Question

What are the genotypes of the parents in the example?
A
TTRr and ttRr
B
TtRr and TtRr
C
TTrr and TtRr
D
TTRr and TtRr

Answer 1

I don't have the example you mean, so I can't pick the correct letter yet. Could you paste the example (offspring phenotypes/genotypes or the Punnett square) or describe the observed progeny ratios?

Meanwhile, here are the expected offspring outcomes for each choice so you can match them to your example (assuming T and R are dominant alleles):

- A: TTRr × ttRr
- Gametes: (TR, Tr) × (tR, tr)
- Offspring genotypes: all Tt for T locus; R locus = 1 RR : 2 Rr : 1 rr
- Phenotypes: all show dominant T; R shows 3:1 dominant:recessive

- B: TtRr × TtRr (classic dihybrid)
- Gametes: four each (TR, Tr, tR, tr)
- Offspring phenotypic ratio (independent assortment): 9:3:3:1 for the two traits

- C: TTrr × TtRr
- Gametes: (Tr) × (TR, Tr, tR, tr)
- Offspring genotypes: equal proportions of TT vs Tt (1:1) and Rr vs rr (1:1); overall 1:1:1:1 for the four genotype combinations
- Phenotypes: all show dominant T; R shows 1:1 dominant:recessive

- D: TTRr × TtRr
- Gametes: (TR, Tr) × (TR, Tr, tR, tr)
- Offspring: T locus = TT : Tt = 1:1 (so all show dominant T); R locus = 1 RR : 2 Rr : 1 rr
- Phenotypes: all show dominant T; R shows 3:1 dominant:recessive

Send the example or the observed offspring ratios and I’ll pick the correct option.