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Question
A green stemmed tomato plant denoted by (GG) is crossed with a tomato plant with purple stem denoted by (gg).
- What colour of the stem would you expect in their F1 progeny?
- In what ratio would you find the green and purple coloured stem in plants of F2 progeny?
- What conclusion can be drawn for the above observations?
Solution
(i) All the plants in F1 progeny will be of green coloured stem.
(ii) Cross for F2 progeny is:
F2 progeny -
 |
G | g |
 |
||
| G | Gg (Green) |
Gg (Green) |
| g | Gg (Green) |
gg (Purple) |
Phenotypic ratio = Green : Purple = 3 : 1
(iii) According to the finding above, purple stems are subordinate to green stems. Thus, according to the rule of dominance, only the dominant characteristic was present in F1. Purple stem in F2 indicates that the alleles for purple stem were inherited but were not expressed in F1, nevertheless. Only in F2 under homozygous circumstances did they get expressed.
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