What is Crossing Over?
Crossing Over is an event in the field of genetics that refers to the inter-change of genetic material from two chromosomes that align closely with each other. This simply means that the genetic makeup of one chromosome is exchanged with that of another chromosome. These chromosomes contain genes which are the units of heredity and contain genetic information that is passed on from generation to generation. When crossing over occurs, a particular population will have increased genetic diversity across different generations. It is said that variations in the genetic composition is vital for the human species especially in the fight against several illnesses that affect certain groups of people.

The process of crossing over occurs at the time of DNA replication. And in the case of human beings, replication of DNA may come from two processes. Mitosis is a process that involves cell replication resulting to two copies of the original cell. Another process that involves replication is called meiosis. In this process, a female egg cell and a male sperm cell need to combine to form the fertilized egg. After several days, this particular egg will develop into an embryo which contains the chromosomal pairs. And when two chromosomes will align and pair up with each other closely, crossing over of DNA and/or genes may occur. Based on studies, the process of crossing over is much more frequent in meiosis than the process of mitosis. It is also said that crossing over is more common with females than in males during meiosis.

What makes the chromosomes exchange genetic material with each other are enzymes that unwound or uncoil them from their typical coiled state. It is typical of chromosomes to assume a compact and coiled formation but when these chromosomes are unwound, they have greater tendency to undergo “crossing over” with another chromosome nearby.