This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Linkage and Crossing Over – 1”.
1. The tendency of linkage is directly proportional to the rate of crossing over between two genes.
Explanation: If two genes are linked then they have a tendency of being transferred together, thus there will be a lesser tendency of crossing over between the genes. Thus the relation is inversely proportional not directly proportional.
2. Linkage ________ as the distance between two genes ______________
a) Decreases, decreases
b) Unaffected, Decreases
c) Decreases, Increases
d) Increases, Increases
Explanation: As the distance between the two gens increase, the probability of recombination event occurring between then is higher. Thus, linkage increases as the distance between two genes decrease and vice-versa.
3. In Drosophila males there is complete linkage. What is the reason behind this?
a) The genes are very closely located
b) Coupling theory
c) No synapsis
d) Unknown reason
Explanation: In Drosophila male these is no formation of synaptonemal complex, hence no synapsis is the pachytene phase of meiosis I. As there is no synapsis, there is no recombination.
4. Linkage results in __________
a) Formation of more Dominant phenotype
b) Formation of more Wild phenotype
c) Formation of more parental phenotype
d) Formation of more recombinant phenotype
Explanation: Linkage prevents recombination, thus it results in the formation of more parental phenotypes and lesser wild phenotypes. But it is not determining dominant/recessive traits or wild/mutant trait as that depends on genetic constitution of the parent.
5. If you suddenly observe linkage between two genes that are present in two chromosomes, this can be due to __________________
d) Non-homologous end joining
Explanation: Translocation of a gene from one chromosome to another within the same genome will result in then being on same chromosome. Then they can show linkage relationship.
6. Accurate mapping of genes can be done using _______
a) Two point mapping
b) Three point mapping
c) Single gene mapping
d) None of the mentioned
Explanation: When the distance between two genes is quite large there is increases possibility of double recombination event occurring between them. This can be avoided by 3 point mapping.
7. Recombination occurs in _________
a) Single strand stage
b) Two strand stage
c) Three strand stage
d) Four stand stage
Explanation: The only possibilities in this case are recombination in 2 strands and 4 strand stage. The study of recombinants show that recombination at 2 stand stage will produce effectively the same combination as in the absence of recombination. Thus it must be in the 4 strand stage.
8. Double crossovers can involve two, three or four strands at a time. What will be the resultant percentage of recombined genes to normal genes in between which recombination occurred, taking all three types in consideration?
Explanation: Taking all types of a double cross over in consideration only 50% of the resultant will show recombination between the genes which are located on two sides of these recombination events.
9. You cross a p+/v+ p+/v+ male drosophila to a p-/v- p-/v- and obtain the F1 hybrid. Now you cross the F1 male with double recessive female. What will be the recombination phenotype in F2?
a) p+/v+ p-/v- only
b) p+/v+ p-/v- and p-/v- p-/v-
c) p+/v+ p-/v- and p-/v- p-/v- also p+/v- p-/v- and p-/v- p-/v-
d) p+/v+ p-/v- and p-/v- p-/v- also p-/v+ p-/v- and p-/v- p-/v-
Explanation: In male drosophila recombination is absent thus there can’t be formation of p+/v- and p-/v+ gametes at all. This can however be formed in case we use female F1 for the test cross.
10. In animals cytological study of recombination was done by_______________
a) Barbara McClintok
Explanation: Barbara McClintok and Creigton observed crossing over in Plants while Stern showed cytological observation of the same in animals.
Sanfoundry Global Education & Learning Series – Cytogenetics.
To practice all areas of Cytogenetics, here is complete set of 1000+ Multiple Choice Questions and Answers.