Essential Genetics 6th Edition by Daniel Hartl

Exercise 2

DNA from cells of a patient with retinoblastoma was analyzed using a Southern blot with a probe for a particular restriction fragment in the RB1 gene. The result from nontumor cells and the results from cells taken from a tumor in each eye are shown in the accompanying diagram.
(a) Which band should be associated with the mutant allele and which with the nonmutant allele?
(b) How is it possible for the bands from the tumor in the left eye to be different from those from the tumor in theright eye?
(c) Explain how cells in the tumor in the right eye can have a "loss of heterozygosity" even though the bands are indistinguishable from those observed from nontumor cells.