Linkage and Crossing Over MCQs

In eukaryotes, genetic linkage and crossing over are two distinct processes that are intimately related to one another. The process by which genetic material in the germline is transferred from one individual to another is referred to as crossing over. The tendency of genes to remain close to one another in a chromosome is known as genetic linkage. Linkage is the process by which genes are kept within a chromosome so that they can be inherited together. The process of crossing over allows for the separation of genes on a chromosome and also divides the chromosome into its component gametes.

1. Crossing over occurs in the

1. 1.  Diakinesis stage
   2. Anaphase stage
   3.  Pachytene stage
   4.  Leptotene stage

The answer is: (C)

2. A Drosophila has four pairs of chromosomes. It contains the following connection groups:

1. 1. one more than the pair of chromosomes
   2.  one less than the pair of chromosomes
   3.  four
   4. eight

The answer is: (C)

3. The percentage of people that cross over is higher when

1. 1. The genes are in a distinct cell.
   2.  There is no relationship between genes.
   3.  connected genes are near to one another.
   4. related genes are separated by a large distance.

The answer is: (D)

4. If a proportion of two genes crosses over, the distance between them is 10.

1. 1. 5 morganoid
   2. 10 centimorgans
   3. 20 centimorgans
   4. 40 map units

The answer is: (B)

5. A phenomenon known as chromosomal separation can occasionally separate alleles of different genes on the same chromosome.

1. 1. crossing over
   2. continuous variation
   3. epistasis
   4. pleiotropy

The answer is: (A)

6. Repulsion and coupling are two sides of the same coin.

1. 1. mutation
   2. chiasmata
   3. linkage
   4. crossing over

The answer is: (C)

7. If the gene frequency between genes a and c is 2%, b and c is 13%, b and d is 4%, a and b is 15%, c and d is 17%, and a and d is 19%. A chromosome’s gene sequence is called

1. 1. a,d,b,c
   2. d,b,a,c
   3. a,b,c,d
   4. a,c,b,d

The answer is: (D)

8. This is why Mendel failed to notice the linking phenomena in his experiments.

1. 1. He solely researched pure plants.
   2. He lacked a strong microscope.
   3.  the characters he looked at were on different chromosomes
   4. a large number of chromosomes to manage

The answer is: (C)

9. In a linear chromosome map, the distance between four loci is as follows: a-b is 10%, a-d is 3%, b-c is 4%, and a-c is 6%. The frequency of crossover between c and d is

1. 1. 4-12%
   2. 3-6%
   3. 9%
   4. 3%

The answer is: (D)

10. Where did you get this evidence? — chromosomal crossover occurs at the four-stranded stage rather than the two-stranded stage.

1. 1. research on Drosophila chromosomal linkage maps
   2. research on maize meiosis
   3. Ascospores of Neurospora are organised in a 4:4 ratio.
   4. Ascospore arrangement in Neurospora 2:2:2:2.

The answer is: (D)

11. There is a crossing across between Non-sister chromatids of a non-homologous chromosome at the zygotene stage of prophase I.

1. 1. At the pachytene stage of prophase I, non-sister chromatids of a homologous chromosome
   2. At the pachytene stage of prophase I, non-sister chromatids of non-homologous chromosomes.
   3.  At the zygotene stage of prophase I, non-sister chromatids of a homologous chromosome

12. The rate of crossing over between two genes is directly proportional to the propensity of linkage.

1. 1. Yes
   2.  Untrue

Answer: B Explanation: When two genes are connected, they are more likely to be transferred together, reducing the likelihood of cross-over between them. As a result, rather than being exactly proportionate, the relationship is inversely proportional.

13. Linkage is defined as the distance between two genes

1. 1. Decreases, decreases, decreases, decreases, decreases, decreases, decreases,
   2. Has no effect, but decreases
   3. Decreases and Gains
   4. Increases, Increases, Increases, Increases, Increases, Increases, Increases, Increases

C is the answer

Explanation: As the distance between two genes grows, the likelihood of a recombination event between them grows. As the distance between two genes decreases, linkage increases, and vice versa.

14. There is full linkage in Drosophila males. What exactly is the rationale for this?

1. 1. The genes are close together.
   2. Theory of coupling
   3. There is no synapsis
   4. Unidentified cause

Answer: C Explanation: Because no synaptonemal complex forms in male Drosophila, there is no synapsis during the pachytene phase of meiosis I. There is no recombination since there is no synapsis.

15. The effect of linking is .

1. 1. The development of more dominant phenotypes
   2. The development of more wild phenotypes
   3.  The development of more parental phenotypes
   4. More recombinant phenotype formation

Answer: C Explanation: Because linkage hinders recombination, more parental phenotypes and fewer wild phenotypes are formed. It does not, however, determine dominant/recessive features or wild/mutant traits, as these are determined by the parent’s genetic constitution.

16. ______ can be used to map genes accurately.

1. 1. Mapping of two points
   2. Mapping in three dimensions
   3. Mapping of a single gene
   4.  None of the preceding

Explanation: When the distance between two genes is relatively high, the likelihood of a double recombination event between them increases. Three-point mapping can help you prevent this.

17. Recombination happens in

1. 1. Stage of a single strand
   2. Stage with two strands
   3. Stage of three strands
   4. Stage with four stands

Answer: D Explanation: In this scenario, the only options are recombination in two strands and recombination in four strands. The analysis of recombinants revealed that recombination at the two-stand stage produces the same combination as if no recombination took place. As a result, it must be in the fourth strand stage.

18. Two, three, or four strands can be crossed at the same time in a double crossover. Taking into account all three types of recombination, what will be the consequent percentage of recombined genes to normal genes between which recombination occurred?

1. 1.  0%; b) 0%; c) 0%;
   2. fifty percent
   3. 70 percent
   4. 90 percent 

Answer: B Explanation: When all sorts of double crosses are considered, only 50% of the resulting will demonstrate recombination across the genes on opposite sides of the recombination events.

19. In animals cytological study of recombination was done by______________

1. 1. Barbara McClintok
   2.  Stern
   3. Creigton
   4. Mandel

Answer: B Explanation: Barbara McClintok and Creigton observed crossing over in plants, while Stern demonstrated the same in mammals using cytology.