Dihybrid cross 4:4:4:4 phenotype

I know this is easy (as all are Punnitt squares) but it has me stumped. What dihybrid cross will give a phenotype of 4:4:4:4:. Tall is dominant to short. Red is dominant to yellow.

Assuming this isn’t homework…

IANAGeneticist, so I’m not sure of the conventional symbology, but assuming

T=tall, t=short
R=red, r=yellow

the desired cross would be

TtRr X ttrr

That is, heterozygous in both traits for one parent, and homozygous recessive for both traits for the other.

I think that’s right.


Thanks. No it wasn’t homework. I was quizzing my daughter (who has a biology test tomorrow) on mono and dihybrid crosses. I ask the genotypes that yeild
9:3:3:1, or 16:0:0:0, no problem. I ask 4:4:4:4 which I vaguely remembered from college genetics (yes, college genetics used to use Punnitt squares) and she doesn’t know, tries to figure it out, says it is impossible, I try to figure it out, and can’t do it either. Hence the request.

I believe RickG has it right.

The heterozygous parent will produce four types of gametes, TR, Tr, tR, and tr, while the homozygous will produce only one, tr. The cross will thus produce four kinds of phenotypes in equal ratios: TtRr, Ttrr, ttRr, and ttrr.