Midterm 2. Study Guide - Study guide for the second midterm...

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Study guide for the second midterm exam, BME/BIO 80H, The Human Genome From lecture 6 1. Understanding and interpreting Human Pedigrees  See attached page. 2. Recognizing the different patterns of inheritance Autosomal recessive traits o For rare or relatively rare traits, most affected individuals have unaffected parents o All children of two affected homozygous individuals are affected  o The risk of an affected child from a mating of two heterozygote is 25% o Because the trait is autosomal, it is expressed in both males and females, who are affected  in roughly equal numbers, both male and female parent will transmit the trait o In pedigree involves rare traits, the unaffected (hterozycous) parents of an affected  (homozygous) individual may be related to each other.  o Examples: cystic fibrosis, sickle cell Autosomal Dominant o Every individual should have at least one affected parent unless the gene has a high  mutation rate o Because most affected individuals hare heterozygous with a homozygosis recessive  (unaffected) spouse, each child has a 50 percent chance of being affected o Because traits are autosomal, males and females have an equal chance of being affected o Two affected individus may have unaffected children, again because most affected  individuals are heterozygous o The phenotype in homozygous dominant individuals is often more severe than the  heterozygous phenotype.  o Examples; Marfan syndrome X-Linked Dominant Traits o Affected males produce all affected daughters and no affected sons o All heterozygous affected female will transmit the trait to half of her children and sons and  daughters are affected equally o On average, twice as many daughters as sons are affected o Examples: hypohosphatema: those affected have low phosphate levels in blood and skeletal  deformities.  X-linked recessive traits o Hemizygous males and homozygous females are affected o Phenotype expression is much more common in males than in females o Affected males get the mutant alleles from their mothers and transmit it to all their daughters  but not to any of their sons o Daughters of affected males are usually heterozygous and therefore unaffected, but sons of  heterozygous females have a 50% chance of receiving the recessive gene o Examples color blindness, muscular dystrophy 3. Duchenne Muscular Dystrophy Symptoms and prognosis o Progressive weakening & wasting of muscle o Sympotoms appear in 1 st  5 years of life, no cure fatal by age 20 Frequency/population
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o 1/3500 males in the us Biology- o Dystrophin protein not ade o Dystrophin stabilizes the membrane of muscle cells o
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