Question

Differentiate between.
Single crossing over and double crossing over

Answer 1

Hint: The crossing over is the mutual exchange of the equivalent parts of the nearby paternal and the maternal chromatids that occurs in the pachytene stage of the meiosis 1. The obtained chromatids after the crossing over is called crossing over recombinants. The chromatids that are left from the crossing over are called the non-crossing over recombinants.

Complete answer:
The two chromosomes are aligned nearby to each other. And the particular segment of the chromosomes is alone interchanged and all the other areas of the chromosomes remain as such. This occurs in the two ways as single crossing over and the double crossing over.

Characteristics	Single crossing over	Double crossing over
Definition	The crossing occurs at the single point along the entire length of the chromosomes.	This double crossing over occurs at the two points in the same chromosomes.
Point of break and join	The chromosomes break and join at one point.	Here the breaking and the rejoining of the chromosomes takes place at two points.
Expectation of frequency	It is expected to be high frequency.	This type of crossing over has the low frequency of expectation.
Number of contact	The number of contact between the two chromosomes is one.	The number of contacts between the two chromosomes are two.

Note: The significance of the crossing over is to form the new organisms with the new combination in the traits. This is also helpful in establishing the genes in the linear arrangement. This is also useful in the mapping process of the chromosomes by locating the genes in the chromosomes.