Y-chromosomal microsatellite mutation rates: differences in mutation rate between and within loci.

We have studied 1766 father-son pairs of confirmed paternity (a total of 15 894 meioses) in nine Y-STR loci. The fathers were also analysed in five biallelic markers defining haplogroups (Hg) 1, 2, 3, 4, 9 and 16. A total of 36 fragment length mutations were observed. Our data demonstrate a significant surplus of gains and a bias towards increase in allele length upon mutational events. Overall, the mutation rate is correlated to STR repeat length, and there is a significant excess of losses in long alleles and gains in short alleles. Significant differences in mutation rate between and within loci are verified as is differences in mutation rates between haplogroups. Our findings clearly demonstrate the necessity of not only locus-specific but even allele-specific mutation rate estimates for forensic and population genetic purposes. D 2003 Elsevier B.V. All rights reserved.