Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 40

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 F 1 generation of mice with normal necks. The F 1 mice were then mated to each other to obtain an F 2 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