necessary self examination that provokes a major change in the direction ofyour professional life. If so, so be it. It is good that such changes should be made while time is still on our side. Otherwise we are in danger of joining what Thoreau thought to be the majority of men, who \"lead lives ofquiet desperation.\" So ifyou haven't already done so start planning your sabbatical now-and don't forget to tell your partners and your spouse.

https://www.bmj.com/content/bmj/295/6599/646.full.pdf

Methods in molecular medicine.

Until recently, the Y chromosome seemed to fulfil the role of juvenile delinquent among human chromosomes — rich in junk, poor in useful attributes, reluctant to socialize with its neighbours and with an inescapable tendency to degenerate. The availability of the near-complete chromosome sequence, plus many new polymorphisms, a highly resolved phylogeny and insights into its mutation processes, now provide new avenues for investigating human evolution. Y-chromosome research is growing up.

/pdf/the-human-y-chromosome-an-evolutionary-marker-comes-of-age-2nz5mvksa5.pdf

The human Y chromosome: an evolutionary marker comes of age

In less than half a century, molecular markers have totally changed our view of nature, and in the process they have evolved themselves. However, all of the molecular methods developed over the years to detect variation do so in one of only three conceptually different classes of marker: protein variants (allozymes), DNA sequence polymorphism and DNA repeat variation. The latest techniques promise to provide cheap, high-throughput methods for genotyping existing markers, but might other traditional approaches offer better value for some applications?

The evolution of molecular markers — just a matter of fashion?

The characterization of genetic variation at the DNA level has generated significant advances in gene and disease mapping1, and in the forensic identification of individuals2–6. The most common method of DNA analysis, that of restriction fragment length polymorphism (RFLP), requires microgram amounts of relatively undegraded DNA for multi-locus typing, and hundreds of nanograms for single-locus comparisons7. Such DNA frequently cannot be obtained from forensic samples such as single hairs and blood stains, or from anthropological, genetic or zoological samples collected in the field. To detect polymorphic DNA sequences from single human hairs, we have used the polymerase chain reaction (PCR), in which specific short regions of a gene can be greatly amplified in vitro8–10 from as little as a single molecule of DNA10. We have detected genetically variable mitochondrial and nuclear DNA sequences from the root region of shed, as well as freshly-plucked, single hairs; mitochondrial DNA (mtDNA) sequences have been detected in a sample from a single hair shaft. We have used three different means of DNA typing on these samples: the determination of amplified DNA fragment length differences, hybridization with allele-specific oligonucleotide probes, and direct DNA sequencing.

DNA typing from single hairs

Over the past decade, the human identity testing community has settled on a set of core short tandem repeat (STR) loci that are widely used for DNA typing applications. A variety of commercial kits enable robust amplification of these core STR loci. A brief history is presented regarding the selection of core autosomal and Y-chromosomal STR markers. The physical location of each STR locus in the human genome is delineated and allele ranges and variants observed in human populations are summarized as are mutation rates observed from parentage testing. Internet resources for additional information on core STR loci are reviewed. Additional topics are also discussed, including potential linkage of STR loci to genetic disease-causing genes, probabilistic predictions of sample ethnicity, and desirable characteristics for additional STR loci that may be added in the future to the current core loci. These core STR loci, which form the basis for DNA databases worldwide, will continue to play an important role in forensic science for many years to come.

https://www.sjsu.edu/people/steven.lee/courses/JS111FLUOR/s0/Butler2006JFS_coreSTRreview.pdf

Genetics and genomics of core short tandem repeat loci used in human identity testing.

Many highly polymorphic minisatellite loci can be detected simultaneously in the human genome by hybridization to probes consisting of tandem repeats of the 'core' sequence. The resulting DNA fingerprints produced by Southern blot hybridization are comprised of multiple hypervariable DNA fragments, show somatic and germline stability and are completely specific to an individual. We now show that this technique can be used for forensic purposes; DNA of high relative molecular mass (Mr) can be isolated from 4-yr-old bloodstains and semen stains made on cotton cloth and digested to produce DNA fingerprints suitable for individual identification. Further, sperm nuclei can be separated from vaginal cellular debris, obtained from semen-contaminated vaginal swabs, enabling positive identification of the male donor/suspect. It is envisaged that DNA fingerprinting will revolutionize forensic biology particularly with regard to the identification of rape suspects.

Forensic application of DNA 'fingerprints'.

b) The cost advantages for SNPs are not obvious at present. Although platforms and biochemistry are being developed that enable extremely high throughput, this research is carried out primarily for the pharmaceutical industry for drug discovery and is not directly applicable to forensic use. This is because forensic scientists have to contend with small-degraded samples. There are substantial difficulties associated with building large multiplexes. It is easy to be swept along with the tide of new technology, simply because it is something different. However, we must take a step back and objectively evaluate the reasons for implementing a new system. New does not necessarily mean better or applicable. We should remember that SNPs were initially developed for forensic application in the late 1980s and early 1990s, but were superseded by STRs because of their marked superiority – the discussion is not new. Since then, the SNP platform and biochemistry have undergone development to merit fresh consideration within the context of high throughput and associated reduced costs. However, concurrent parallel research continues to miniaturise and to reduce the costs of STR platforms as well. Consequently, more time is needed to assess the new developments.

An assessment of whether SNPs will replace STRs in national DNA databases--joint considerations of the DNA working group of the European Network of Forensic Science Institutes (ENFSI) and the Scientific Working Group on DNA Analysis Methods (SWGDAM).

Many highly polymorphic minisatellite loci can be detected simultaneously in the human genome by hybridisation to probes consisting of tandem repeats of the ‘core’ sequence. The resulting DNA fingerprints produced by Southern blot hybridisation are comprised of multiple hypervariable DNA fragments, show somatic and germline stability and are completely specific to an individual. DNA of high molecular weight can be isolated from blood and semen stains up to 4 years old. Sperm nuclei can be separated from vaginal debris and the sperm DNA examined in isolation, allowing the positive identification of rapists. Correspondingly, vaginal DNA can be isolated from extracts of penile swabs. DNA can also be isolated from extracts of buccal swabs. A blind trial involving 43 blood samples, 11 bloodstains and 11 semen stains has been successfully carried out. It is envisaged that genetic fingerprinting will shortly form an important part of casework procedure in forensic science laboratories.

An evaluation of DNA fingerprinting for forensic purposes

The National DNA Database

A computerised system has been used to store DNA profiles from 3 hypervariable loci. This initial survey illustrates that band matching is only possible after analysis of the errors associated with electrophoretic systems. A number of databases have been constructed with the three probes investigated and two methods of frequency determination, ‘binning’ and ‘sliding window’ fitting, have been compared.

David J. Werrett

Papers

Forensic application of DNA 'fingerprints'.

An assessment of whether SNPs will replace STRs in national DNA databases--joint considerations of the DNA working group of the European Network of Forensic Science Institutes (ENFSI) and the Scientific Working Group on DNA Analysis Methods (SWGDAM).

An evaluation of DNA fingerprinting for forensic purposes

The National DNA Database

The analysis of hypervariable DNA profiles: problems associated with the objective determination of the probability of a match