Why breeding strains of sweet peas having white flowers crossed?

#1) A white-flowered iris was crossed with a red-flowered iris. Both were true-breeding. The F1 progeny were all red. The F2 progeny were 145 red and 15 white. Suggest a genetic explanation and test it with a X2 test.





#2) Two true breeding strains of sweet peas having white flowers were crossed. All F1s had purple flowers. When the F1s were self-crossed, the F2 generation progeny were 875 with purple flowers and 725 with white flowers.





a). suggest a genetic explanation, and test it with a X2.


b) suggest a biochemical explanation

Why breeding strains of sweet peas having white flowers crossed?
Take a look at this link : http://www.bbc.co.uk/schools/gcsebitesiz...