Free Inheritance MCQs with Answers
1,238 Inheritance MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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41. A male expresses an X linked recessive trait whenever he inherits one recessive allele because he
- A. has only one X chromosome
- B. has two Y chromosomes
- C. inactivates the normal allele
- D. lacks the gene altogether
Explanation: With no second X to supply a dominant allele, the single recessive allele has nothing to mask it, a state called hemizygosity.
Correct answer: has only one X chromosome- A. None
- B. Half
- C. A quarter
- D. All of them
Explanation: The woman must be a carrier since she inherited her affected father's X.
Correct answer: Half- A. was cured by royal physicians
- B. is common in every royal family
- C. was traced through the descendants of Queen Victoria
- D. was first described by a king
Explanation: Victoria carried the allele and passed it into the royal houses of Russia and Spain, producing affected princes across Europe.
Correct answer: was traced through the descendants of Queen Victoria- A. from mother to sons
- B. from father to all his sons
- C. equally to sons and daughters
- D. to daughters only
Explanation: Only males carry a Y chromosome, and a father passes it to every son and no daughter, so Y linked traits run strictly down the male line.
Correct answer: to daughters only- A. Red green colour blindness
- B. Sickle cell anaemia
- C. Down syndrome
- D. Albinism
Explanation: The genes for red and green pigments lie on the X chromosome, so colour blindness follows the X linked pattern.
Correct answer: Red green colour blindness- A. a man suffering from the disease
- B. a heterozygous woman with one normal and one haemophilia allele
- C. a homozygous normal woman
- D. a person with an extra chromosome
Explanation: A carrier holds the recessive allele without symptoms because the normal allele on her other X is enough for clotting.
Correct answer: a heterozygous woman with one normal and one haemophilia allele- A. zero
- B. one quarter
- C. one half
- D. certain
Explanation: The woman inherited her haemophiliac father's X, making her a carrier. She passes that X to half her sons, who will be affected, and the…
Correct answer: one half48. In the cells of a female mammal, one of the two X chromosomes condenses into a dense body called the
- A. centromere
- B. nucleolus
- C. chiasma
- D. Barr body
Explanation: The inactivated X, or Barr body, equalises the gene dose between XX females and XY males.
Correct answer: Barr body- A. Alleles separate during gamete formation
- B. Different genes assort independently
- C. Dominant alleles always mask recessive
- D. Genes are on chromosomes
Explanation: The law of segregation states that allele pairs separate during gamete formation, so each gamete carries one allele.
Correct answer: Alleles separate during gamete formation- A. The genotype of a dominant phenotype individual
- B. The number of chromosomes
- C. Mutation rates
- D. Linkage groups
Explanation: A test cross between an individual showing dominant phenotype and a homozygous recessive reveals whether the dominant is homozygous or…
Correct answer: The genotype of a dominant phenotype individual- A. Only dominant phenotype
- B. Only recessive phenotype
- C. Intermediate phenotype
- D. Both phenotypes expressed
Explanation: In incomplete dominance, the heterozygote shows an intermediate phenotype, e.g., pink flowers from red and white parents.
Correct answer: Intermediate phenotype- A. Complete dominance only
- B. Incomplete dominance
- C. Codominance and multiple alleles
- D. Sex linkage
Explanation: ABO system shows codominance (IA and IB both expressed in AB) and multiple alleles (IA, IB, i).
Correct answer: Codominance and multiple alleles53. Haemophilia is
- A. Autosomal dominant
- B. Autosomal recessive
- C. X-linked recessive
- D. Y-linked
Explanation: Haemophilia is an X-linked recessive disorder affecting blood clotting, more common in males.
Correct answer: X-linked recessive- A. Increases with distance on chromosome
- B. Decreases with distance
- C. Is unaffected by distance
- D. Only occurs on sex chromosomes
Explanation: Linkage decreases with distance; genes farther apart cross over more frequently. 1% recombination = 1 map unit.
Correct answer: Decreases with distance- A. Heterozygote frequency
- B. Homozygous dominant frequency
- C. Homozygous recessive frequency
- D. Total alleles
Explanation: p² = frequency of homozygous dominant (AA), 2pq = heterozygous (Aa), q² = homozygous recessive (aa).
Correct answer: Homozygous dominant frequency- A. One gene with two alleles
- B. Multiple genes affecting one trait
- C. Genes on sex chromosomes only
- D. Mitochondrial genes
Explanation: Polygenic traits (height, skin color) are controlled by multiple genes, showing continuous variation.
Correct answer: Multiple genes affecting one trait- A. Male with the disorder
- B. Female with one affected X
- C. Female with both X affected
- D. Male without the disorder
Explanation: Carrier females are heterozygous (XAXa) and phenotypically normal but can pass the allele to offspring.
Correct answer: Female with one affected X- A. One gene affecting multiple traits
- B. Multiple genes affecting one trait
- C. Genes on same chromosome
- D. Genes affecting only one tissue
Explanation: Pleiotropy is when one gene affects multiple phenotypic traits, e.g., sickle cell gene affects multiple organs.
Correct answer: One gene affecting multiple traits- A. Genetic drift
- B. Small population
- C. Gene linkage
- D. Gene duplication
Explanation: Independent assortment requires the two genes to be on different chromosomes, so genes linked on the same chromosome travel together and…
Correct answer: Gene linkage- A. Duplication of chromosome
- B. Exchange of genes between non-sister chromatids
- C. Movement of chromosome to opposite poles
- D. Separation of sister chromatids
Explanation: During prophase I the homologues pair as bivalents and non sister chromatids exchange equal segments at chiasmata, producing chromosomes…
Correct answer: Exchange of genes between non-sister chromatids