Home | | Botany 12th Std | Genetic / linkage maps

## Chapter: 12th Botany : Practicals

Aim: To understand the frequency of recombination between the gene pairs on the same chromosome.

## Exercise : Genetic / linkage maps

### Aim:

To understand the frequency of recombination between the gene pairs on the same chromosome.

### Principle:

To analyse the relative distance between the various genes and map their position in the chromosome, which is called genetic or linkage maps.

### Requirements:

Different kinds of linkage / genetic maps can be constructed by giving the students the relative distance between the linked genes of a chromosome. A diagrammatic representation can be drawn showing the location and arrangement of genes and their relative distance between them.

## Solve the Problem

Problem: There are three linked genes A, B and C in a chromosome. Percentage of crossing over (recombination frequency) between A and B is 20, B and C is 28 and A and C is 8. What is the sequence of genes on the linkage map?

Given: Percentage of crossing over between the 3 linked genes A â€“ B = 20%, B â€“ C = 28% and A â€“ C = 8%.

### Solution ### Reasons:

Â·        The frequency of crossing over is directly proportional to the relative distance of the genes on the chromosomes.

Â·        More crossing over = More distance between two genes and Less crossing over = Less distance between the two genes.

In the above problem, the sequence of the genes on the linkage map is B, A, C

NOTE: Teachers can give different crossing over percentage between its linked genes in a chromosome and make the students construct the linkage maps. The external examiner can also do the same for the Board Practical Examinations.

Tags : Solving the Problems | Botany Practicals , 12th Botany : Practicals
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12th Botany : Practicals : Genetic / linkage maps | Solving the Problems | Botany Practicals