Tuesday, October 6, 2009

A Little Science Lesson

So we are on day 6 of "31 for 21" and I wanted to explain a little bit of the science behind Down syndrome. It takes me back to high school to write all this! But it was part of learning about who Aubrey is. Just so you know, we did not have any "testing" done before she was born. We knew we would love her no matter what and she was a blessing. We tried to have the genetics done when she was born, but the test got messed up and we have not had it done to see what type she has. I hope that this gives you knowledge and isn't borning:)

Our genetic material comes from mom and dad. We get 23 chromosomes from each one. They combine and produce a cell with 46 chromosomes which then divides, the result being that every cell contains identical genetic material.

Down syndrome is when a person has three copies of chromosome 21 instead of just two. That is why Down syndrome is often refered to as Trisomy 21. Every cell in a person with Ds will contain 47 chromosomes instead of 46, with one exception (Masaic, but I'll get to that). There are many theories about how the extra chromosome causes the effects of Down syndrome but little is currently known and there is nothing to prevent it or change your odds of having a child with Down syndrome. It occurs in all races and countires.

How it happen: During cell division to create either a sperm of egg, a cell containing 46 chromosomes divides into two cells each containing 23 chromosomes. Sometimes this division does not happen properly and one cell may contain 22 and the other 24. During fertilization, if the cell with 24 combines with a cell with 23 the result is 47 chromosomes. The trisomy can be on chromosome 21, resulting in Down syndrome. It can be on chromosome 13, resulting in Patau's syndrome or chromosome 18 and result in Edward's syndrome. Each has thier own characteristics and differences.

Three types:
Standard Trisomy 21 is when the extra chromosome 21 comes from either the egg or sperm cell. 90 to 95% of all Down syndrome are this type.
Translocation is caused when a piece of chromosome 21 is located on another chromosome such as 14. These people will have 46 chromosomes, but have the genetic material of 47 chromosomes. They will have all the characteristics of Trisomy 21 since they have three copies of chromosome 21. 3-5% are this type.
Mosaic is when a person has a mix of cells, some containing 46 chromosomes and some containing 47 chromosomes. This happens either when the person recieves 46 chromosomes at fertilization, but somewhere during early cell division the chromosome 21 cell pairs fail to split creating a cell with 47 chromosome and a cell with 45 chromosomes. The cell with 45 doesn't survive, but the one with 47 will continue to divide. So some cells in the person will contain 46 chromosomes or 47 chromosomes. The other way is that a person recieves 47 chromosomes at fertilization but later during cell division the extra chromosome is lost. Mosaic happens in 2-5% of cases. They may exhibit some, all, or none of the characteristics of Down syndrome depending on the percent of cells carrying the extra chromosome and where these cells are located.

All of this...to create our beautiful baby girl...Aubrey Elizabeth. There is just a little extra in her to love...that's all. And we certainly think that she is unique, just like everybody else.


  1. HI! I just found your blog because I read Bridgets light and saw your comment. I do not have a blog, but hope to start in the new year. I have four daughters too: 8,6,3 and 1 (so it was exicitng to see your family of four girls). Our youngest was born w/Down Syndrome on 8-17-2008. It has been quite a journey for me....I will be back to read your blog. I had to say hello....four girls are so wonderful, I am sure you agree :) Andrea Wiley, CA

  2. Hi Andrea, it certainly is a special thing to have 4 girls. We would love to hear about your youngest too. Our girls are 7,5,3,and 1. Thanks for stopping by.


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