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O Level Biology: Inheritance MCQs — Biology

30 multiple-choice questions on O Level Biology: Inheritance from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Natural selection leads to

  1. loss of all variation instantly
  2. identical offspring
  3. evolution of inherited features over time
  4. immediate change in one individual

Answer: C) evolution of inherited features over time

Explanation: Populations change over generations. O Level Biology · Topic 17 Inheritance · 17.4 Selection

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2. A person with blood group AB has genotype

  1. IᴮIᴼ
  2. IᴼIᴼ
  3. IᴬIᴼ
  4. IᴬIᴮ

Answer: D) IᴬIᴮ

Explanation: AB results from codominance. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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3. What is the chance that a baby will be a boy?

  1. 100%
  2. 75%
  3. 50%
  4. 25%

Answer: C) 50%

Explanation: Half the sperm carry Y. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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4. Sickle cell anaemia is an example of

  1. a chromosome mutation
  2. a gene mutation
  3. codominance only
  4. natural selection only

Answer: B) a gene mutation

Explanation: A base change in the haemoglobin gene. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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5. In DNA, adenine always pairs with

  1. guanine
  2. uracil
  3. thymine
  4. cytosine

Answer: C) thymine

Explanation: A–T and C–G. O Level Biology · Topic 17 Inheritance · 17.2 DNA

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6. DNA controls cell activities by controlling the production of

  1. lipids only
  2. carbohydrates only
  3. water
  4. proteins, including enzymes

Answer: D) proteins, including enzymes

Explanation: Enzymes made from DNA instructions control reactions. O Level Biology · Topic 17 Inheritance · 17.2 DNA

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7. In natural selection, the organisms that survive are those that

  1. are better adapted to their environment
  2. are the largest
  3. are the youngest
  4. reproduce asexually

Answer: A) are better adapted to their environment

Explanation: Best adapted survive and reproduce. O Level Biology · Topic 17 Inheritance · 17.4 Selection

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8. Selective breeding involves

  1. humans choosing individuals with desirable features to breed
  2. inserting genes from other species
  3. the environment choosing the fittest
  4. cloning by mitosis only

Answer: A) humans choosing individuals with desirable features to breed

Explanation: Artificial selection is done by humans. O Level Biology · Topic 17 Inheritance · 17.4 Selection

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9. The sequence of bases in a gene determines

  1. the size of the cell
  2. the sequence of amino acids in a protein
  3. the type of sugar
  4. the number of chromosomes

Answer: B) the sequence of amino acids in a protein

Explanation: Bases code for amino acids. O Level Biology · Topic 17 Inheritance · 17.2 DNA

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10. Down's syndrome is caused by

  1. a gene mutation in haemoglobin
  2. an extra chromosome 21, giving 47 chromosomes
  3. a missing X chromosome
  4. a virus

Answer: B) an extra chromosome 21, giving 47 chromosomes

Explanation: A chromosome mutation. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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11. Expected ratios in a cross are often not seen exactly because

  1. fertilisation is random and numbers are small
  2. mutations always happen
  3. the parents are always homozygous
  4. genes change during the cross

Answer: A) fertilisation is random and numbers are small

Explanation: Chance matters with small samples. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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12. One DNA strand has the base sequence ACGT. The complementary strand is

  1. GTAC
  2. CATG
  3. ACGT
  4. TGCA

Answer: D) TGCA

Explanation: A↔T, C↔G. O Level Biology · Topic 17 Inheritance · 17.2 DNA

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13. Parents IᴬIᴼ and IᴮIᴼ can have a child with blood group

  1. only AB
  2. only O
  3. A, B, AB or O
  4. only A or B

Answer: C) A, B, AB or O

Explanation: All four combinations are possible. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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14. Which increases the rate of mutation?

  1. Ionising radiation
  2. Exercise
  3. Fresh water
  4. Vitamins

Answer: A) Ionising radiation

Explanation: Radiation damages DNA. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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15. Two heterozygous tall plants (Tt × Tt) are crossed. What ratio of tall to short is expected?

  1. 3 : 1
  2. 1 : 2 : 1 tall only
  3. 1 : 1
  4. all tall

Answer: A) 3 : 1

Explanation: TT, Tt, Tt are tall; tt is short. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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16. Continuous variation is usually caused by

  1. genes only
  2. environment only
  3. both genes and the environment
  4. mutation only

Answer: C) both genes and the environment

Explanation: Many genes plus environment. O Level Biology · Topic 17 Inheritance · 17.1 Variation

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17. A heterozygous plant is crossed with a homozygous recessive plant. The expected ratio is

  1. all dominant
  2. 1 : 2 : 1
  3. 3 : 1
  4. 1 : 1

Answer: D) 1 : 1

Explanation: Tt × tt gives half Tt, half tt. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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18. A gene is

  1. a length of DNA that codes for a protein
  2. a whole chromosome
  3. an amino acid
  4. a type of cell

Answer: A) a length of DNA that codes for a protein

Explanation: Definition of a gene. O Level Biology · Topic 17 Inheritance · 17.2 DNA

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19. A recessive allele is expressed only when

  1. it is on the Y chromosome
  2. one dominant allele is present
  3. no dominant allele is present
  4. the organism is heterozygous

Answer: C) no dominant allele is present

Explanation: Recessive shows only in homozygous recessives. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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20. Which is the correct order of events in natural selection?

  1. competition → mutation → death of all → reproduction
  2. survival → variation → competition → overproduction
  3. variation → overproduction → competition → survival of the best adapted → alleles passed on
  4. overproduction → death of the best adapted → variation

Answer: C) variation → overproduction → competition → survival of the best adapted → alleles passed on

Explanation: Darwin's sequence. O Level Biology · Topic 17 Inheritance · 17.4 Selection

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21. An allele is

  1. an alternative form of a gene
  2. a gamete
  3. a protein
  4. a type of chromosome

Answer: A) an alternative form of a gene

Explanation: Definition of allele. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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22. An organism with genotype Tt is

  1. heterozygous
  2. homozygous recessive
  3. pure-breeding
  4. homozygous dominant

Answer: A) heterozygous

Explanation: Two different alleles. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

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23. Variation is

  1. differences between species
  2. differences between individuals of the same species
  3. changes in the environment
  4. a type of reproduction

Answer: B) differences between individuals of the same species

Explanation: Definition of variation. O Level Biology · Topic 17 Inheritance · 17.1 Variation

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24. Which graph is used for continuous variation data?

  1. Line graph of time
  2. Pie chart only
  3. Bar chart with gaps
  4. Histogram

Answer: D) Histogram

Explanation: Grouped data in a histogram. O Level Biology · Topic 17 Inheritance · 17.1 Variation

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25. Which is an example of artificial selection?

  1. Mosquitoes resistant to insecticides
  2. Breeding cows that give more milk
  3. Peppered moths becoming darker
  4. Bacteria becoming resistant to antibiotics

Answer: B) Breeding cows that give more milk

Explanation: Farmers choose high-yielding cattle. O Level Biology · Topic 17 Inheritance · 17.4 Selection

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