Figure 2.

Schematic representation of the Y chromosome and the current microdeletion model (Repping et al., ²⁰⁰²). Repetitive sequences (colour coded palindromes) explain the origin of deletions in the AZFbc region by homologous recombination between identical sequences. The location of the STS primers suggested by the present guidelines is indicated by dashed lines. As four copies of the DAZ gene are normally present on the Y chromosome, the STS primers sY254, sY255 amplify four loci in AZFc. The AZFc (b2/b4) deletion is by far the most frequent type (∼80%) of Y-chromosomal microdeletions found in men with severe oligo/azoospermia.