ATR and microcephalic primordial dwarfism: In particular, Tel1 turned out to be ortholog of the human ATM (ataxia-telangiectasia mutated) gene, whose mutation is responsible for the autosomal recessive disorder ataxia-telangiectasia (Greenwell et al., 1995; Morrow et al., 1995; Savitsky et al., 1995), whereas Mec1 was the ortholog of human ATR (ATM and Rad3-related) gene, whose mutation causes the Seckel syndrome (O'Driscoll et al., 2003).