More Genetic Disorders

Objectives

• Explain what it means to be a carrier
• Provide examples and describe genetic disorders

Genetic disorders may be caused by mutations or an abnormal number of chromosomes.

Achondroplasia

• Most common form of dwarfism
• Caused by a dominate mutation
• Can be passed to offspring

Disorders caused by mutations

• Marfan syndrome (dominant)
• Sickle cell anemia (recessive)
• Vitamin D resistant rickets (dominant)
• Hemophilia A (recessive)

People who inherit just one copy of a recessive allele do not express it. They are called carriers.

Chromosomal Disorders

Nondisjunction is the failure of replicated chromosomes to separate during meiosis. Some resulting gametes will have an extra chromosome, others will be missing one.

Example: Down syndrome
Individual has an extra copy of chromosome 21

Many chromosomal disorders involve the X chromosome.

Examples

• Turner's syndrome (XO)
• Triple X syndrome (XXX)
• Kleinfelter's syndrome (XXY)