How do chromosomes gain an extra copy of a gene during meiosis

              Non dis junction

Explanation:

                      Non dis junction is the phenomena in which the chromosomes fails to separate during the meiosis and the chromosome get an extra copy of the chromosome. The condition is mainly related to the age of the female individual and results in the production of gametes with extra set of genes or duplicated gene. In example we can study about the enupliody, XXXsyndrome, Down syndrome. This is an abnormal condition which leads to the production of an abnormal individual which have the symptoms not related to normal individual