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inheritance question

hi im stuck on this question:

A recessive mutant of the gene which is responsible for cholorophyll synthesis in the tomato plant causes the plant to be colourless when present in the homozygous condition. Such a plant dies as a seedling after it has used up its supplies of food. In the heterozygous state the mutant produces a pale plant but one that survives.
A normal green tomato plant was crossed with a pale heterozygote and the seeds formed from the cross were collected. These seeds were subsequently planted and a number of tomato plants reared which were self-pollinated. once again the seeds were collected and a further generation of plants grown.
the ratio of normal green to pale plants in this generation was found to be 5:2. How can these results be explained?

Let G be normal green tomato plant
Let g be the recessive mutant

Parents: GG * Gg

F1: GG, GG, Gg, Gg

F2: GG, Gg, gg in the ratio 9:6:1

can someone please tell me where i have gone wrong. thanks.

Reply 1

Wangers

have you understood the theory of Monohybrid crosses?.

I havent done the calculation, but that 5:2 ratio definatly is not monohybrid or dihybrid, is it possibly co-dominant?

Sorry I'm a bit rusty and as exciting as plummet squares are....

Reply 2

iainmacn

Two types of F1 - GG and Gg

GG self-polinated with GG will give 4 possible F2, all GG

Gg with Gg gives GG, Gg, Gg and gg

gg dies as a seedling (see the question) so that leaves you with 5 x GG and 2 x Gg