AP BIOLOGY

Detailed explanation-1: -Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21. This extra genetic material causes the developmental changes and physical features of Down syndrome.

Detailed explanation-2: -Typically, a baby is born with 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. A medical term for having an extra copy of a chromosome is ‘trisomy.’ Down syndrome is also referred to as Trisomy 21.

Detailed explanation-3: -If a sperm with one copy of chromosome 21 fertilized the egg, then the child would end up with Down syndrome. But what if that egg happened to get fertilized by a sperm lacking a chromosome 21? Now the child would have the usual number of chromosomes but both copies would come from mom.

Detailed explanation-4: -Down syndrome occurs when there is an extra chromosome (full or partial) of the number 21 chromosome. Typically, a baby is born with 46 chromosomes, but with Down syndrome, the infant has an additional copy of the chromosome 21. This extra chromosome changes the way the baby’s body and brain develop.

Detailed explanation-5: -Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21) and results in a large number of phenotypes, including learning difficulties, cardiac defects, distinguishing facial features and leukaemia. These are likely to result from an increased dosage of one or more of the ∼310 genes present on Hsa21.