Match Column 1 with Column 2 :

A-iv, B-i, C-ii, D-iii

The correct answer is option (2) -A-iv, B-i, C-ii, D-iii

A. Down’s Syndrome : The cause of this genetic disorder is the presence of an additional copy of the chromosome number 21 (trisomy of 21). This disorder was first described by Langdon Down (1866). The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.

B. Crossing over occurs between non-sister chromatids of homologous chromosomes, leading to the exchange of genetic material.

C. X and Y are the sex chromosomes in humans that determine an individual's sex. Sex determination in human embryos is based on the combination of sex chromosomes inherited from the parents. Humans have two types of sex chromosomes, X and Y:

• Females have two X chromosomes (XX).
• Males have one X and one Y chromosome (XY).

D. 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.