Question

Describe chromosomal aberration with examples.

Hint:

Split into structural (deletion, duplication, inversion, translocation) and numerical (aneuploidy, polyploidy) aberrations, with Down syndrome as the classic example.

Answer 1

Understanding the Question:
A chromosomal aberration is a change in the normal structure or number of chromosomes, which can alter the phenotype of the affected individual.

Detailed Explanation:
Structural aberrations change the arrangement within a chromosome without necessarily changing chromosome number: deletion removes a chromosome segment, duplication repeats a segment, inversion reverses the order of a segment, and translocation moves a segment to a non-homologous chromosome.
Numerical aberrations change the total chromosome count. Aneuploidy is the gain or loss of one or a few chromosomes due to faulty separation (non-disjunction) during meiosis, and Down syndrome, caused by an extra copy of chromosome 21 (trisomy 21), is a well known human example.
Polyploidy is the gain of one or more complete extra sets of chromosomes, which is common in plants and often produces larger, more vigorous individuals, as seen in many cultivated wheat and cotton varieties.
Another human example of aneuploidy is Klinefelter's syndrome, where an individual has an extra X chromosome (genotype XXY), leading to male sterility.

Final Answer:
Chromosomal aberrations are structural changes (deletion, duplication, inversion, translocation) or numerical changes (aneuploidy such as Down syndrome, polyploidy in plants), both of which alter gene dosage or arrangement and can change the phenotype.