Genetic Disorders

Within the dominant-recessive principle, individuals may be carriers for certain genetic disorders.
For recessive genetic disorders, in accordance with the Punnett square, two carrier parents must pass along recessive genes
Sex-linked genes: when a mutated gene is carried on the X chromosome, the result is called X-linked inheritance.
- Implications for males (XY) may be very different from those for females (XX).
Other genetic disorders may be due to chance or from damage from an environmental agent may produce a mutated gene, which is a permanently altered segment of DNA.

Chromosomal abnormalities typically occur because of errors in cell division (as opposed to inheritance)
The most common genetic disorder in children is Down syndrome.
- It is responsible for about 40 percent of cases of moderate-to- severe intellectual disability as defined by performance on an

intelligence test.

The condition is also called trisomy-21 because it is characterized in more than 90 percent of cases by an extra 21st chromosome.
A person with DS has distinct facial features, intellectual disability, and oftentimes heart and gastrointestinal disorders.
Generally seen as sociable, friendly, occasionally obstinate , though many individual and personality differences
Symptoms vary from person to person and can range from mod to severe.
With early intervention, the life expectancy of persons with Down syndrome has increased in recent years

Down syndrome: an extra chromosome causes mild to severe intellectual disability and physical abnormalities.
- Treatment for down syndrome: surgery, early intervention, infant stimulation, and special learning programs
- Incidence of down syndrome: 1 in 1,900 births at age 20. 1 in 300 births at age 35. 1 in 30 births at age 45.
Klinefelter syndrome (XXY): an extra X chromosome causes physical abnormalities.
- Treatment for klinefelter syndrome: hormone therapy can be effective
- Incidence of klinefelter syndrome: 1 in 1000 male births.
Fragile X syndrome: an abnormality in the X chromosome can cause intellectual disability, learning disabilities, or short attention span.
- Treatment for fragile X syndrome: special education, speech and language therapy
- Incidence of fragile X syndrome: more common in males than females
Turner syndrome (XO): a missing X chromosome in females can cause intellectual disability and sexual underdevelopment.
- Treatment for turner syndrome: Hormone therapy in childhood and puberty
- Incidence of turner syndrome: 1 in 2500 female births
XYY syndrome: an extra Y chromosome can cause above average height
- Treatment for XXY syndrome: no special treatment required
- Incidence of XYY syndrome: 1 in 1000 male births