A recessive allele in mice results in an abnormally long nec

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?

Solution

Assuming that the gene coding for the normal neck is L and the gene coding for the long neck is l; and L is dominant over l. The cross between true breeding mice LL and ll would produce Ll mice (F1 generation)

Self-cross of F1 generation will result in the offspring with the following genotypes:

Ll* Ll ---> L_ (3/4, normal neck mice), ll (1/4, long neck mice)

It is given that the number of mice with normal neck are, 522, which indicates 3/4th of the population. So, the total number of expected mice are approximately 700.

The expected mice with long necks are, 1/4*700 = 175

The mice survived are 62.

The mice died are, 175-62 = 113

Thus, 113/700 * 100 = 16.14% of homozygous mice died during embryonic development.