Principles of Inheritance and Variation - Chromosomal Disorders

Chromosomal disorders are caused due to the absence, excess, or abnormal arrangement of one or more chromosomes.

Aneuploidy is the phenomenon of gain or loss of a chromosome(s) due to the failure of segregation of chromatids during cell division. Examples include $2n + 1$ (Trisomy) and $2n - 1$ (Monosomy).

Polyploidy is a condition where an increase in a whole set of chromosomes occurs in an organism, often seen in plants due to failure of cytokinesis after the telophase stage ($3n, 4n, etc.$).

Down's Syndrome is caused by the trisomy of chromosome $21$. The affected individual has a total of $47$ chromosomes.

Klinefelter's Syndrome is a sex-linked chromosomal disorder caused by the presence of an additional copy of the $X$ chromosome in males, resulting in a karyotype of $47, XXY$.

Turner's Syndrome is caused due to the absence of one of the $X$ chromosomes in females, resulting in a karyotype of $45, X0$.