Overview
This lecture covers inheritance, variation, and evolution in GCSE Biology, focusing on reproduction, DNA structure, genetic inheritance, evolution, selective breeding, genetic engineering, and classification.
Types of Reproduction
- Sexual reproduction involves fusion of male and female gametes, leading to varied offspring (meiosis).
- Asexual reproduction involves one parent, no gametes, and produces identical offspring (mitosis).
- Some organisms can reproduce both sexually and asexually depending on conditions.
Meiosis and Genetic Variation
- Meiosis halves the chromosome number in gametes; fertilization restores it to normal.
- Meiosis produces four genetically different gametes; mitosis increases cell number in the embryo.
- Mutations and sexual reproduction generate genetic variation for natural selection.
Advantages & Disadvantages of Reproduction
- Sexual reproduction: creates variation and survival advantage if environment changes, can be used by humans for selective breeding.
- Asexual reproduction: one parent, more efficient, faster, produces many identical offspring in favorable conditions.
DNA, Genes, and the Genome
- DNA is a double helix polymer made of nucleotides (A, C, G, T bases).
- A gene is a DNA segment coding for a specific protein; a genome is an organism’s entire genetic material.
- Understanding the genome helps identify disease genes, treat inherited disorders, and trace migration.
Genetic Inheritance
- Key terms: gene, allele, dominant, recessive, homozygous, heterozygous, genotype, phenotype.
- Dominant alleles always show; recessive alleles show only if two are present.
- Punnett squares and ratios predict genetic cross outcomes.
Inherited Disorders & Sex Determination
- Polydactyly (dominant allele), cystic fibrosis (recessive allele) are inherited disorders.
- Human body cells have 23 chromosome pairs; XX (female), XY (male) determines sex.
Variation and Evolution
- Variation comes from genes, environment, or both; mutations introduce new traits.
- Evolution is the change in inherited traits over time via natural selection.
- Speciation occurs if populations can't interbreed to produce fertile offspring.
Selective Breeding, Genetic Engineering, and Cloning
- Selective breeding enhances traits in plants/animals but can cause inbreeding problems.
- Genetic engineering introduces genes from one organism to another for desired traits (e.g., disease resistance).
- Cloning produces identical organisms via tissue culture, cuttings, embryo transplants, or adult cell cloning.
Development of Genetics and Evidence for Evolution
- Darwin and Wallace proposed evolution by natural selection; Mendel’s genetic discoveries were later recognized.
- Fossils and antibiotic resistance in bacteria support evolution.
- Extinction is the loss of all individuals of a species; bacteria can rapidly evolve resistance.
Classification of Living Organisms
- Linnaeus classified life into a hierarchy using binomial names.
- Modern classification includes the three-domain system: Archaea, Bacteria, Eukaryota.
- Evolutionary trees show relationships among organisms based on current and fossil data.
Key Terms & Definitions
- Meiosis — Cell division producing gametes with half the chromosome number.
- Mitosis — Cell division resulting in identical cells.
- Allele — Different forms of a gene.
- Genotype — Genetic makeup of an organism.
- Phenotype — Observable characteristics of an organism.
- Mutation — Change in DNA sequence, introducing variation.
- Genome — Complete set of genetic material in an organism.
- Selective breeding — Human-directed breeding for desired traits.
- Genetic engineering — Altering an organism's genome using genes from another organism.
- Cloning — Making genetically identical copies of organisms.
- Speciation — Formation of new species when populations become reproductively isolated.
Action Items / Next Steps
- Review Punnett square techniques for predicting genetic crosses.
- Practice interpreting evolutionary trees and family trees.
- Read more about the ethical issues in genetic engineering and cloning.
- Study the three-domain classification system and examples of each group.