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Biology · Quick Reference
Lesson 13 — Mendelian Genetics Cheat Sheet
In one line: Aa × Aa gives 3:1; two gene pairs give 9:3:3:1 — and blood type AB shows what codominance really looks like.
Key Ideas
1Segregation. Alleles separate during gamete formation.
2Independent assortment. Genes on different chromosomes sort independently.
3Monohybrid (Aa×Aa). 1:2:1 genotype, 3:1 phenotype.
4Dihybrid. 9:3:3:1 phenotype ratio.
5Incomplete dominance blends (pink); codominance shows both fully (AB).
Blood Groups
IAIA or IAi
Type A
IBIB or IBi
Type B
IAIB
Type AB (codominant)
ii
Type O