Flashcards · 0610 · Topic 18

Variation and selection flashcards

18 cards on Topic 18, subtopics 18.1 to 18.3. Pick a subtopic or study them all.

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Variation: Differences between individuals of the same species.
Continuous vs discontinuous variation: Continuous: a range of phenotypes between two extremes, e.g. body length and mass; caused by genes and environment. Discontinuous: a limited number of phenotypes with no intermediates, e.g. ABO blood group; usually genes only.
Graphs for continuous and discontinuous variation: Continuous: histogram with touching bars and equal class intervals. Discontinuous: bar chart with separate bars.
Mutation v cause of mutation: Radiation and chemicals increase the rate; mutation also happens without them.
Mutation (Core) and what it produces: Mutation is genetic change. It is how new alleles are formed. Ionising radiation and some chemicals increase the rate.
Gene mutationExtended: A random change in the base sequence of DNA.
Four sources of genetic variation in populationsExtended: Mutation, meiosis, random mating and random fertilisation.

Adaptive feature: An inherited feature that helps an organism to survive and reproduce in its environment.
How to answer an "adaptive feature" question about a species: For each feature say what it does and how that helps survival or reproduction in that environment. The feature must be inherited, not gained during life.
Adaptation (Extended definition)Extended: The process, resulting from natural selection, by which populations become more suited to their environment over many generations.
Adaptive features of xerophytesExtended: Thick waxy cuticle, sunken stomata, hairs, rolled leaves, few stomata, spines instead of leaves, deep or wide roots, water-storage tissue.
How do sunken stomata, hairs and rolled leaves reduce water loss?Extended: They trap moist air next to the stomata, so the water vapour concentration gradient is smaller and less water vapour diffuses out.
Adaptive features of hydrophytesExtended: Large air spaces (buoyancy); stomata on the upper surface of floating leaves; thin or no cuticle; little xylem and support tissue; large flat leaves.

Natural selection, in steps: Variation within the population → many offspring → struggle for survival (competition, predation, disease) → better-adapted individuals survive and reproduce more → they pass on their alleles → over many generations the allele becomes more common.
Individual v population (in selection): Individuals do not adapt during their lifetime; populations change over generations.
Selective breeding, in steps: Select individuals with the desired feature → cross them → select offspring showing the feature → breed from them → repeat over many generations.
How antibiotic resistance develops in bacteriaExtended: A random mutation gives a few bacteria resistance → the antibiotic kills non-resistant bacteria → resistant ones survive and reproduce, passing on the allele → over many generations a resistant strain develops.
Natural selection vs artificial selectionExtended: Natural: the environment selects; features that aid survival; usually slower. Artificial: humans select; features useful to humans; usually faster.