Men age and die, while cells in their germline are programmed to be immortal. To elucidate how germ cells maintain viable DNA despite increasing parental age, we analysed DNA from 24 097 parents and their children, from Europe, the Middle East and Africa. We chose repetitive microsatellite DNA that mutates (unlike point mutations) only as a result of cellular replication, providing us with a natural ‘cell-cycle counter’. We observe, as expected, that the overall mutation rate for fathers is seven times higher than for mothers. Also as expected, mothers have a low and lifelong constant DNA mutation rate. Surprisingly, however, we discover that (i) teenage fathers already set out from a much higher mutation rate than teenage mothers (potentially equivalent to 77–196 male germline cell divisions by puberty); and (ii) ageing men maintain sperm DNA quality similar to that of teenagers, presumably by using fresh batches of stem cells known as ‘A-dark spermatogonia’.

A total of 103 fragments in the STR D12S391 locus were sequenced. 24 different alleles were found which can be grouped into 12 allelic classes based on the total number of repeats. The structure of this compound STR consists of blocks of (AGAT) and (AGAC) repeats with a consensus structure (AGAT)8-17 (AGAC)6-10 (AGAT)0-1. Whereas shorter alleles only have (AGAT) repeats, > 225 bp alleles are more complex, having two motifs (AGAT) and (AGAC). Population data showed that this to be a highly polymorphic STR with a heterozygosity of 0.9. This fact together with its simple structure make this STR very suitable for forensic and genetic purposes.

The tetranucleotide repeat polymorphism in the human beta-actin related pseudogene H-beta-Ac-psi-2 (ACTBP2) locus has become a widely used short tandem repeat (STR) system in paternity testing and human identification. The discrimination index of this locus has been reported to be as high as 99.65%. To study the overall variability of this locus, 222 alleles were sequenced in our laboratory. Here, we report the sequences of the 102 different alleles observed. In addition to the length polymorphism, up to ten different sequence variants for single fragment lengths have been detected.

A total of 90 alleles found in white Caucasians from North-West Germany were sequenced and 26 alleles chosen to construct a uniform and reliable allelic ladder for the STR system ACTBP2 (SE33). In addition 3 new aspects concerning the sequence structure were observed. Population studies were carried out on white Caucasians (n = 278) from North-West Germany using the new improved ladder. A total of 24 alleles and 14 "interalleles" were found and reproducible results obtained. No significant deviation from Hardy-Weinberg-equilibrium could be observed.

A modification to the DNA extraction method "preferential lysis" (Gill et al. 1985) is proposed which can be applied to DNA mixtures of vaginal cells and spermatozoa. In mixtures with a low sperm content the further loss of sperm DNA caused by the extraction can be avoided by using "mild preferential lysis". Amplification by PCR (polymerase chain reaction) then yields sufficient DNA to be able to identify both components in the mixture.