1. Chromosome Mutations
A large piece of a chromosome is altered during meiosis
Addition of an extra chromosome
Deletion of a chromosome

2. Down Syndrome
By: Mr. Morse

3. What is it?
Trisomy 21: Individuals with Down Syndrome have 3 copies of the 21st chromosome
Causes intellectual disabilities, health issues, and certain physical characteristics
Severity of Down Syndrome can vary greatly between individuals

4. Symptoms and Characteristics
Down Syndrome causes developmental delays and intellectual disabilities.
Characteristics of individuals with this syndrome include…
Low muscle tone
Flat facial features including a small nose
Small, abnormally shaped ears
Hyperflexibility
Single deep crease across the palm
About 50% of individuals with Down Syndrome have heart issues

5. Causes
Trisomy 21: Individuals with Down Syndrome have 3 copies of the 21st chromosome. (nondisjunction)
From improper division in meiosis I or meiosis II. One gamete will end up with 2 copies of the 21st chromosome.
Mosaic Down Syndrome: some cells have 3 copies, some have the normal 2
At some point development (after fertilization), during mitosis, some cells will end up an extra copy of the 21st chromosome
Translocation: individuals have normal number of chromosomes, but an extra section of a 21st chromosome is attached improperly to another chromosome.

6. Prevalence Increased risk of down syndrome with age of mother.
Due to increased chance of loss of spindle fiber checkpoint

7. Treatment There is no cure, it is a lifelong syndrome.
Individuals with Down Syndrome have a higher quality of life if early intervention is in place. This includes…
Speech therapy
Social skill development
Special education
Medical care
Life Expectancy:
60 years of age

8. Interesting Facts 90% of the cases are caused by trisomy in the egg.
4% from trisomy in the sperm
Many individuals with Down Syndrome grow up and hold jobs, participate in recreation, and even live independently

9. Works Cited
Bernasconi, Andrea. "Nondisjunction - The Causes Of Nondisjunction And Its Frequency In Humans." - Age, Chromosome, Spindle, and Cell. N.p., n.d. Web. 13 Jan
Mayo Clinic. "Down Syndrome." Definition. Mayo Foundation for Medical Education and Research, n.d. Web. 13 Jan
NDSS. "Down Syndrome Facts." - National Down Syndrome Society. National Down Syndrome Society, n.d. Web. 11 Jan
WebMD. "Down Syndrome Symptoms -- Typical Physical Characteristics." WebMD. WebMD, n.d. Web. 11 Jan