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Abstract Y-chromosome testing played an important role in forensic DNA testing by answering some interesting historical questions like historical human migration patterns through male lineages. STR markers on the Y chromosome (Y-STRs) importance clearly observed in that they have qualities that are distinct from autosomal markers and are useful for human identification. DNA regions of Y chromosome with repeat units of 2-6 bp in length are called microsatellites or Y chromosome short tandem repeats (Y-STRs) are very effective for human identification purposes. DNA direct polymerase chain reaction (PCR) amplification is a sample processing method in which an evidence or substrate punch is added directly to the PCR without prior extraction. This resulted in an improvement in the results of the genetic profiling data for these samples. Direct PCR reduces loss of DNA because it does not involve sample transfer or sample purification. This increases the sensitivity of PCR, highlighting its benefit for latent DNA samples. The present study was carried out to save the cost and time required for obtaining DNA profile of Y chromosome through application of direct PCR method. Direct PCR method also has the ability to give high quality of DNA profile and less cross contamination. When applying the direct PCR method to hair samples that were taken from people who do not normally use any chemicals or hair waxes, positive results were obtained more than the same samples that were exposed in the routine extraction method. There was also a preference for direct PCR method when used on one hair sample rather than three hairs in contrast to routine extraction method which requires sufficient amount of DNA to give the required results. When using the direct PCR method on hair samples obtained from individuals who commonly use hair waxes, they gave negative results. However, when treated with some commercially available detergents and physical treatment (gentle pull of the outer layer of hair follicles), the scale of peak heights in all loci were increased. The samples treated with the soap foam treatment gave the best results than other treatments. The results were consistent when use one to three hair samples. Since most people currently use hair waxes and chemicals, this test is of great importance in criminal casework to obtain the DNA profile of Y chromosome from the hair samples taken from these people. The results of the Y chromosome DNA profile for (10) families; each family has (5) males were obtained to reveal the extent of convergence between these males from the same family. Also, the extent of divergence and convergence between the families that was included in this study, the effect of geographic nature and environmental conditions on the results of the profiling data of these families. In this study, it was possible to determine in certain percentages the extent of the divergence and convergence between families as well as the geographical dimensions and genealogy through the short tandem repeats on the Y chromosome. There are tends for sons to their father or mother, as previous studies have indicated about this tendency (dominant / recessive theory). By paternity test, sons showed their tendency to their father or mother, as this was determined by the scale of peak heights in the heterozygote genetic loci. The correlation coefficients have revealed the tendency of the sons to their father or mother in the same family. These genetic tendencies refer to the physical and genetic characteristics that a child can acquire from one parent to the other. These results are also an indicator of genetic mutations and tendencies toward violence that have been inherited from any of the parents. DNA (Deoxyribonucleic Acid) is the genetic material present in every cell of the human body. A child receives half of his or her genetic material (DNA) from the biological mother, and half from the biological father. During DNA testing, the genetic characteristics of the child are compared to those of the mother. characteristics that cannot be found in the mother must have been inherited from the father. The genetic analyses in paternity and in forensic casework are based on the detection of short tandem repeats (STRs), which are small sequences of DNA made up of repeating units of 2–6 nucleotides. STR markers located on autosomal chromosomes transmit to the next generation in the Mendelian inheritance model where biological offspring shares one allele from father and the other from mother on all the tested loci. For each locus, one allele from the child must match one of the mother’s allele for that region. The child’s other allele will match with the biological father. It is the principle that is applied for determination of parentage. Current study was performed on 75 individuals who donated some tissues voluntarily, which 125 biological samples were taken from them and were divided into; 60 hair samples for Y chromosome direct PCR, 50 blood and saliva samples for Studying the relationship between males of the same family and other ten families through the test of Y chromosome, and 15 blood and saliva samples to study the tendency of children to their father or mother and its relationship to morphological and physical characteristics through the results of DNA STRs in paternity test. Samples applied to different experiments were subjected to a group of experiments which include: 1- DNA extraction. 2- Amplification of certain microsatellites. 3- Separation and detection of STR amplicons. 4- DNA genotyping. - In addition to the samples that applied to the direct PCR method, and compared with the samples that loaded by routine extraction method. |