GENERAL HISTOLOGY

Detailed explanation-1: -Down syndrome is usually caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.

Detailed explanation-2: -Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21.

Detailed explanation-3: -The overwhelming majority of trisomy 21, or Down syndrome, is caused by the failure of chromosomes to separate properly during meiosis, also known as chromosome nondisjunction.

Detailed explanation-4: -Conditions that arise from non-disjunction events include: Patau’s Syndrome (trisomy 13) Edwards Syndrome (trisomy 18) Down Syndrome (trisomy 21)

Detailed explanation-5: -The older the mother, the higher than chances of producing a child with Down syndrome. Nondisjunction during sperm production can lead to sperm gametes with abnormal numbers of chromosomes. Trisomy 21 is always the result of nondisjunction that occurs during meiosis I.