Table 1. Penetrance and Severity of T4 knockdown embryo phenotype

T4shMlc

no. oflitters

no. ofembryos

penetrance(% total embryos)

classification of severity(% total mutants)

mild

moderate

severe

15

T4shNk 21 221

140

5

37

12

mild

moderate

severe 11

43

30 14%

19%

5%

36%

51%

13%

9%

69%

22%9%

26%

4%

T4shNk and T4shMlc embryos were classified as mild, moderate or severe mutants based upon

presentation of the following diagnostic criteria: i) epicardial nodules, ii) myocardial non-

compaction, iii) morphologically abnormal myocardium (pale and necrotic appearance), iv)

displacement of the heart/extended OFT, v) vessel defects (transparency and/or failed branching), vi)

oedema and/or small embryonic size. Mutants were classified according to the number of criteria

satisfied: mild (1-2), moderate (3-4) or severe (5-6).