Part 4: Linkage and Crossing Over – MCQs
Part 4: Linkage and Crossing Over (25 MCQs)
Q76. Linkage refers to:
a) Independent inheritance of genes
b) Tendency of genes on the same chromosome to be inherited together
c) Exchange of chromosome segments
d) Mutation in chromosomes
Answer: b
- b) Correct: Linkage = genes on the same chromosome tend to be inherited together.
- a) Independent assortment is the opposite.
- c) That’s crossing over.
- d) Not related.
Q77. Who first discovered linkage?
a) Mendel
b) Sutton
c) Morgan
d) Bateson and Punnett
Answer: d
- d) Correct: Bateson and Punnett discovered linkage in sweet pea (Lathyrus).
- c) Morgan later explained linkage using Drosophila.
Q78. Experimental proof of linkage was given by:
a) Bateson
b) Morgan
c) Punnett
d) Sutton
Answer: b
- b) Correct: Morgan proved linkage in Drosophila.
Q79. Genes located close together on a chromosome show:
a) High recombination
b) Low recombination
c) Independent assortment
d) Mutation
Answer: b
- b) Correct: Closer genes → less crossing over → low recombination.
Q80. Which of the following explains recombination frequency?
a) 0% for linked genes
b) Higher when genes are far apart
c) Always 50%
d) Not related to distance
Answer: b
- b) Correct: Greater distance → more crossing over → higher recombination frequency.
Q81. Maximum recombination frequency between two genes is:
a) 10%
b) 25%
c) 50%
d) 100%
Answer: c
- c) Correct: Maximum = 50% (beyond that, genes behave as if on different chromosomes).
Q82. Who coined the term “crossing over”?
a) Morgan
b) Bateson
c) Sutton
d) Bridges
Answer: a
- a) Correct: Morgan coined crossing over.
Q83. Crossing over occurs during:
a) Prophase I of meiosis
b) Prophase II of meiosis
c) Anaphase I
d) Metaphase II
Answer: a
- a) Correct: Crossing over = exchange of chromatid segments in prophase I (pachytene stage).
Q84. The exchange of segments between non-sister chromatids of homologous chromosomes is called:
a) Linkage
b) Mutation
c) Crossing over
d) Nondisjunction
Answer: c
- c) Correct: Definition of crossing over.
Q85. Who gave cytological proof of crossing over?
a) Morgan
b) Bridges
c) Sturtevant
d) Creighton and McClintock
Answer: d
- d) Correct: Creighton and McClintock (maize) → cytological proof of crossing over.
Q86. Crossing over results in:
a) Linkage
b) Genetic recombination
c) Mutation
d) Polyploidy
Answer: b
- b) Correct: Crossing over produces new gene combinations → genetic recombination.
Q87. Which of the following reduces linkage?
a) Crossing over
b) Mutation
c) Nondisjunction
d) Replication
Answer: a
- a) Correct: Crossing over breaks linkage.
Q88. In complete linkage, recombination frequency is:
a) 0%
b) 25%
c) 50%
d) 100%
Answer: a
- a) Correct: Complete linkage → genes always inherited together → 0% recombination.
Q89. Genetic maps are based on:
a) Crossing over frequency
b) Mutation frequency
c) Chromosome length
d) Nondisjunction events
Answer: a
- a) Correct: Genetic maps measure recombination frequency between genes.
Q90. 1% recombination is equivalent to:
a) 1 centimorgan
b) 1 chromosome
c) 1 gene
d) 1 karyotype
Answer: a
- a) Correct: 1% recombination = 1 centimorgan (cM) genetic distance.
Q91. Who prepared the first genetic map?
a) Morgan
b) Sturtevant
c) Bateson
d) Sutton
Answer: b
- b) Correct: Sturtevant, Morgan’s student, made the first genetic map in Drosophila.
Q92. Which of the following organisms was extensively used by Morgan for linkage studies?
a) Pea plant
b) Maize
c) Drosophila melanogaster
d) Mouse
Answer: c
- c) Correct: Drosophila was Morgan’s model organism.
Q93. If recombination frequency between two genes is 50%, then:
a) Genes are tightly linked
b) Genes are unlinked
c) Genes are on same chromosome
d) Genes show complete linkage
Answer: b
- b) Correct: 50% recombination = behaves as if on different chromosomes → unlinked.
Q94. In Drosophila, eye color and wing shape were studied by:
a) Bateson
b) Morgan
c) Punnett
d) Sutton
Answer: b
- b) Correct: Morgan studied eye color and wing shape linkage in Drosophila.
Q95. Crossing over is important because it:
a) Causes mutation
b) Increases genetic variation
c) Destroys linkage completely
d) None of these
Answer: b
- b) Correct: Main role = increases genetic variability in populations.
Q96. What is the physical basis of recombination?
a) Mutation
b) Chromosome replication
c) Crossing over
d) Independent assortment
Answer: c
- c) Correct: Recombination occurs due to crossing over.
Q97. What is meant by incomplete linkage?
a) No crossing over
b) Crossing over occurs between linked genes
c) Genes are always inherited together
d) Genes assort independently
Answer: b
- b) Correct: Incomplete linkage = linked genes can be separated by crossing over.
Q98. Linked genes are usually located:
a) On different chromosomes
b) Close to each other on the same chromosome
c) On the centromere
d) Randomly on all chromosomes
Answer: b
- b) Correct: Linked genes = closely located on same chromosome.
Q99. If two genes show 10% recombination, they are considered:
a) Tightly linked
b) Unlinked
c) Located on different chromosomes
d) Mutated
Answer: a
- a) Correct: 10% recombination = tight linkage.
Q100. What is the main difference between linkage and independent assortment?
a) Linked genes assort together, independent genes assort separately
b) Both are same
c) Linkage occurs in mitosis, assortment in meiosis
d) Linkage occurs only in prokaryotes
Answer: a
- a) Correct: Linked genes stay together; independent assortment occurs when genes are on different chromosomes.
Q101. Which stage of meiosis is most important for crossing over?
a) Pachytene
b) Diplotene
c) Zygotene
d) Diakinesis
Answer: a
- a) Correct: Crossing over occurs during pachytene stage of prophase I.
Q102. Chiasmata are first visible during:
a) Leptotene
b) Pachytene
c) Diplotene
d) Zygotene
Answer: c
- c) Correct: Chiasmata (cross-shaped structures) appear in diplotene.
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