Chapter 16 - Lineage Markers: Y Chromosome and mtDNA Testing

Abstract

The Y chromosome (ChrY) and mitochondrial DNA (mtDNA) markers discussed in this chapter represent lineage markers. They are passed down from generation to generation without changing. Maternal lineages can be traced with mitochondrial DNA sequence information, whereas paternal lineages can be followed with Y-chromosome markers. The human Y chromosome (ChrY) is the second smallest human chromosome. Y-chromosome DNA testing is important for a number of different applications of human genetics that are given in the chapter. The chapter discusses ChrY markers, Y-short tandem repeat (STR) kits, Y-STR haplotype databases, and interpretation of Y-STR results. The chapter reviews the characteristics of mitochondrial DNA, the steps involved in obtaining results in forensic casework, and issues important to interpreting mtDNA results. Population databases play an important role in estimating the expected frequency of mtDNA haplotypes that are observed in casework when a suspect's mtDNA sequence matches that of an evidentiary sample. Having high-quality information in the database is also important in order to make a reliable estimate of the frequency for a random match. The FBI Laboratory has compiled an mtDNA population database with 4839 mtDNA profiles from 14 different populations. The European forensic mtDNA sequencing community has been actively engaged for a number of years in developing new high-quality population databases for forensic and human identity testing applications. A Korean group from Yonsei University (Seoul, Korea) has created an on-line mtDNA searchable population database called mtDNAmanager. The X chromosome has potential forensic and human identity testing applications due to its inheritance pattern. More than 30 STR markers are characterized from the X chromosome, and population studies are performed with many of these X-STRs.