Edexcel A Level Biology Revision Guide: Genetics and Inheritance

Genetics and inheritance is a core topic in Edexcel A Level Biology. This comprehensive revision guide covers DNA structure, genes, inheritance patterns, genetic variation, and genetic engineering, providing everything you need to excel in this challenging topic.

DNA Structure and Function

DNA Structure

• Double helix model (Watson and Crick)
• Made of nucleotides
• Each nucleotide: sugar, phosphate, base
• Bases: A, T, G, C (A pairs with T, G pairs with C)

DNA Replication

• Semi-conservative process
• Unwinding of double helix
• Base pairing
• Formation of two identical molecules

Genes and Chromosomes

• Gene: section of DNA coding for protein
• Chromosome: long DNA molecule with many genes
• Alleles: different forms of same gene
• Locus: position of gene on chromosome

Inheritance Patterns

Mendelian Inheritance

• Dominant and recessive alleles
• Homozygous and heterozygous
• Genotype and phenotype
• Monohybrid crosses

Dihybrid Inheritance

• Two genes inherited independently
• 9:3:3:1 ratio in F2 generation
• Independent assortment
• Linked genes exception

Sex Linkage

• Genes on X or Y chromosomes
• X-linked disorders
• Inheritance patterns
• Examples: hemophilia, color blindness

Codominance and Multiple Alleles

• Both alleles expressed
• Blood groups example
• Incomplete dominance
• Multiple allele systems

Genetic Variation

Sources of Variation

• Mutation: changes in DNA
• Meiosis: independent assortment, crossing over
• Random fertilization
• Environmental factors

Mutations

• Gene mutations: point mutations, frameshift
• Chromosome mutations: deletion, duplication, inversion, translocation
• Causes: radiation, chemicals, errors in replication
• Effects: harmful, beneficial, neutral

Genetic Engineering

Recombinant DNA Technology

• Cutting DNA with restriction enzymes
• Joining DNA with ligase
• Inserting into vectors
• Cloning and expression

Applications

• Insulin production
• Gene therapy
• Genetically modified crops
• DNA fingerprinting

Exam Tips

1. Understand Inheritance

• Practice genetic crosses
• Use Punnett squares
• Understand ratios
• Apply to new situations

2. Know DNA Structure

• Draw DNA structure
• Understand base pairing
• Know replication process
• Link structure to function

3. Practice Calculations

• Genetic cross problems
• Probability calculations
• Chi-squared tests
• Show working clearly

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Use this revision guide as part of your comprehensive exam preparation. Combine with past paper practice and expert tutoring for best results.