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Biology_Study_Sheet - Prep101 http/www.prep101.com/mcat...

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© Prep101 http://www.prep101.com/mcat/ Page 1 of 9 DISORDERS AND DISEASES COMMONLY COVERED ON THE MCAT GENETIC DISORDERS ........................................................................................................... 1 NUTRITIONAL DISORDERS ................................................................................................ 4 INFECTIOUS DISEASES ......................................................................................................... 5 OTHER COMMON DISEASES .............................................................................................. 6 GENETIC DISORDERS Single-Gene Disorders This category encompasses a wide variety of diseases and disorders, ranging in frequency from very rare to fairly frequent, having a mild to lethal impact on the patient. All are caused by variation at a single locus. They can be classified into six categories, based on what type of chromosome they are found one and their inheritance pattern. Autosomal dominant Only one mutated copy of the gene is needed for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent. There is a 50% chance that a child will inherit the mutated gene. Many disease conditions that are autosomal dominant have low penetrance, which means that, although only one mutated copy is needed, a relatively small proportion of those who inherit that mutation go on to develop the disease, often later in life. Examples include: Huntingtons disease, Neurofibromatosis 1, HBOC syndrome, Hereditary nonpolyposis colorectal cancer Autosomal recessive Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder. Examples include: Cystic fibrosis, Sickle cell anemia, Tay-Sachs disease, Spinal muscular atrophy, Muscular dystrophy X-linked dominant X-linked dominant disorders are caused by mutations in genes on the X chromosome. Only a few disorders have this inheritance pattern.
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© Prep101 http://www.prep101.com/mcat/ Page 2 of 9 Females are more frequently affected than males, and the chance of passing on an X-linked dominant disorder differs between men and women. The sons of a man with an X-linked dominant disorder will not be affected, and his daughters will all inherit the condition. A woman with an X-linked dominant disorder has a 50% chance of having an affected daughter or son with each pregnancy. Some X-linked dominant conditions, such as Aicardi Syndrome, are fatal to boys, therefore only girls have them (and boys with Klinefelter Syndrome). Examples include: Hypophosphatemia, Aicardi Syndrome X-linked recessive X-linked recessive disorders are also caused by mutations in genes on the X chromosome. Males are more frequently affected than females, and the chance of passing on the disorder differs between men and women. The sons of a man with an X- linked recessive disorder will not be affected, and his daughters will carry one copy of the mutated gene. With each pregnancy, a woman who carries an X- linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who carry one copy of the mutated gene.
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