7 Mendel's Traits (Dominant → Recessive)

TRAP: Yellow seed but GREEN pod (dominant)!

The Must-Know Ratios

• Monohybrid F2 (complete dominance): 3:1 phenotypic | 1:2:1 genotypic
• Monohybrid F2 (incomplete/co-dominance): 1:2:1 phenotypic = genotypic
• Dihybrid F2 (independent): 9:3:3:1
• Dihybrid test cross: 1:1:1:1
• Monohybrid test cross (Tt): 1:1

Modified Ratios

9:7 | 9:3:4 | 12:3:1 | 15:1 | 13:3 — ALL sum to 16

ABO Blood Group Quick Reference

• $I^A$ $I^A$ or $I^A$ i = Group A (A antigen, Anti-B)
• $I^B$ $I^B$ or $I^B$ i = Group B (B antigen, Anti-A)
• $I^A$ $I^B$ = Group AB (Both antigens, No antibodies = Universal Recipient)
• ii = Group O (No antigens, Both antibodies = Universal Donor)
• Dominance: $I^A$ = $I^B$ > i

Key Distinctions

Scientists to Remember

• Mendel → 3 laws, Pisum sativum, 1860s
• Sutton + Boveri → Chromosomal Theory, 1902
• Morgan → Linkage, Drosophila, Nobel 1933
• Sturtevant → First genetic map, 1913

5 Lines That Win Marks

1. Phenotypic ratio ≠ genotypic ratio in complete dominance (3:1 ≠ 1:2:1)
2. Law of Independent Assortment does NOT apply to linked genes
3. Incomplete dominance: F2 phenotypic = genotypic = 1:2:1
4. ABO: AB parents ($I^A$ $I^B$ × $I^A$ $I^B$) CANNOT produce O (ii) offspring
5. Recombination frequency max = 50% (> 50% is impossible)