A minimum of 28 genotype-confirmed progeny from heterozygous intercrosses were required to assess viability at the stage studied. A line is classified as lethal if no homozygous embryos are recovered. Lines producing fewer than 13% homozygotes were considered to be subviable, otherwise the line was classified as viable. No homozygotes from 28 progeny gives 95% confidence that the probability of homozygote survival was ≤ 40% based on exact binomial probability calculations.

The E9.5 data is based on an average of 6 litters per line, and a minimum of 4 litters were used to make each call. During the course of the study two slightly different tests have been used to assess viability, which are referred to as 'Total' and 'Confirmed'. The more recent 'Confirmed' test includes additional PCR steps to assess the sex of the embryos, and viability was assigned on the basis of the 'Confirmed' data if that was available otherwise the 'Total' data was used.

All the data used to determine the viability is available in the TSV file. The viability is listed as 'Not Assigned' if not enough embryos were collected to determine viability, please see the TSV file for details.