Define aneuploidy. How is it different from polyploidy ? Describe the individuals having the following chromosomal abnormalities. (a) Trisomy of `21^(st)` chromosome (b) XXY (c) XO

Explanation

Definition of Aneuploidy : Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s) called aneuploidy.

=(1) Down.s Syndrome (Mongolism) : This is a autosomal aneuploidy It is causeddue to presence of an additional copy of the chromosome number 21 (trisomy of 21) due to non-disjunction of chromosomes during sperm or ova formation. 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.
= (ii) Klinefelter.s Syndrome : This genetic disorder is trisomy of sex chromosomes is also caused due to the presence of an additional copy of X-chromosome. They have 47 chromosomes., They have karyotype of XXY. Such an individual has overall masculine development, however, the feminine development (development of breast, i.e., Gynaecomastia) is also expressed. Such individuals are sterile male.
= (iii) Turner.s Syndrome : Such females are sterile as ovaries are rudimentary besides other features including lack of other secondary sexual characters. This is a monosomy of sex chromosome,Such a disorder is caused due to the absence of one of the X chromosome, They have 45 chromosomes. They can be represented as XO.