Y Chromosome Dna Testing

Until recently, the Y chromosome seemed to fulfill the role ofjuvenile delinquent among human chromosomes - rich in junk, poor in useful attributes, reluctant to socialize with its neighbors and with an inescapable tendency to degenerate...

(Mark Jobling and Chris Tyler-Smith 2003)

LINEAGE MARKERS

Autosomal DNA markers, such as the 13 core short tandem repeat (STR) loci, are shuffled with each generation because half of an individual's genetic information comes from his/her father and half from his/her mother. However, the Y chromosome and mitochondrial DNA markers that will be discussed in this chapter and the next one represent 'lineage markers'. They are passed down from generation-to-generation without changing (except for mutational events). Maternal lineages can be traced with mitochondrial DNA sequence information while paternal lineages can be followed with Y chromosome markers (Figure 9.1).

With lineage markers, the genetic information from each marker is referred to as a haplotype rather than a genotype because there is only a single allele per individual. Because Y chromosome markers are linked on the same chromosome and are not shuffled with each generation, the statistical calculations for a random match probability cannot involve the product rule. Therefore, haplo-types obtained from lineage markers can never be as effective in differentiating between two individuals as genotypes from autosomal markers that are unlinked and segregate separately from generation to generation. However, as will be discussed in this chapter and the next one, Y chromosome and mitochondrial DNA markers do have an important role to play in forensic investigations.

VALUE OF Y CHROMOSOME ANALYSIS IN HUMAN IDENTITY TESTING

The value of the Y chromosome in forensic DNA testing is that it is found only in males. The SRY (sex-determining region of the Y) gene determines maleness. Since a vast majority of crimes where DNA evidence is helpful, particularly

Figure 9.1

Illustration of inheritance patterns from recombining autosomal genetic markers and the lineage markers from the Y chromosome and mitochondrial DNA.

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