Answer:
deletion of a chromosome.
Step-by-step explanation:
Changes usually occur in the nuclear material (chromosomes) of a cell. These changes are called MUTATION. A mutation, depending on how it occurs, consists of different types. Mutation can result into deletion of a chromosome or addition of a chromosome.
Deletion mutation is the removal of a part of the chromosome segment or chromosome while Insertion mutation is the addition of a part of the chromosome segment to the original chromosome. Both insertion and deletion can be detrimental to the organism as it can lead to the serious genetic disorders, however, deletion of a chromosome has the most adverse effect.
During deletion mutation, information encoded in a particular chromosome is lost completely which can make the resulting individual deficient of certain traits that makes him/her normal but in Insertion mutation, a different chromosome is added which can sometimes be beneficial to the resulting organism e.g can confer resistance to certain unfavorable condition.