STR melting curve analysis as a genetic screening tool for crime scene samples

In this proof-of-concept study, high-resolution melt curve (HRMC) analysis was investigated as a postquantification screening tool to discriminate human CSF1PO and THO1 genotypes amplified with mini-STR primers in the presence of SYBR Green or LCGreen Plus dyes. A total of 12 CSF1PO and 11 HUMTHO1 genotypes were analyzed on the LightScanner HR96 and LS-32 systems and were correctly differentiated based upon their respective melt profiles. Short STR amplicon melt curves were affected by repeat number, and single-source and mixed DNA samples were additionally differentiated by the formation of heteroduplexes. Melting curves were shown to be unique and reproducible from DNA quantities ranging from 20 to 0.4 ng and distinguished identical from nonidentical genotypes from DNA derived from different biological fluids and compromised samples. Thus, a method is described which can assess both the quantity and the possible probative value of samples without full genotyping.     

中国汉族人群17个Y-STR基因座突变情况分析

目的 调查分析17个Y-STR基因座等位基因突变的情况.方法 收集中国汉族人群867对父子共1 649份男性血样本.采用YfilerTM复合扩增试剂盒进行17个Y-STR基因座分型,共检测出14 739次等位基因传递,统计各基因座发生等位基因突变的频率.结果 在17个基因座中发现涉及13个基因座共41次突变,其中一步突变40次(97.6％),两步突变1次(2.4％);突变共涉及40对父子,其中39对仅1个基因座发生突变(97.5％),1对同时有2个基因座发生突变(2.5％);平均突变率为2.8×10-3(95％CI 2.0～3.8×10-3).等位基因突变时获得重复单位数19次,丢失重复单位数22次,两者比例接近.结论 中国汉族人群Y-STR基因座突变可涉及多数基因座,突变率在2.8×10-3左右,在数据库的建立与应用中应重视,注意采用相关方法进行甄别.     

Development of a rapid, 96-well alkaline based differential DNA extraction method for sexual assault evidence

We present a rapid alkaline lysis procedure for the extraction of DNA from sexual assault evidence that generates purified sperm fraction extracts that yield STR typing results similar to those obtained from the traditional organic/dithiothreitol differential extraction. Specifically, a sodium hydroxide based differential extraction method has been developed in a single-tube format and further optimized in a 96-well format. The method yields purified extracts from a small sample set (∼2-6 swabs) in approximately 2 h and from a larger sample set (up to 96 swabs) in approximately 4 h. While conventional differential extraction methods require vigorous sample manipulation to remove the spermatozoa from the substrate, the method described here exploits the propensity of sperm to adhere to a substrate and does not require any manipulation of the substrate after it is sampled. For swabs, sample handling is minimized by employing a process where the tip of the swab, including the shaft, is transferred to the appropriate vessel eliminating the need for potentially hazardous scalpels to separate the swab material from the shaft. The absence of multiple handling steps allows the process to be semi-automated, however the procedure as described here does not require use of a robotic system. This method may provide forensic laboratories a cost-effective tool for the eradication of backlogs of sexual assault evidence, and more timely service to their client agencies. In addition, we have demonstrated that a modification of the procedure can be used to retrieve residual sperm-cell DNA from previously extracted swabs.     

Challenging DNA: Assessment of a range of genotyping approaches for highly degraded forensic samples

It is common in forensic casework to encounter highly degraded DNA samples from a variety of sources. In this category bone and teeth samples are often the principal source of evidential material for criminal investigations or identification of long-deceased individuals. In these circumstances standard STRs are prone to fail due to their long amplicon sizes (since DNA becomes progressively more fragmented as it degrades). To successfully resolve such cases alternative markers can be used and until recently the only other tool available was mitochondrial DNA, which despite being more resistant to degradation, is much less informative. A rapidly developing approach to analyzing degraded DNA is the typing of loci from short-amplicon PCR products based on markers such as mini-STRs and autosomal SNPs. We have performed an analysis of several cases with naturally degraded DNA using established STRs plus mini-STRs and autosomal SNPs in order to make an objective comparison of the performance of each method using challenging DNA. The main aim was to establish the benefits and drawbacks of each marker set to help the practitioner choose the DNA analysis method most suited to the circumstances of each case.