A homozygous tall plant (T) bearing red coloured (R) flowers is crossed with a homozygous dwarf (t) plant bearing white (r) flowers:
Give the genotype and phenotype of the plants of F1 generation.
Topic: Dihybrid cross — F1 generation
Answer
GENOTYPE: ALL are TtRr — heterozygous for both characters. PHENOTYPE: ALL are TALL with RED flowers.
Each parent is homozygous, so each produces only ONE kind of gamete — TR from the tall red parent and tr from the dwarf white one. Every offspring therefore receives T and R from one parent and t and r from the other, giving TtRr.
They all LOOK tall and red because T and R are DOMINANT and mask t and r — MENDEL’S LAW OF DOMINANCE.
THE POINT WORTH NOTING: every F1 plant CARRIES the alleles for dwarfness and white flowers, yet none shows them. The recessive alleles are MASKED, not lost — which is why they reappear in the F2 generation.