Gene Linkage and Crossing Over

Gene Linkage and Crossing Over MDCAT MCQs with answers

26 past paper MCQs on Gene Linkage and Crossing Over, from the Inheritance unit of MDCAT Biology. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.The 9.3.3.1 ratio of law of Independent assortment can be affected by (UHS MDCAT 2025)

  1. Genetic drift
  2. Small population
  3. Gene linkage
  4. Gene duplication
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Correct answer: (c) Gene linkage

Genes on the same chromosome are inherited together, so linkage upsets the 9:3:3:1 ratio independent assortment predicts.

2.Best description of the process of crossing over during meiosis: (UHS MDCAT 2025)

  1. Duplication of chromosome
  2. Exchange of genes between non-sister chromatids
  3. Movement of chromosome to opposite poles
  4. Separation of sister chromatids
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Correct answer: (b) Exchange of genes between non-sister chromatids

Crossing over is the exchange of segments between non-sister chromatids of homologous chromosomes at prophase I.

3.Total number of linkage groups in a normal human is: (UHS MDCAT 2025)

  1. 02
  2. 23
  3. 46
  4. 92
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Correct answer: (b) 23

A linkage group is one chromosome of a haploid set, and the human haploid number is 23.

4.In crossing over, an exchange of maternal and paternal chromatid parts occurs while homologous chromosomes are paired _____ stage of meiosis. (KMU MDCAT 2025)

  1. Metaphase I
  2. Prophase I
  3. Anaphase II
  4. Telophase I
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Correct answer: (b) Prophase I

Homologues pair and exchange segments at prophase I, in the pachytene of that stage.

5.Linked genes DO NOT follow Mendel's Law of Independent Assortment because (KMU MDCAT 2025)

  1. They are located on different chromosomes
  2. They always undergo crossing over
  3. They are physically close together on the same chromosome
  4. They rarely separate during meiosis
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Correct answer: (c) They are physically close together on the same chromosome

Genes close together on one chromosome travel together, so they cannot assort independently.

6.The phenomena of gene linkage rejects the concept of: (NUMS MDCAT 2025)

  1. Law of segregation
  2. Polygenic traits
  3. Epistasis
  4. Law of independent assortment
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Correct answer: (d) Law of independent assortment

Linked genes travel together, so they cannot assort independently.

7.Which of the following is used to determine linkage between two gene pairs? (NUMS MDCAT 2025)

  1. Test cross
  2. Back cross
  3. Monohybrid cross
  4. Dihybrid cross
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Correct answer: (a) Test cross

Crossing the heterozygote with the double recessive shows the parental types directly, which reveals linkage.

8.Crossing over involves exchange of genetic material between: (SIBA MDCAT 2025)

  1. Sister chromatids of same chromosome
  2. Non-sister chromatids of homologous chromosomes
  3. Chromatids of non-homologous chromosomes
  4. Sister chromatids of homologous chromosomes
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Correct answer: (b) Non-sister chromatids of homologous chromosomes

Segments are swapped between non-sister chromatids of a homologous pair.

9.Linkage of genes in Drosophila was first discovered by: (SIBA MDCAT 2025)

  1. Thomas Hunt Morgan
  2. Alfred Sturtevant
  3. Gregor Mendel
  4. Hugo de Vries
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Correct answer: (a) Thomas Hunt Morgan

Morgan found linkage while breeding the fruit fly Drosophila melanogaster.

10.Which phenomenon increases the chances of variations? (SIBA MDCAT 2025)

  1. Crossing Over
  2. Linkage
  3. Epistasis
  4. Dominance
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Correct answer: (a) Crossing Over

Crossing over recombines the alleles of a chromosome, so it makes new combinations.

11.When genes are linked, they tend to: (SZABMU MDCAT 2025)

  1. Segregate randomly
  2. Cross over every time
  3. Stay together during inheritance
  4. Be inherited separately
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Correct answer: (c) Stay together during inheritance

Genes on one chromosome are carried together into the same gamete.

12.According to Morgan's experiment, which of the following is essential for detecting gene linkage accurately? (SZABMU MDCAT 2025)

  1. Large number of progeny
  2. Small sample size
  3. Use of male flies only
  4. Mutation induction
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Correct answer: (a) Large number of progeny

Recombinants are a small fraction, so a large brood is needed before the ratio means anything.

