Chromosome Mutations

• A large piece of a chromosome is altered during meiosis

• Addition of an extra chromosome

• Deletion of a chromosome

Down SyndromeBy: Mr. Morse

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

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

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.

Prevalence• Increased risk of down syndrome with age of

mother.

• Age 20 – 1/2000

• Age 35 – 1/350

• Age 40 – 1/100

• Age 45 – 1/35

• Due to increased chance of loss of spindle fiber checkpoint

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

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

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. 2015.

Mayo Clinic. "Down Syndrome." Definition. Mayo Foundation for Medical Education and Research, n.d. Web. 13 Jan. 2015.

NDSS. "Down Syndrome Facts." - National Down Syndrome Society. National Down Syndrome Society, n.d. Web. 11 Jan. 2015.

WebMD. "Down Syndrome Symptoms -- Typical Physical Characteristics." WebMD. WebMD, n.d. Web. 11 Jan. 2015.