contains 23 chromosomes.
   C is wrong because diploid cells in humans contain 46 chromosomes.
   D is wrong because 46 chromosomes is the diploid number, not haploid.

5. Answer: C
   A is wrong because meiosis produces gametes and variation.
   B is wrong because fertilisation fuses gametes.
   C is correct because mitosis produces genetically identical daughter cells for growth, repair and asexual reproduction.
   D is wrong because mutation is a change in DNA, not normal cell division for growth.

6. Answer: B
   A is wrong because mitosis produces identical body cells.
   B is correct because meiosis produces gametes.
   C is wrong because transpiration is water loss from plants.
   D is wrong because implantation is embryo attachment to the uterus lining.

7. Answer: C
   A is wrong because mitosis maintains chromosome number; meiosis halves it.
   B is wrong because mitosis usually produces two identical cells, while meiosis produces four different cells.
   C is correct because mitosis produces genetically identical diploid cells, while meiosis produces genetically different haploid cells.
   D is wrong because meiosis occurs in reproductive organs to form gametes; mitosis occurs in body cells.

8. Answer: B
   A is wrong because 6 chromosomes would be produced after meiosis, not mitosis.
   B is correct because mitosis keeps the chromosome number the same, so each daughter cell has 12 chromosomes.
   C is wrong because chromosome number does not double in the final daughter cells.
   D is wrong because 48 is far too high.

9. Answer: B
   A is wrong because meiosis halves 12 to 6, not 3.
   B is correct because meiosis halves the chromosome number, so gametes have 6 chromosomes.
   C is wrong because 12 would be unchanged, like mitosis.
   D is wrong because 24 would be double the original number.

10. Answer: B
    A is wrong because meiosis halves the chromosome number.
    B is correct because fertilisation fuses two haploid gametes and restores the diploid chromosome number.
    C is wrong because mitosis maintains chromosome number but does not restore diploid number from gametes.
    D is wrong because DNA replication copies DNA before cell division but does not fuse gametes.

11. Answer: A
    A is correct because DNA contains a genetic code that determines the amino acid sequence in proteins.
    B is wrong because DNA is mainly found in the nucleus, not only ribosomes.
    C is wrong because lipids are made from fatty acids and glycerol.
    D is wrong because haemoglobin transports oxygen.

12. Answer: A
    A is correct because chromosomes contain many genes.
    B is wrong because haemoglobin is a protein, not the structure carrying many genes.
    C is wrong because a cell wall is mainly cellulose in plants.
    D is wrong because a vacuole contains cell sap.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Answer: A
    A is correct because alleles are different versions of the same gene.
    B is wrong because organs are body structures, not versions of genes.
    C is wrong because alleles are not chromosomes from different species.
    D is wrong because alleles are not enzymes.

14. Answer: B
    A is wrong because TT is homozygous dominant.
    B is correct because Tt has two different alleles, so it is heterozygous.
    C is wrong because tt is homozygous recessive.
    D is wrong because TTT is not the normal diploid genotype format for one gene.

15. Answer: C
    A is wrong because Aa is heterozygous.
    B is wrong because AA is homozygous dominant.
    C is correct because aa has two recessive alleles.
    D is wrong because one allele alone does not show a diploid genotype.

16. Answer: B
    A is wrong because that describes a recessive allele.
    B is correct because a dominant allele is expressed even when only one copy is present.
    C is wrong because dominant does not mean more common.
    D is wrong because dominant does not mean beneficial.

17. Answer: A
    A is correct because a recessive allele can be hidden when a dominant allele is also present.
    B is wrong because recessive alleles are not always harmful.
    C is wrong because recessive alleles can be inherited.
    D is wrong because a recessive allele is usually not expressed when a dominant allele is present.

18. Answer: A
    Bb × Bb gives BB, Bb, Bb, bb.
    A is correct because the genotype ratio is 1 BB : 2 Bb : 1 bb.
    B is wrong because that is the phenotype ratio, not genotype ratio.
    C is wrong because that ratio comes from Bb × bb.
    D is wrong because heterozygous offspring are missing.