13.What is the primary outcome of crossing over during prophase of meiosis I? (KMU MDCAT 2024)

  1. Chromosomes duplicate without any exchange of parts
  2. Homologous chromosomes exchange different pairs leading to recombinant chromatids and increased genetic variation
  3. Homologous chromosomes exchange identical parts, resulting in no genetic variation
  4. Non-homologous chromosomes exchange part
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Correct answer: (b) Homologous chromosomes exchange different pairs leading to recombinant chromatids and increased genetic variation

Homologues swap segments, so the chromatids that result carry new combinations of alleles.

14.These are the genes which tend to be inherited together and do not assort independently: (SZABMU MDCAT 2023)

  1. Linked genes
  2. Dependent genes
  3. Recombinant genes
  4. Independent genes
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Correct answer: (a) Linked genes

Genes on the same chromosome are linked and travel together.

15.Linkage reduces the frequency of: (PMC MDCAT 2022)

  1. Recombinants or hybrids
  2. Parental phenotypes
  3. Dominant homozygotes
  4. Recessive homozygotes
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Correct answer: (a) Recombinants or hybrids

Linked genes travel together, so few recombinant gametes are made.

16.Crossing over brings: (PMC MDCAT 2022)

  1. recombination of genes
  2. New trait into species
  3. Reduction in number of chromosomes
  4. Segregation of genes
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Correct answer: (a) recombination of genes

Crossing over exchanges segments between homologues, so the chromatids carry new combinations.

17.One map unit is supposed to be equal to: (PMC MDCAT 2022)

  1. 1%recombination frequency
  2. 5%recombination frequency
  3. 10%recombination frequency
  4. 15%recombination frequency
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Correct answer: (a) 1%recombination frequency

A map unit, or centimorgan, is one per cent recombination.

18.In Morgan’s linkage experiment, when males and females of F2 generation mate with each other and produce offspring, the percentage of recombinants was: (PMC Practice 2021)

  1. 37
  2. 22
  3. 2
  4. 70
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Correct answer: (a) 37

Morgan found about $37\%$ recombinants, well below the fifty per cent independent assortment would give.

19.The process of determining the locus for particular biological traits includes? (PMC Practice 2021)

  1. Replication
  2. Recombination
  3. Gene mapping
  4. None of these options is correct
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Correct answer: (c) Gene mapping

Working out where a gene lies on its chromosome is gene mapping.

20.During meiosis, the homologous chromosomes come together and form pairs, this process is called: (PMC MDCAT 2020)

  1. Linkage
  2. Synapsis
  3. Pairing
  4. Crossing over
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Correct answer: (b) Synapsis

The pairing of homologues at prophase I is synapsis.

21.In which situation are genes, are not assorted independently, during meiosis in a chromosome? (UHS MDCAT 2019)

  1. When genes are linked and their loci are close to each other
  2. When some genes have mutated on the chromosome
  3. When there are too many Genes on a chromosome
  4. When genes are not linked and their loci are far apart
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Correct answer: (a) When genes are linked and their loci are close to each other

Genes close together on one chromosome are carried into the same gamete.

22.In genetics, the term locus refers to the ______ of the gene on the chromosome. (UHS MDCAT 2019)

  1. Position
  2. Frequency
  3. Copy
  4. Inversion
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Correct answer: (a) Position

The place a gene occupies on its chromosome is its locus.

23.Chance of a cross over between two loci is directly proportional to their (UHS MDCAT 2018)

  1. Thickens
  2. Width
  3. Length
  4. Distance
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Correct answer: (d) Distance

The further apart two loci lie, the likelier a chiasma falls between them.

24.There are ______ number of linkage groups in humans. (UHS MDCAT 2018)

  1. 46
  2. 22
  3. 80
  4. 23
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Correct answer: (d) 23

A linkage group is one chromosome of a haploid set, and the human haploid number is 23.

25._________ is the exact position of a gene on the chromosome. (UHS MDCAT 2018)

  1. Trait
  2. Centromere
  3. Genotype
  4. Locus
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Correct answer: (d) Locus

The place a gene occupies on the chromosome is its locus.

26.Crossing over takes place during _____ of meiosis. (UHS MDCAT 2018)

  1. Prophase I
  2. Telophase I
  3. Metaphase I
  4. Anaphase I
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Correct answer: (a) Prophase I

Homologues pair and exchange segments at prophase I.

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