01Mendel's laws
Law of segregation: each organism has two alleles per gene, which separate into different gametes. Law of independent assortment: alleles of different genes (on different chromosomes) are sorted independently.
Dominant alleles mask recessive ones. Genotype = allele combination (Aa); phenotype = observable trait.
02Crosses and probability
Monohybrid Aa × Aa → 3:1 phenotype, 1:2:1 genotype. Dihybrid AaBb × AaBb → 9:3:3:1. A testcross with a homozygous recessive reveals an unknown genotype.
Rules of probability: multiply for 'and' (independent events), add for 'or' (mutually exclusive).
03Pedigrees and chi-square
Autosomal recessive traits skip generations; autosomal dominant traits appear in every generation with affected parents.
Chi-square: χ² = Σ (o − e)² / e. Compare to the critical value (df = categories − 1; p = 0.05). If χ² exceeds it, reject the null hypothesis.
04Notebook box
Worked example: AaBbCc × AaBbCc. Probability of aabbcc? → (1/4)(1/4)(1/4) = 1/64.
Critical values (p = 0.05): df 1 = 3.84, df 2 = 5.99, df 3 = 7.81.