DNA, Genes and Principles of Heredity — O/L Science

What must I remember about DNA, Genes and Principles of Heredity?

• 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)

Test yourself (1 minute)

1. Homozygous

   same alleles (TT or tt); Heterozygous: different (Tt)

2. Monohybrid cross Aa × Aa → 1 AA

   2 Aa : 1 aa (3:1 phenotype ratio)

3. Sex determination

   XX = female; XY = male; sex chromosomes from father

Practise DNA, Genes and Principles of Heredity questions today

Must know

• X-linked recessive: colour blindness, haemophilia — more common in males
• Mendel's Laws: Segregation + Independent Assortment

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

Where does DNA, Genes and Principles of Heredity fit in the syllabus?

Grade 11 · Term 3