PIGQ and neoplasm: To investigate whether any of the ten Gpi1−/−↔Gpi1c/c chimaeras could produce functional gametes from homozygous Gpi1−/− null germ cells, they were crossed to albino Gpi1c/c mice, as shown in Fig. 1B. Chimaera 53 developed a tumour and was culled when it was pregnant with its first litter; all eight fetuses had unpigmented eyes and were GPI1C (expected genotype, Gpi1c/c).