Chapter 2, Problem 7EQ

The fungus Melampsoralini causes a disease known as flax rust. Different strains of M. lini cause varying degrees of the rust disease. Conversely, different strains of flax are resistant or sensitive to the various varieties of rust. The Bombay variety of flax is resistant to M. lini-strain 22 but sensitive to M. lini-strain 24. A strain of flax called 770B is just the opposite; it is resistant to strain 24 but sensitive to strain 22. When 770B was crossed to Bombay, all ${\text{F}}_{\text{1}}$ individuals were resistant to both strain 22 and strain 24. When ${\text{F}}_{\text{1}}$ individuals were self-fertilized, the following data were obtained:

43 resistant to strain 22 but sensitive to strain 24

9 sensitive to strain 22 and strain 24

32 sensitive to strain 22 but resistant to strain 24

110 resistant to strain 22 and strain 24

Explain the inheritance pattern for flax resistance and sensitivity to M. lini strains.