Question

What is linkage? Describe its types. Give four factors affecting Linkage.

Answer 1

The physical association of non-parental gene combinations is called linkage. The linked genes are located in the same chromosome. They do not independently assort but remain together in gametes and the offspring. In a dihybrid cross of the progeny, linked genes are 50 percent.

Following are the two types of linkage:

1. Complete linkage: When the genes are closely located in the chromosome and there is no chance of separating them by crossing over, then it is known as complete linkage. They are always transmitted together to the same gamete and offspring.
2. Incomplete linkage: When the genes are distantly located in the chromosome and there is a chance of separation by crossing over, then it is known as incomplete linkage. They transmit into different gamete and offspring.

Following are the factors affecting linkage:

1. Distance between the genes: As the distance between genes increases, chance of linkage decreases.
2. Age: With increase in age, chances of crossing over decreases which results in the increase of linkage.
3. Temperature: Rise in temperature causes the chances of chiasmata formation. It decreases the strength of linkage.
4. X-rays: Strength of linkage decreases if genes are exposed to X-rays.