17.4 Monohybrid inheritance

The vocabulary and prediction of single-gene inheritance. Genotype (alleles present) vs phenotype (observable feature). Homozygous (two same alleles, pure-breeding) vs heterozygous (two different alleles). Dominant alleles expressed when present; recessive only when no dominant. Punnett squares predict offspring genotype + phenotypic ratios — Cambridge core ratios 1:1 (Bb × bb) and 3:1 (Bb × Bb). Pedigree diagram conventions (squares = males, circles = females, filled = affected). HL extensions: test cross to identify unknown dominant genotype; codominance with ABO blood groups (alleles I^A, I^B, I^O — I^A and I^B codominant); sex linkage (gene on X chromosome) explaining why traits like red-green colour blindness are more common in males than females.