Question

Down's syndrome occurs as a result of :

• A. Tetrasomy
• B. Trisomy
• C. Autopolyploidy
• D. Allopolyploidy

Answer 1

The correct option is B Trisomy

• Trisomy : Trisomy is a type of aneuploidy (an abnormal number of chromosome) in which instead of two chromosome there is an extra copy of a particular chromosome. Down's syndrome occurs as a result of an extra number of chromosome 21, which is a condition called Trisomy.
• Tetrasomy : A tetrasomy is a form of aneuploidy with the presence of extra two copies of chromosome, instead of the normal two, of a particular chromosome.
• Autopolyploidy : Autopolyploidy occurs when an individual has more than two sets of chromosomes, both of which from the same parental species.
• Allopolyploidy : Allopolyloidy occurs when the individual has more than two copies which comes from different species.

Therefore, option b) is the correct answer.