19. Answer: B
    Bb × Bb gives 3 black offspring and 1 white offspring because B is dominant.
    A is wrong because it gives too many white offspring.
    B is correct: 3 black : 1 white.
    C is wrong because 1:1 would come from Bb × bb.
    D is wrong because black is dominant, not white.

20. Answer: C
    Bb × bb gives Bb, bb, Bb, bb.
    A is wrong because white offspring can occur.
    B is wrong because 25% would come from two heterozygotes producing recessive phenotype.
    C is correct because 50% are expected to be bb white.
    D is wrong because half, not all, are white.

21. Answer: B
    TT produces only T gametes; tt produces only t gametes.
    A is wrong because offspring receive one T and one t, not two T alleles.
    B is correct because all offspring are Tt.
    C is wrong because all offspring have the dominant T allele.
    D is wrong because offspring are not TT or tt.

22. Answer: B
    A is wrong because if white were dominant, all offspring would not necessarily be purple.
    B is correct because if all offspring are purple, purple is most likely dominant and the purple parent may be homozygous.
    C is wrong because homozygous recessive parents cannot produce dominant purple offspring.
    D is wrong because flowering plant offspring from this cross are produced sexually, not by mitosis only.

23. Answer: A
    A is correct because a test cross uses a homozygous recessive organism to reveal the genotype of the dominant phenotype organism.
    B is wrong because crossing with homozygous dominant can hide the unknown genotype.
    C is wrong because two recessive organisms do not test a dominant phenotype organism.
    D is too vague and not the definition.

24. Answer: B
    Tall unknown × short tt gives half tall and half short. This means unknown tall must produce T and t gametes.
    A is wrong because TT × tt would give all tall.
    B is correct because Tt × tt gives 1 tall : 1 short.
    C is wrong because tt would be short, not tall.
    D is wrong because a tall plant must contain at least one T allele.

25. Answer: A
    Tall unknown × short tt gives all tall.
    A is correct because TT × tt gives all Tt tall offspring.
    B is wrong because Tt × tt would give some short offspring.
    C is wrong because tt is short.
    D is wrong because the result strongly suggests the tall parent is TT.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. Answer: B
    A is wrong because BB crossed with bb would produce all Bb brown offspring, no white.
    B is correct because the brown parent must have a recessive b allele to produce a white bb offspring.
    C is wrong because bb would be white, not brown.
    D is wrong because the brown parent must contain allele b.

27. Answer: B
    A is wrong because it reverses genotype and phenotype.
    B is correct because genotype is the allele combination, while phenotype is the observable feature.
    C is wrong because genotype is inherited alleles, not environment only.
    D is wrong because phenotype is strongly affected by genotype, although environment may also affect it.

28. Answer: C
    A is wrong because Aa is a genotype.
    B is wrong because BB is a genotype.
    C is correct because brown eyes are an observable feature, so this is a phenotype.
    D is wrong because “recessive allele” describes an allele type, not an observable feature.

29. Answer: A
    A is correct because fertilisation is random, so small samples may not match expected ratios closely.
    B is wrong because dominant alleles do not disappear in small samples.
    C is wrong because meiosis does not stop after four offspring.
    D is wrong because recessive alleles can be inherited repeatedly.

30. Answer: B
    A is wrong because genetically identical cells are produced by mitosis.
    B is correct because meiosis halves chromosome number and produces genetically different gametes.
    C is wrong because meiosis prepares for fertilisation; it does not stop it.
    D is wrong because meiosis can produce different types of gametes.

31. Answer: C
    A is wrong because a heterozygote can pass on A or a.
    B is wrong because it can also pass on A.
    C is correct because gametes from Aa contain either A or a.
    D is wrong because gametes are haploid and carry one allele for the gene, not Aa.

32. Answer: A
    A is correct because AA can only produce gametes carrying A.
    B is wrong because no a allele is present.
    C is wrong because only A can be passed on.
    D is wrong because gametes carry one allele, not AA.

33. Answer: B
    A is wrong because no A allele is present.
    B is correct because aa can only produce gametes carrying a.
    C is wrong because only a can be passed on.
    D is wrong because gametes carry one allele, not aa.

34. Answer: A
    A is correct because most female body cells contain XX sex chromosomes.
    B is wrong because XY is male.
    C is wrong because YY is not a normal human sex chromosome combination.
    D is wrong because XO is not the normal female body cell combination.

