PATHOLOGY

Detailed explanation-1: -Trisomy 21 (also known by the karyotype 47, XX, +21 for females and 47, XY, +21 for males. According to the gene-dosage effect hypothesis, the genes located on chromosome 21 have been overexpressed in cells and tissues of Down syndrome patients, and this contributes to the phenotypic abnormalities.

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: -Trisomy 21. An estimated 95% of people with Down syndrome have trisomy 21, meaning they have three number 21 chromosomes instead of two. A person normally has 23 pairs of chromosomes, each made up of genes.

Detailed explanation-4: -Chromosome 21 likely contains 200 to 300 genes that provide instructions for making proteins.

Detailed explanation-5: -Trisomy 21 may be diagnosed through direct analysis of fetal chromosomes, by karyotype or DNA microarray, obtained from amniocentesis, chorionic villus sampling, or percutaneous umbilical blood sampling.