IP Biology Upper Sec 14: Inheritance

These notes align with SEAB GCE O-Level Biology (6093) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

What you must know

• Gene is a DNA segment; allele is an alternative form. Dominant masks recessive; codominant both expressed. Homozygous = same alleles; heterozygous = different alleles. Phenotype = observable traits; genotype = allele pair.
• Monohybrid crosses: use Punnett squares; F2 ratio 3:1 for heterozygous cross; test cross gives 1:1 if heterozygous. Deviations from chance due to small sample or linkage (beyond syllabus detail).
• ABO blood group: multiple alleles ($I^A, I^B, I^O$); $I^A$