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 XbY male mouse
Lane 2. mRNA from an XbXb female mouse
Lane 3. mRNA from an XBXb female mouse. 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.