A recessive allele in mice results in an abnormally long neck. Sometimes, during early embryonic development, the abnormal neck causes the embryo to die. An experimenter began with a population of true-breeding normal mice and true-breeding mice with long necks. Crosses were made between these two populations to produce an F1 generation of mice with normal necks. The F1 mice were then mated to each other to obtain an F2, generation. For the mice that were born alive, the following data were obtained: 522 mice with normal necks
62 mice with long necks
What percentage of homozygous mice (that would have had long necks if they had survived) died during embryonic development?