Topic 6: Inheritance, Variation and Evolution

Introduction

• Content in bold is for higher tier only.
• Applies to both separate science and double award students.
• Licensed under CC BY-NC-ND 4.0 by PMT Education.

Reproduction (6.1)

Sexual and Asexual Reproduction (6.1.1)

• Meiosis: Formation of four non-identical cells from one cell.
• Mitosis: Formation of two identical cells from one cell.
• Sexual Reproduction:
  • Involves male and female gametes (sperm and egg in animals, pollen and egg in plants).
  • Gametes formed by meiosis; each has 23 chromosomes.
  • Fusion during fertilization mixes genetic information, producing variation.
• Asexual Reproduction:
  • Involves one parent, no gametes joining.
  • Uses mitosis to create clones, genetically identical.
  • Common in bacteria, some plants, and animals.

Meiosis (6.1.2)

• Formation of four non-identical gametes with one chromosome copy each.
• Chromosome shuffling leads to genetic diversity.
• Fertilization restores chromosome number to 46.
• Embryo formation through mitosis and differentiation.

Advantages and Disadvantages (6.1.3)

• Sexual Reproduction:
  • Variation in offspring; survival advantage in changing environments.
  • Allows selective breeding for desirable traits.
• Asexual Reproduction:
  • Faster, less energy required, only one parent needed.
  • Produces identical offspring, advantageous in stable environments.

DNA and the Genome (6.1.4)

• DNA: Polymer forming a double helix with bases forming complementary pairs (A-T, C-G).
• Genes: Sections of DNA coding for proteins.
• Human genome study aids understanding of diseases, treatments, and human migration.

DNA Structure (6.1.5 - Biology Only)

• DNA made of nucleotides (sugar, phosphate, base).
• Base pairing (A-T, C-G) forms genetic code.
• Non-coding DNA regulates gene expression.

Protein Synthesis

• Process of creating proteins from DNA code.
• Involves transcription (mRNA creation) and translation (protein assembly at ribosomes).
• Mutations can affect protein structure/function.

Genetic Inheritance (6.1.6)

• Key Terms:
  • Gamete: Reproductive cell with 23 chromosomes.
  • Chromosome: DNA structure in cell nucleus.
  • Gene: DNA segment coding for protein.
  • Alleles: Different gene forms; can be dominant or recessive.
  • Genotype: Allele combination.
  • Phenotype: Observable traits.
• Use of Punnett squares to predict inheritance patterns.

Inherited Disorders (6.1.7)

• Polydactyly: Dominant allele disorder causing extra digits.
• Cystic Fibrosis: Recessive allele disorder affecting cell membranes.
• Embryonic Screening: Genetic condition analysis with ethical, social, and economic implications.

Sex Determination (6.1.8)

• 23rd chromosome pair determines sex.
• Females: XX, Males: XY.
• Genetic probability of sex inheritance.

Variation and Evolution (6.2)

Variation (6.2.1)

• Phenotype influenced by genotype and environment.
• Genetic variation arises from DNA mutations.

Evolution (6.2.2)

• Evolution: Change in inherited traits over time via natural selection.
• Mutations providing survival advantages lead to species evolution.

Selective Breeding (6.2.3)

• Humans breed organisms for desired traits.
• Risks include inbreeding and reduced genetic diversity.

Genetic Engineering (6.2.4)

• Modifying an organism's genome to introduce desired traits.
• Applications in agriculture and medicine (e.g., GM crops, gene therapy).

Cloning (6.2.5 - Biology Only)

• Creating genetically identical organisms.
• Methods include tissue culture, cuttings, embryo transplants, and adult cell cloning.

Understanding Genetics and Evolution (6.3)

Theory of Evolution (6.3.1 - Biology Only)

• Proposed by Charles Darwin; supported by natural selection evidence.
• Controversies included conflict with religious views and lack of genetic understanding at the time.

Speciation (6.3.2 - Biology Only)

• New species development through allele selection and isolation.
• Alfred Russel Wallace contributed to the theory.

Understanding Genetics (6.3.3 - Biology Only)

• Gregor Mendel's experiments laid foundation for understanding inheritance.
• Chromosomes and genes linked with inheritance patterns.

Evidence for Evolution (6.3.4)

• Fossils and antibiotic resistance in bacteria are key evidence.

Fossils (6.3.5)

• Fossils show historical life forms and evolutionary changes.
• Limitations include absence of early soft-bodied organisms.

Extinction (6.3.6)

• Causes include environmental changes, new predators, diseases, competition, and catastrophic events.

Resistant Bacteria (6.3.7)

• Antibiotic resistance arises from mutation and selective pressure.
• Measures to slow resistance include careful antibiotic use and improved hygiene.

Classification of Living Organisms

• Linnaean System: Kingdoms, phylum, class, order, family, genus, species.
• Three-domain System: Archaea, Bacteria, Eukaryota.
• Evolutionary Trees: Used to show relationships based on classification and fossil data.

These notes are intended to serve as a detailed summary and study aid on the topic of Inheritance, Variation, and Evolution for the AQA Biology GCSE.