Failure of segregation of chromatids during cell division results in the gain or loss of chromosomes. What is it called?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Aneuploidy
A normal human cell has 46 chromosomes. Errors in cell division can change this number in two ways. If the chromatids fail to separate, a cell gains or loses one or a few chromosomes. This is aneuploidy. If cytokinesis fails after telophase, a whole set of chromosomes is added. This is polyploidy.
Option (1) Polyploidy — Incorrect. Polyploidy is an increase by a whole set of chromosomes. It follows failure of cytokinesis, not failure of chromatid separation. It is common in plants.
Option (2) Euploidy — Incorrect. Euploidy means a cell has complete sets of chromosomes, such as the normal diploid state. No single chromosome is gained or lost.
Option (3) Aneuploidy — Correct. Failure of chromatid segregation leaves one chromosome extra or missing. Down’s syndrome (an extra chromosome 21) and Turner’s syndrome (one X missing) are examples.
NCERT Extract:
Chromosomal Disorders – “The chromosomal disorders on the other hand 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 example, Down’s syndrome results in the gain of extra copy of chromosome 21. Similarly, Turner’s syndrome 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.”