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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 person’s DNA– May occur during meiosis or may also
have been already present in the parent’s cells
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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 person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.
Cystic Fibrosis
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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 person’s 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?