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In Search of the Sickle Cell Gene

Explore the science behind the sickle cell gene, its inheritance patterns, and the identification methods used to diagnose this autosomal recessive genetic disorder.

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In Search of the Sickle Cell Gene

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  1. In Search of the Sickle Cell Gene Terry Kotrla, MS, MT(ASCP)BB Spring 2010

  2. Introduction • Single nucleotide change in DNA can affect health and cause disease • Large number of genetic diseases have been identified. • Mutations in oncogenes and tumor suppressor genes associated with lung, colon and breast cancer (BRCA I and II).

  3. Genetics • Predicts traits inherited by offspring • Based on inheritance of two alleles, two forms of the gene, one from each parent • Can be dominant, only 1 gene necessary for expression • Or recessive, 2 identical genes necessary for expression. • Dominant allele can mask recessive gene, trait • Page 5 Figure I

  4. Sickle Cell Gene • Sickle cell anemia caused by defective hemoglobin. • Autosomal recessive genetic disorder. • Normal hemoglobin gene A • Sickle hemoglobin gene S • In normal hemoglobin A, glutamic acid is on the 6th position of the beta chain. • In sickle-cell disease glutamic acid is replaced by valine leading to the formation of sickle cells. • Single base mutation is A to T

  5. Identifying the Gene • Electrophoretic comparison of Hb S and Hb A • Slightly basic pH Hb S more positive than Hb A • Hb S will travel more slowly toward the anode. • Able to separate out • Fetal DNA can be obtained from cells obtained by amniocentesis. • Normal CCT-GAG-GAG • Point mutation changes A to G so sequence is CCT-GTG-GAG

  6. Southern Blot • Used for analysis of DNA • Perform electrophoresis to separate • Treat with HCl and NaOH. • HCL nicks double stranded DNA causing apurinic sites • NaOH disrupts intrastrand hydrogen bonds between base pairs • Results in formation of small fragments from large DNA fragments • Facilitates transfer of DNA onto nylon membrane • Add labeled probes which attach to target DNA • Analyze • http://tinyurl.com/26kzopy

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