Down syndrome & Trisomy 21

Da Kyung Lee

Science 9S

10/10/2014

Mr. Youell

Down Syndrome & Trisomy 21

Noah's birth story: how down syndrome changed our lives... for the better

(Figure 1: picture of Noah’s family)

Noah was born on December 15, 2010 with the parents’ love, happiness, joyfulness, and excitement. After the mother gave a birth to him, they were informed by the doctors and nurses that Noah has down syndrome. In previous, they were seriously in shock and felt like the time had just frozen. The mother cried out most but she didn’t ask for the family to be excused before giving us the Down syndrome diagnosis. Later, they calmed down and started to think positively with smile. Because it was a birth, not a funeral, thus, there was no reason to be depressed. Such as Noah, people with down syndrome are increasing and integrated into society and community organization with other people.

While I was creating the karyotype with the chromosomes that are mixed together, I realized that there is one more copy of a chromosome. This means that unlike normal people that have 46 chromosome in total in each cell, the individual has a trisomy disorder meaning he has 47 chromosomes in a cell. This person in particular has an extra 21st chromosome so he has a disorder called trisomy 21 also known as down syndrome.

(Figure 2:karyotype of a human who has down syndrome)

(Figure 3: karyotype of a normal human)

Down syndrome occurs when an individual cell has a full or incomplete extra copy of chromosome 21. People who have down syndrome have some physical characteristics such  as low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm. In America, about 6,000 babies with down syndrome are born each year caused by the most common genetic condition in USA. An accurate description of a person with down syndrome was published by John Langdon Down in 1866. Although other people had recognized the characteristics of down syndrome before, Down was first who described the condition as noticeable and distinct entity. There are three different types of down syndrome such as trisomy 21 (nondisjunction), translocation and mosaicism. According to the site naming healthline, nondisjunction is called when an error is happened in cell division and this is usually caused of down syndrome. This is the most common form of down syndrome. Next for translocation, children have only one extra part of chromosome 21. There are total 46 chromosome, however, one of them has an extra piece of chromosome 21 attached. Lastly, mosaicism means there is an extra chromosome in some but not all of a child's cells.

(Figure 4: typical cell division) 

(Figure 5: nondisjunction cell division)

Down syndrome is usually happened to the children in certain parents. There are specially four ways that down syndrome possibly happens to the babies. First, when a mother's age is 35 or older than 35. Second, when a father's age is 50 or older than 50. Third, when people of a family have a history of down syndrome. Fourth, when there are people who carry the genetic translocation. 

Sources:

• http://www.ndss.org/Down-Syndrome/What-Is-Down-Syndrome
• http://noahsdad.com/story
• http://www.healthline.com/health/down-syndrome#Causes2