-in 90% of Trisomy 21 cases,the additional chromosome comes from the mothers egg rather than the fathers sperm.
-described in 1866,1959 French doctor named Jerome Lujeune discovered it was caused by the inheritance of an extra chromosome 21
-down syndrome occurs in about 1 in 800 live births.
Down Syndrome ." KidsHealth - the Web's most visited site about children's health. N.p., n.d. Web. 11 Mar. 2013. <http://kidshealth.org/parent/medical/genetic/down_syndrome.html>.
"Down Syndrome: MedlinePlus." National Library of Medicine - National Institutes of Health. N.p., n.d. Web. 11 Mar. 2013. <http://www.nlm.nih.gov/medlineplus/downsyndrome.html>.
"Down syndrome - PubMed Health."National Center for Biotechnology Information. N.p., n.d. Web. 11 Mar. 2013. <http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001992/>.