Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 9

Let's suppose an X-linked gene in mice exists as two alleles, which we will call B and b. X-chromosome inactivation, a process in which one X chromosome is turned off, occurs in the somatic cells of female mammals (see Chapter 5). Allele B encodes an mRNA that is 900 nucleotides long, whereas allele b contains a small deletion that shortens the mRNA to a length of 825 nucleotides. Draw the expected results of a Northern blot using mRNA isolated from somatic tissue of the following mice:
Lane 1. mRNA from an X b Y male mouse
Lane 2. mRNA from an X b X b female mouse
Lane 3. mRNA from an X B X b female mouse. Note: The sample taken from the female mouse is not from a clone of cells. It is from a tissue sample, like the one shown at the beginning of the experiment of Figure 5.6.FIGURE 5.6 Evidence that adult female mammals contain one X chromosome that has been permanently inactivated.
Starting material: Several small skin samples taken from a woman who was heterozygous for the fast and slow alleles of G-6-PD.