Chapter 15, Problem 17P

A form of male sterility in corn is inherited maternally. Marcus Rhoades first described this cytoplasmic male sterility by crossing female gametes from a male sterile plant with pollen from a male fertile plant. The resulting progeny plants were male sterile.

a.	Diagram the cross, using different colors and shapes to distinguish between nuclear (lines) and cytoplasmic(circles) genomes from the male sterile (one color) and male fertile (another color) strains.
b.	Female gametes from the male sterile progeny were backcrossed with pollen from the same male fertile parent of the first cross. The process was repeated many times. Diagram the next two generations including possible crossover events.
c.	What was the purpose of the series of backcrosses? [Hint: Look at your answer to part (b) and think about what is happening to the nuclear genome.] Why could Rhoades interpret these results as a demonstration of cytoplasmic male sterility?