AP BIOLOGY

Detailed explanation-1: -A medical term for having an extra copy of a chromosome is ‘trisomy.’ Down syndrome is also referred to as Trisomy 21. This extra copy changes how the baby’s body and brain develop, which can cause both mental and physical challenges for the baby.

Detailed explanation-2: -The classic form is the most common chromosomal disorder, in which there is one extra X chromosome resulting in the karyotype of 47, XXY [18]. Double aneuploidy was first described in a patient with both Down and Klinefelter (48, XXY, +21) syndromes.

Detailed explanation-3: -Also known as Down syndrome, trisomy 21 is a genetic condition caused by an extra chromosome. Most babies inherit 23 chromosomes from each parent, for a total of 46 chromosomes. Babies with Down syndrome however, end up with three chromosomes at position 21, instead of the usual pair.

Detailed explanation-4: -Double aneuploidy (Down-Klinefelter syndrome) is rare, with an estimated incidence of 0.4-0.9 cases per 10, 000 male births and 11.7 cases per 10, 000 cases of trisomy 21 [7]. It is characterized by the presence of a third copy of chromosome 21 plus an extra X chromosome, resulting in 48 chromosomes (48, XXY, +21).