A homozygous dominant tall pea plant bearing red flowers (TTRR) is crossed with a homozygous recessive dwarf pea plant bearing white flowers (ttrr).
What is the phenotype and genotype of F1 individuals?
Topic: Dihybrid cross — F1 generation
Answer
PHENOTYPE: ALL the F1 plants are TALL with RED flowers. GENOTYPE: ALL are TtRr (heterozygous for both characters).
Each parent is homozygous, so each can produce 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. This is 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.