Question

How do chromosomal abnormalities due to change in the number of chromosomes arise? Give three examples of the occurrence of such abnormalities in humans.

Answer 1

The chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s), called aneuploidy.

For eg 1) Down's syndrome - It results in the gain of an extra copy of chromosome 21.

2) Turner's syndrome - It results due to loss of an X chromosome in human females.

Failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism and this phenomenon is known as polyploidy. This condition is often seen in plants.