Question

Down syndrome results from nondisjunction of which chromosome?

1) Y
2) X
3) 21
4) 12

Answer 1

Down syndrome is caused by the nondisjunction of chromosome 21 during meiosis, leading to an extra copy of this chromosome, known as Trisomy 21.

Step-by-step explanation:

Down syndrome, also known as Trisomy 21, is a genetic disorder caused by the nondisjunction of chromosome 21 during meiosis. Nondisjunction is an error in which chromosomes do not separate properly, leading to gametes (sperm or egg cells) with an abnormal number of chromosomes. If a gamete with an extra copy of chromosome 21 is fertilized by a normal gamete, the resulting zygote will have three copies of chromosome 21 instead of the usual two, which leads to Down syndrome. This can happen due to issues with the spindle checkpoint, which monitors proper chromosome segregation during cell division.

Down syndrome is characterized by physical growth delays, characteristic facial features, and mild to moderate intellectual disability. It is a condition that affects individuals from infancy into adulthood. The chance of having a child with Down syndrome increases with maternal age, especially in women over the age of 36.