A snapdragon plant that bred true for white petals was crossed with a plantthat
ID: 63579 • Letter: A
Question
A snapdragon plant that bred true for white petals was crossed with a plantthat bred true for purple petals, and all the F1s had white petals. The F1 wasselfed. Among the F2, three phenotypes were observed in the followingnumbers:
White 480
Solid purple 122
Spotted purple 38
a. Propose an explanation for these results, showing genotypes of allgenerations.
b. A white F2 plant was crossed with a solid purple F2 plant, and theprogeny were 250 white: 123 solid purple : 128 spotted purple. Whatwere the genotypes of the two F2 plants?
Explanation / Answer
a. This is an effect of dominant epistasis. Cross between plants bred true for white petals (WWPP) and a plant that bred true for purple petals (wwpp), will have all offspring with the WwPp genotype. ----------> F1 generation.
Cross between F1 will be, WwPp* WwPp =
WWPP (1/16, white); WWPp (2/16, white), WWpp (1/16, white), WwPP (2/16, white), WwpP (4/16, white), Wwpp (2/16, white), wwPP (1/16, solid purple), wwPp(2/16, solid purple), wwpp (1/16, spotted purple).
The phenotypic ratio is, 12: 3: 1 (White: solid purple: spotted purple).
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