Genetic Disorders

Genetic Disorders

• Caused by a harmful mutation (physical change of gene)

• Mutation originally occurs in gamete and is passed to future generations (inherited)

• The gene that is mutated determines the disease. The allele that is mutated determines its inheritance pattern

Autosomal Recessive• Mutation produces a recessive allele

• Genotypes:

CC: unaffected

Cc: carrier (unaffected)

cc: affected

• Examples: Cystic Fibrosis, Tay-Sachs, Sickle Cell Anemia (inc. dominance)

If two unaffected parents have a child with cystic fibrosis, what are their genotypes?

Autosomal Recessive Pedigree

X-linked Recessive• Mutation produces a recessive allele on the X chromosome.• Genotypes:

• Examples: Hemophilia A, Red-green Color Blindness

Female Male

XHXH - unaffected XHY - unaffected

XHXh – carrier (unaffected) XhY - affected

XhXh - affected No male carrier

Diane’s father and brother have hemophilia. There is no family history of hemophilia in Craig’s family. What is the probability that their child will have hemophilia. What if they have a girl? A boy?

X-linked Recessive Pedigree

Autosomal Dominant• Mutation produces a dominant allele

• Genotypes:

HH: affected

Hh: affected

hh: unaffected

• Examples: Huntington Disease

Although Huntington disease is very rare in the total population, it appears at a rate of 50 percent in affected families. Explain this in genetic terms.

Autosomal Dominant Pedigree

Chromosomal Disorders

• +/- chromosomes1 extra: trisomy1 missing: monosomy

• Caused by nondisjunction: failure of one or more chromosome pairs to separate during meiosis

• Examples: Down Syndrome, Klinefelter’s Syndrome, Turner’s Syndrome

Nondisjunction can occur during Meiosis I or Meiosis II

Down Syndrome (Trisomy 21)

Turner Syndrome (45, X)

Klinefelter Syndrome (47, XXY)