a. Trisomy of 21st Chromosome

b. XXY

c. XO

Solution:

Aneuploidy occurs when chromatid segregation fails during the cell division cycle, resulting in the gain or loss of a chromosome(s).

Polyploidy occurs when cytokinesis fails during the telophase stage of cell division, resulting in an increase in the total number of chromosomes in an organism.

a. Trisomy of 21st Chromosome

The genetic disorder of the presence of an additional copy of chromosome number 21 is called Down’s syndrome.

b. XXY

Klinefelter’s syndrome is a hereditary condition characterised by the presence of an extra copy of the X chromosome, resulting in a karyotype of 47, XXY.

c. XO

The disorder caused due to the absence of one of the X chromosomes, that is 45 with XO is called Turner’s syndrome.