35. Answer: B
    A is wrong because XX is female.
    B is correct because most male body cells contain XY sex chromosomes.
    C is wrong because YY is not a normal human sex chromosome combination.
    D is wrong because male body cells have both X and Y, not Y only.

36. Answer: A
    A is correct because human females are XX, so ova carry X only.
    B is wrong because females do not have a Y chromosome to pass on.
    C is wrong because X or Y gametes are produced by males.
    D is wrong because ova are haploid and carry one X, not XX.

37. Answer: C
    A is wrong because males can also produce Y-bearing sperm.
    B is wrong because males can also produce X-bearing sperm.
    C is correct because human males are XY, so sperm may carry X or Y.
    D is wrong because sperm are haploid and carry one sex chromosome, not XY.

38. Answer: C
    A is wrong because male children can be born.
    B is wrong because the expected probability is not 25%.
    C is correct because there is roughly a 50% chance of an X sperm and 50% chance of a Y sperm fertilising the ovum.
    D is wrong because not all children are male.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Answer: B
    A is wrong because both sperm and ova contain chromosomes.
    B is correct because sperm may carry X or Y, while ova carry X only.
    C is wrong because ova carry X only.
    D is wrong because both sperm and ova are haploid.

40. Answer: B
    A is wrong because XX results from an X sperm fertilising an X ovum.
    B is correct because an X ovum fertilised by a Y sperm gives XY.
    C is wrong because the ovum contributes X, not Y.
    D is wrong because the zygote has two sex chromosomes.

41. Answer: A
    A is correct because an X ovum fertilised by an X sperm gives XX.
    B is wrong because XY requires a Y sperm.
    C is wrong because the ovum contributes X, not Y.
    D is wrong because the zygote has two sex chromosomes.

42. Answer: B
    A is wrong because ova carry X only.
    B is correct because sperm carry either X or Y, so the father’s sperm determines sex.
    C is wrong because not all sperm carry X.
    D is wrong because ova do not carry Y.

43. Answer: C
    A is wrong because skin cells are diploid body cells.
    B is wrong because liver cells are diploid body cells.
    C is correct because sperm and ova are haploid gametes.
    D is wrong because muscle cells are diploid body cells.

44. Answer: C
    A is wrong because sperm cells are haploid.
    B is wrong because ova are haploid.
    C is correct because body cells are normally diploid.
    D is wrong because gametes are haploid.

45. Answer: A
    A is correct because mutation is a change in DNA.
    B is wrong because mutations can be harmful, beneficial or neutral.
    C is wrong because mutations can occur at different times, not only during fertilisation.
    D is wrong because mutation is not cell division.

46. Answer: A
    A is correct because a mutation may be harmful, beneficial or have no effect.
    B is wrong because mutation does not always create a new species immediately.
    C is wrong because a mutation may affect one gene or cell, not necessarily every chromosome in every body cell.
    D is wrong because mutation does not prevent all inheritance.

47. Answer: A
    A is correct because inherited characteristics are passed from parents to offspring through genes.
    B is wrong because diet affects acquired/environmental characteristics, not inherited ones only.
    C is wrong because alleles affect inherited characteristics.
    D is wrong because inherited information is passed through gametes, not blood plasma.

48. Answer: A
    A is correct because discontinuous variation has distinct categories with no intermediates.
    B is wrong because a continuous range describes continuous variation.
    C is wrong because discontinuous variation is usually mainly genetic, not always environment only.
    D is wrong because height is continuous variation with intermediates.

49. Answer: B
    A is wrong because meiosis produces gametes and variation.
    B is correct because mitosis maintains chromosome number and produces genetically identical cells.
    C is wrong because meiosis halves chromosome number.
    D is wrong because meiosis produces four daughter cells; mitosis produces two.

50. Answer: A
    A is correct because meiosis produces haploid gametes, and fertilisation restores diploid chromosome number.
    B is wrong because mitosis does not produce haploid gametes.
    C is wrong because chromosomes are made of DNA and protein, not glucose, and are found in the nucleus.
    D is wrong because genes exist before fertilisation and do not disappear before birth.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.