Question
Fri February 24, 2012 By:

The genotype of green stemmed tomato plants is donated as GG and that of purple stemmed tomato plants as gg.When these two are crossed. (1)What colour of stem would you expect in their F1 progeny? (2) Give the percentage of purple stemmed plants if F1 plants self pollinate. (3)In what ratio would you find the genotypes GG and Gg in the F2 progeny?

Expert Reply
Sat February 25, 2012
The dominant trait is denoted by capital letters (here G) and the recessive trait by small letters. (here g)
If any dominant gene is present in the organism, the character expressed will be the dominant one.
Eg- If the organism carries Gg gene, the character expressed will be green stem and not purple stem even though the purple gen (g) is present. This is because the recessive cgene gets masked by the dominant one.
i) In F1, the progeny would be Gg, so all would be green stemmed.
ii) If F1 plants self pollinate,
Parents             Gg     x     Gg
Gametes        G     g          G    g

  

 

G

g

G

GG  (Green)

Gg  (Green)

g

Gg   (Green)

gg   (purple)

Ratio of GG: Gg:gg = 1:2:1
Percentage of purple stemmed plants = 25%
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