Another botany "stump"?

Question

These genetics problems have my mind in a mush. Any help at all would be appreciated.

Farmer Morris has a green tobacco plant. He doesn't know the genotype of this plant. He crosses this unknown plant with a plant that is homozygous recessive for chlorophyll and gets the following results: two green plants for every two white plants. (Phenotypic ratio = 2 green: 2 white)

So, what is the genotypic ratio of the offspring?

This kind of cross would be called?

Answer 1

It's not a trick question.  There are two ways you can have a green plant - the genotype could be GG or Gg.  The recessive plant would be gg.

If the green plant was GG, it can only contribute a "G" and when you combine that with the "g" from the recessive parent, all the offspring would be Gg (green), so you know it wasn't that one.

If the green plant was Gg, half of the offspring would get a "G" and the other half "g".  So when you cross it with a white plant, half would be green (Gg) and half would be white (gg).

And it is a monohybrid cross (only one trait).

Answer 2

The cross would be monohybrid. You are only crossing for one thing or one trait, not two. Monohybrid inheritance is the inheritance of a single characteristic

Answer 3

I think this is a trick question because you will always be using 3 alleles: GG; Gg; gg and you get 30%: 70% allelic frequencies when you combine two alleles and never a 50%:50%

IF

both alleles  (GG)  =green

both alleles  (gg) =white

one allele green and one allele white (Gg) hybrid or spotted

I think the language of "green phenotype" is suspect since

* If the two alleles are the same (homozygous), the dominant phenotype they represent will be expressed and the recessive phenotype is repressed.

But if the individual carries one of each allele (heterozygous), only the dominant one will be expressed as a 3:1 phenotypic ration

* unless they have co-dominance (like blood-type).

Then instead of 3:1 ratio you'd have 1:2:1  

of 1green, 2green&white: 1white

* or incomplete dominance as in carnation colors 1:2:1 which

gives 1green:2palegreenish:1white

OUTCROSSING is a type of breeding to remove certain genotypic and phenotypic traits but to only get 50:50 is very suspicious.



The question seems vague or incomplete.