The lethal phenotype of mod(mdg4)142Δ33 is fully complemented by mod(mdg4)Z3-3401, mod(mdg4)Z3-5578 and mod(mdg4)Z3-3298, but mod(mdg4)142Δ33 fails to complement these alleles with respect to X-Y chromosome nondisjunction in male meiosis - the transheterozygotes show a high level of X-Y nondisjunction (frequency is indicated in parentheses after each allele); mod(mdg4)Z3-3401 (49.1%), mod(mdg4)Z3-5578 (37.3%) and mod(mdg4)Z3-3298 (43.5%).