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Polymorphism & Restriction Fragment Length Polymorphism (RFLP)

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Presentation on theme: "Polymorphism & Restriction Fragment Length Polymorphism (RFLP)"— Presentation transcript:

1 Polymorphism & Restriction Fragment Length Polymorphism (RFLP)

2 Genome Variation Definition: –In 2 non-related individuals: 0.1% genome variation (1 in each 1500 bases) PolymorphismMutation Clinical effect Clinically harmless (No effect on phenotype Potentially harmful (results in genetic disease incidence ≥ 0.1% rare:  0.1%

3 Polymorphism Polymorphism: is a variation in nucleotide sequence from one individual to another, occurring in the non-coding regions of DNA. RFLP: is a genetic variant that can be examined by cleaving the DNA into fragments (Restriction fragments) with a RE. The length of the restriction fragments is altered if the genetic variant alters the DNA so as to create or abolish a site of RE cleavage. It can be used to detect human genetic variations, e.g. in prospective parents or in fetal tissue 2 types of DNA variation result in RFLP: SNP VNTR Considered markers, which, in most cases, have NO known effect on the structure or rate of production of any particular protein.

4 Single Nucleotide Polymorphism (SNP; 90% of human genome variation)

5 Variable Number of Tandem Repeats (VNTR) Tandem repeats: –short sequences of DNA at scattered locations in the genome –Repeated in tandem (one after another) –The # of these units varies from person to person, but is unique for any given individual –Serves as a molecular fingerprint

6 Variable Number of Tandem Repeats (VNTR) VNTR loci: sites in genome that are frequently showing VNTR, important in DNA fingerprinting analysis (e.g. in forensic & paternity identity)

7 RFLP of VNTR

8 Prenatal Diagnosis It is recommended if there is a history of severe genetic disease, (affected previous child or near relative) Its aim is to determine the presence of the disorder in a developing fetus Methods available: 1.Visualization of the fetus e.g. by Ultrasound or fetoscopy: –If the genetic abnormality → gross anatomic defects e.g. neural tube defect 2.Amniotic fluid biochemical analysis: –e.g. level of  fetoprotein (increase in open neural tube defects, & low in Down syndrome. –Fetal cells in amniotic fluid or in chrorionic villi biopsy: Karyotyping: the morphology of the metaphase chromosomes (e.g trisomies, translocations →abnormal length of chromosome 3.Fetal DNA analysis: (the most detailed genetic picture; DNA from WBC, Amniotic fluid, or Chorionic villi –DNA has to be amplified first: In the past: cell culture Now: PCR

9 Examples of diseases diagnosed prenatally Sickle cell anemia: Could be diagnosed prenatally by: I- Electrophoresis analysis of the amount & type of Hb obtained by hemolyzing fetal blood 1- risk in obtaining fetal blood 2- Late detection (2 nd trimester) 2- Fetal DNA then do RFLP: Advantages: 1- Safe 2- early detection

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12 RFLP in a family with a child affected by PKU


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