BOTANY Higher Secondary Second Year - Textbooks Online

When two genes are nearer, the probability of occurrence of crossing
over between them is limited.
Let A, B, C, D and E be five knots on a string separated by the distances
as shown. The probability of making a random cut between two knots is
directly proportional to the distance between them. Every cut separates A
from E, whereas 5/100th cut only separates C from D.If the knots or genes
linearly arranged on a chromosome in randoms are the cross overs, then C
and D remain linked, whereas A and E will not show linkage in this situation.
Uses of gene mapping
It is useful to determine the location, arrangement and linkage of
genes in a chromosome.
It is useful to predict the results of dihybrid and trihybrid crosses.
Self evaluation
I . Choose and write the correct options.
1. The coupling test cross ratio is
a. 1:7:7:1 b. 7:1:1:7
c. 1:1:1:1 d. 9:3:3:1
II. Answer the following questions in two or three sentences.
2. What is linkage?
3. What is coupling?
4. What is repulsion?
5. What is crossing over?
6. What is a genetic map?
7. What are the uses of gene mapping?
III. Answer the following questions in about 100 words.
8. Write short notes on crossing over.
9. What is crossing over? Write the significance of crossing over.
10. Write short notes on gene mapping.
11. Explain the coupling aspect in Lathyrus odoratus.
12. Explain the replusive aspect in Lathyrus odoratus.
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