top2a , but not top2b , is expressed pre-MZT. RT-PCR of wt embryos (A-B) and real time PCR of offspring from blm carriers (C-D) shows that maternal top2a (A, C), but not top2b (B, D), is present pre-MZT at 8- and 16-cell stages. top2a transcript levels decrease in blm siblings from 27 hpf to 3 dpf, and the expression in blm mutants is always significantly lower (C). The levels of top2b transcript also decrease in wildtype siblings from 27 hpf to 3 dpf, and although top2b levels in blm mutants and siblings is similar at 27 hpf, top2b is dramatically reduced in the mutants by 2 dpf (D). Error bars represent the standard error of the mean. At 8-cell, 16-cell, 4 hpf and 10 hpf stages mutant and wild type offspring are pooled. In graphs light blue (C) and light green bars (D) represent pooled wiltype and mutant embryos; dark blue/green bars represent blm mutants and white bars represent wildtype larvae.