Learning question: What factors affect evolution? Title: The roles of genes and environment in evolution 12th February 2014 Learning question: What factors affect evolution? Homework: Module test next week – study this unit Starter: what do these two organisms have in common?

Key words Genetic drift Selection pressure Stabilising selection Directional selection Evolutionary force Environmental resistance Isolating mechanisms

Learning Outcomes Explain, with examples, how environmental factors can act as stabilising or evolutionary forces of natural selection. Explain how genetic drift can cause large changes in small populations.

Variation and Natural Selection The set of alleles in a population is it’s gene pool Each individual can have any combination of alleles in the gene pool producing variation Some individuals more likely to survive They reproduce and pass genes on to offspring Advantageous alleles become more frequent in the population

Environmental Resistance Environmental factors that limit the growth of a population offer environmental resistance These factors can be biotic (living factors) or abiotic (non-living factors)

Selection pressures An environmental factor that “selects” for some members of a population over others Offers an advantage onto certain individuals

Discuss! Explain to your neighbour what environmental resistance and selection pressures are. If the person speaking is incorrect, the partner must explain the correct term and give an example.

Stabilising Selection If the environment stays stable The same alleles will be selected for in successive generations Nothing changes, this is called stabilising selection

Stabilising Selection

Stabilising Selection

Directional Selection Change in the environment resulting in a change in the selection pressures on the population Previously disadvantageous alleles maybe selected for Change in the genetically determined characteristics of subsequent generations of the species A.k.a. evolution

Directional Selection

Directional Selection

Discuss! Explain to your neighbour what stabilising selection and directional selection are. If the person speaking is incorrect, the partner must explain the correct term and give an example.

Genetic Drift A change in the gene pool and characteristics within the population. This change has occurred by chance rather than as the result of natural selection.

Genetic Drift and Islands Genetic drift is thought to happen relatively frequently in populations on islands. Small populations Geographically separated from other members of their species Evidence Many isolated islands have their own endemic species of plants and animals

Genetic Drift Reduces genetic variation Reduce the ability of the population to survive in a new environment May contribute to the extinction of a population or species Could lead to the production of a new species

Genetic Drift – Frog Hoppers The colours of the common frog-hopper are determined by seven different alleles of a single gene. The range of colours and their frequencies, on different islands in the Isles of Scilly, are very variable, There are different selection pressures on the different islands

Genetic Drift – Frog Hoppers

The answers

Your task Complete questions 1-4 from page 141 of your textbook. Correct your work using the mark scheme at the back of the book.

Natural selection video