A new variety of campion has been discovered that has either red or white flower

Question

A new variety of campion has been discovered that has either red or white flowers. Campions are dioecious plants that have male and female forms. As well as autosomal chromosomes, campion has a pair of sex chromosomes. Female forms have two X chromosomes and male forms have an X and Y chromosome. Red flowered male plants were crossed to white flowered female plants. The progeny from this cross were examined and it was found that there were only white-flowered male plants and red-flowered female plants.

a) What can you deduce from these results?

b) Using the progeny from the cross described above, suggest an experiment to test whether all possible combinations of gender and colour can occur.

Explanation / Answer

a) The sex of these plants is determined by a pair of sex chromosomes and flower colour is also determined by these sex chromosomes, and red is dominant to white.

b) In the original cross the females were XwXw and the male X+Y (w is a mutation that confers white flowers and wild-type confers red flowers). The progeny from this cross were X+Xw and XwY. A cross between these two individuals should generate a 1:1:1:1 ratio of red-flowered females to white flowered females to red-flowered males to white-flowered males, assuming that all possible combinations are viable.

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