Mendel's Monohybrid Cross

• Gregor Mendel — pea plant experiments; laws of inheritance.
• Monohybrid cross — one trait (e.g. tall vs dwarf); TT × tt → F₁ all Tt.
• F₂ generation — Tt × Tt → phenotypic ratio 3:1 (tall:dwarf).
• Genotypic ratio — 1 TT : 2 Tt : 1 tt.
• Dominant (T) masks recessive (t) in heterozygote.

1. Factors (genes) — Mendel's unit of inheritance; alleles T and t for height.
2. Homozygous — TT or tt; heterozygous — Tt.
3. P generation — pure tall (TT) × pure dwarf (tt).
4. F₁ — all tall (Tt) — tall dominant.
5. F₂ self-cross — Punnett square 3 tall : 1 dwarf phenotypically.
6. Gametes — each carries one allele; Tt produces T and t gametes.
7. Segregation — alleles separate during gamete formation (Law of Segregation).
8. Phenotype — observable trait; genotype — genetic makeup.
9. Pea plant advantages — distinct traits, self-pollination, short generation time.
10. NCERT Punnett square — must draw for monohybrid cross exam questions.

Monohybrid cross: F₁ Tt × Tt — find F₂ ratios

Gametes from Tt: 50% T, 50% t each parent.
Punnett: TT, Tt, Tt, tt
Phenotype: 3 tall : 1 dwarf (75% : 25%)
Genotype: 1 TT : 2 Tt : 1 tt
Conclusion: Mendel's 3:1 phenotypic ratio in F₂.

• Counting 3:1 as genotypic ratio (genotypic is 1:2:1).
• Misconception: dominant allele more common in population (not necessarily).
• Forgetting gametes carry one allele each.
• Confusing F₁ with F₂ generation labels.
• Drawing Punnett with two alleles per gamete (should be one).

• Define monohybrid cross.
• F₁ ratio when TT crosses tt?
• Write F₂ phenotypic ratio.
• Difference between genotype and phenotype?

Open the Practice tab for graded questions on Mendel's Monohybrid Cross.