Genetics and Heredity

Where this fits in the syllabus

Grade 11 · Term 3

Key points to revise

Revise Genetics and Heredity fast with concise, exam-ready key points

About O/L Science: O/L Science integrates physics, chemistry, and biology into a single subject across Grade 10 and 11.

• DNA: double helix; base pairs A-T, G-C; carries genetic instructions
• Gene: section of DNA coding for a protein (e.g. enzyme, structural protein)
• Alleles: different versions of a gene; dominant (T) masks recessive (t)
• Genotype: actual allele combination (TT, Tt, tt); Phenotype: observable characteristic
• Inheritance patterns: monohybrid cross → 3:1 ratio (dominant : recessive)

Must know

• Homozygous: same alleles (TT or tt); Heterozygous: different (Tt)
• Monohybrid cross Aa × Aa → 1 AA : 2 Aa : 1 aa (3:1 phenotype ratio)
• Sex determination: XX = female; XY = male; sex chromosomes from father
• X-linked recessive: colour blindness, haemophilia — more common in males
• Mendel's Laws: Segregation + Independent Assortment

Source: NIE O/L Science Grade 11 — Unit 5: Genetics

In the Syllabus