Human Genetic Disorders

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Human Genetic Disorders
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Genetic Disorder

• An abnormal condition that a person inherits
  through genes or chromosomes.
• Caused by mutations, or changes in a persons DNA
• May occur during meiosis or may also have been
  already present in the parents cells

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Cystic Fibrosis
Chromosome 7
CFTR gene
The most common allele that causes cystic
fibrosis is missing 3 DNA bases. As a result,
the amino acid phenylalanine is missing from the
CFTR protein.
Normal CFTR is a chloride ion channel in cell
membranes. Abnormal CFTR cannot be transported
to the cell membrane.
The cells in the persons airways are unable to
transport chloride ions. As a result, the airways
become clogged with a thick mucus.
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Cystic Fibrosis Prognosis

• Not sex-linked
• No cure
• Drugs to prevent infection
• Physical therapy to break up mucus in lungs

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Sickle-Cell Anemia

• Genetic disorder that causes the production of
  abnormal hemoglobin.
• Hemoglobin is a protein in RBCs that carriers
  oxygen.
• Sickle-shape often blocks blood vessels resulting
  in lack of oxygen.

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Genetics Behind Sickle-Cell

• 9 of African Americans carry the sickle-cell
  allele
• Sickle-cell allele is codominant with normal
  allele
• Leads to resistance to malaria
• 2 Sickle-cell alleles results in sickle-cell
  symptoms

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Hemophilia

• Genetic disorder in which a persons blood clots
  very slowly or not at all.
• Individuals can bleed to death from a minor cut
  or scrape.
• Caused by recessive allele on the X chromosome.
• Treatment
• Receive doses of missing clotting protein
• Can lead relatively normal lives

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Down Syndrome

• Every cell has an extra copy of chromosome 21.
• Result of error during meiosis
• Distinctive physical appearance and some degree
  of mental retardation
• Many lead full, active lives.

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Tools in Diagnosing Genetic Disorders

• Amniocentesis
• Very long needle used to remove small amount of
  fluid that surrounds the baby
• Fluid contains cells from the baby
• Karyotype
• Picture of all the chromosomes in a cell
• Can reveal whether a developing baby has the
  correct number of chromosomes in its cells and
  whether it is a boy or girl.

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Genetic Counseling

• Helps couples understand their changes of having
  a child with a particular genetic disorder.
• Uses karyotypes, pedigree charts, and Punnett
  squares to determine if parents are carriers,
  etc.

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Summary Questions

• Explain how genetic disorders occur in humans.
  Give two examples of genetic disorders.
• Describe two tools that doctors use to detect
  genetic disorders.
• How do the cells of people with Down syndrome
  differ from those of others? How might this
  difference arise?

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Summary Questions

• A couple with a family history of hemophilia is
  about to have a baby girl.
• What information about the parents would you want
  to know?
• How would this information help you determine
  whether the baby will have hemophilia?