What are two major causes responsible for Down syndrome?

Answer 1

Down syndrome is the most common genetic cause of ID (intellectual disability). Down syndrome is caused by trisomy for chromosome specifically, duplication of 21q22.

• 95% of cases result from nondisjunction and resultant standard trisomy 21.
• The remaining 5% are relatively evenly split between robertsonian translocation, of which 14;21 translocation is most common and about half are familial.

note :

robertsonian translocation is a common form of chromosomal rearrangement that in humans occurs in the five acrocentric chromosome pairs, namely 13, 14, 15, 21, and 22.

Answer 2

down syndrome is the most common genetic cause of ID (intellectual disability). Down syndrome is caused by trisomy for chromosome specifically, duplication of 21q22.

• 95% of cases result from nondisjunction and resultant standard trisomy 21.
• The remaining 5% are relatively evenly split between robertsonian translocation, of which 14;21 translocation is most common and about half are familial.

note :

robertsonian translocation is a common form of chromosomal rearrangement that in humans occurs in the five acrocentric chromosome pairs, namely 13, 14, 15, 21, and 22.

Answer 3

There is only one and that is an extra chromosome.