Table 2. Frequency of different morphological defects in embryos at E8.5 from matings of Tbx20 ^+/- ; Tbx3 ^+/- double heterozygotes^*.

		Genotypes
Stage	Morphology	wt**	Tbx20 -/- ; Tbx3 +/+	Tbx20 -/- ; Tbx3 +/-	Tbx20+/+ ;Tbx3 -/-	Tbx20 +/- ; Tbx3 -/-	Tbx20 -/- ; Tbx3 -/-
E8.5	Normal	89	3***	2***	1***	0	1***
	Abnormal. looping	0	14	14	0	0	0
	Abnormal looping / delay	0	3	3	0	0	3
	Abnormal looping / dead	0	2	0	0	0	0
	Delay	6	1	6	7	4##	3
	Dead#	1	0	3	0	0	1
Total (n=167)		96	23	28	8	4	8

^* Double heterozygotes were either intercrossed or crossed to single heterozygotes.

^** wt, wild type; this group includes wild type and heterozygotes for one or both alleles.

^*** Embryos were at the cardiac crescent stage, prior to heart looping.

^# Approximate time of death between E8.0 and E8.5; too degenerate to score for heart phenotype.

^## One of these embryos had a yolk sac defect.