Evolution & Natural Selection
Evolution is a change in the inherited characteristics of a population over generations through natural selection. Genetic variation arises from random mutations, and individuals with phenotypes best suited to their environment are more likely to survive, reproduce, and pass on their advantageous alleles.
- Evolution
- The gradual change in inherited traits of a population over many generations.
- Natural selection
- Survival of the fittest; organisms best suited to the environment survive and reproduce.
- Mutation
- A random change in DNA which can create new alleles.
Mitosis (2n → 2n) vs Meiosis (2n → n) & Ribosome Protein Synthesis
1. Interphase (DNA Replication)
Diploid parent cell (2n = 46 in humans). DNA replicates so each chromosome consists of two identical sister chromatids; subcellular organelles (mitochondria, ribosomes) also double.
Diploid germ cell (2n = 46). DNA replicates once to form homologous pairs of doubled chromosomes ready for two rounds of division.
Key Concepts & Exam Definitions (6)
- Evolution
- The gradual change in inherited traits of a population over many generations.
- Natural selection
- Survival of the fittest; organisms best suited to the environment survive and reproduce.
- Mutation
- A random change in DNA which can create new alleles.
- Speciation
- The formation of a new and distinct species in the course of evolution.
- Extinction
- When there are no remaining individuals of a species still alive.
- Selective breeding
- The process where humans breed plants and animals for particular genetic characteristics.
Quick-Fire Flashcards (5)
Click any card to check the answer, then mark it as Known to track your progress.
What drives natural selection?
What is a mutation?
Why are fossils important for the theory of evolution?
What causes a species to become extinct?
What is speciation?
Exam-Style Questions & Mark Schemes (3)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Explain how bacteria can become resistant to antibiotics.
Click “Check Mark Scheme” to compare your answer, A random mutation may give a bacterium resistance to an antibiotic. When treated, non-resistant bacteria die, but the resistant one survives and reproduces, passing on the resistance allele. Over time, the entire population becomes resistant.
- Q2
Outline Charles Darwin's theory of natural selection.
Click “Check Mark Scheme” to compare your answer, Individuals in a species show variation. Those with characteristics best suited to the environment are more likely to survive and reproduce. They pass these beneficial alleles to their offspring.
- Q3
Compare selective breeding and natural selection.
Click “Check Mark Scheme” to compare your answer, In selective breeding, humans choose which organisms reproduce based on desired traits. In natural selection, the environment determines which organisms survive and reproduce based on their fitness.
Common Exam Questions (4)
What is natural selection?
Natural selection is the process by which organisms with alleles better adapted to their environment are more likely to survive and reproduce, passing those advantageous alleles to their offspring so they become more common in the population over generations.
Who proposed the theory of evolution by natural selection?
Charles Darwin proposed the theory of evolution by natural selection in his 1859 book On the Origin of Species, following his observations on the Galapagos Islands.
What causes variation in a population?
Genetic variation within a population is caused by random mutations in DNA and by the sexual reproduction shuffling of alleles during meiosis and fertilisation.
What are fossils?
Fossils are the preserved remains, mineralised casts, or traces of organisms that lived thousands or millions of years ago, preserved in rocks, ice, or amber, providing evidence for how species have changed over geological time.
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Related study guides
DNA, Genes & Inheritance
DNA (deoxyribonucleic acid) stores the genetic instructions needed for an organism to grow, develop, and reproduce. Packaged into chromosomes inside the cell nucleus, genes code for specific proteins, while inherited combinations of alleles determine an organism's genotype and observable characteristics (phenotype).
Ecosystems, Food Chains & Webs
An ecosystem is the interaction of a community of living organisms (biotic factors) with the non-living parts of their environment (abiotic factors). Energy enters ecosystems via photosynthetic producers and flows through trophic levels in food chains, while decomposers recycle carbon, water, and mineral ions.