BIOL 210 Module 7: Genetic Linkage, Recombination, and Mapping Updated and Latest Questions and Correct Answers with Rationale

BIOL 210 Module 7: Genetic Linkage,
Recombination, and Mapping Updated and Latest
Questions and Correct Answers with Rationale
1. Which phenomenon describes the tendency of DNA sequences that are close together on a
chromosome to be inherited together during meiosis?
A. Epistasis

B. Genetic Linkage

C. Independent Assortment

D. Codominance

Correct Answer: B
Explanation: Genetic linkage occurs when genes are located close to each other on the
same chromosome, making them less likely to be separated during crossing over.

2. What is the unit of distance used in genetic maps to represent a 1% recombination
frequency?
A. Nanometer

B. Kilobase

C. Centimorgan (cM)

D. Angstrom
Correct Answer: C
Explanation: One centimorgan (cM) or map unit (m.u.) is defined as the distance between
genes for which one product of meiosis out of one hundred is recombinant.

3. During which phase of meiosis does crossing over occur?
A. Prophase I

B. Anaphase II

C. Metaphase I

D. Telophase I

Correct Answer: A
Explanation: Crossing over, the exchange of genetic material between non-sister
chromatids of homologous chromosomes, occurs during Prophase I.

,4. In a testcross between a dihybrid (AaBb) and a homozygous recessive (aabb), 800 offspring
are produced. 400 are AaBb, 400 are aabb. What does this indicate?
A. The genes are 50 cM apart

B. The genes are on different chromosomes

C. The genes are perfectly linked with no crossing over

D. The genes show 100% recombination
Correct Answer: C
Explanation: Since only parental phenotypes (AaBb and aabb) were produced and no
recombinants (Aabb or aaBb) were seen, the genes are completely linked.

5. What is the maximum possible recombination frequency between two genes?
A. 50%

B. 25%

C. 75%

D. 100%

Correct Answer: A
Explanation: A recombination frequency of 50% is the maximum, representing
independent assortment where genes are either on different chromosomes or very far
apart on the same one.

6. If two genes show a recombination frequency of 15%, how many map units apart are they?
A. 7.5 m.u.

B. 15 m.u.
C. 30 m.u.

D. 1.5 m.u.
Correct Answer: B
Explanation: By definition, 1% recombination frequency equals 1 map unit (m.u.).
Therefore, 15% equals 15 m.u.

7. In a mapping experiment, the distance between Gene A and Gene B is 10 cM, and between
B and C is 15 cM. If the order is A-B-C, what is the expected distance between A and C?
A. 5 cM

B. 25 cM

C. 10 cM

, D. 150 cM

Correct Answer: B
Explanation: For linear maps, the distance between distal genes is the sum of the
intervening distances: 10 cM + 15 cM = 25 cM.

8. Which of the following increases genetic diversity by creating new combinations of alleles
on a single chromosome?
A. Crossing over

B. DNA Replication

C. Nondisjunction

D. Mitosis

Correct Answer: A
Explanation: Crossing over shuffles alleles between homologous chromosomes, creating
recombinant chromosomes that differ from the parental ones.

9. Which offspring classes are always the least frequent in a three-point testcross?
A. Parental types

B. Double crossovers

C. Single crossovers between the last two genes

D. Single crossovers between the first two genes
Correct Answer: B
Explanation: Double crossovers require two independent recombination events to occur
simultaneously, which is statistically less likely than a single event.

10. If a testcross results in 45% AB, 45% ab, 5% Ab, and 5% aB, what is the recombination
frequency?
A. 10%

B. 90%

C. 45%

D. 5%

Correct Answer: A
Explanation: The recombination frequency is the sum of the recombinant classes: 5% (Ab)
+ 5% (aB) = 10%.