Adaptations, Natural Selection & Evolution

1. Mutations MUTATION = change in structure or composition of an organism’s DNA MUTANT = an organism that displays the genotypic mutation in its phenotype

Mutations are random events that tend to be recessive so appear in a low number of the population Mutations are the source of new variation Variation is the differences between members of a species Mutagenic agents that can increase mutation rates There are 2 main categories of mutagenic agents: Chemicals & Radiation Chemical Mutagenic Agents: -Mustard Gas -Colchicine -Caffeine -Formaldehyde Radiation Mutagenic Agents: -X-rays -UV Light -Gamma Rays

Mutations can be: Advantageous for the organism- the mutation has caused the mutant to be better than the original organism. It is the source of new variation. E.g. polyploidy in plants Disadvantageous for the organism- the mutation causes harm to the organism E.g. cystic fibrosis/sickle cell anaemia Neutral- the mutation causes no change to the organism, it is neither beneficial or harmful

An adaptation is a characteristic possessed by an organism which makes it well suited to its environment Adaptations are favoured by natural selection as they increase the individual’s chance of survival Adaptations can be: Structural Physiological Behavioural 2. Adaptations

The Galapagos Islands lie west of South America in the Pacific Ocean On these islands live 13 different species of Finch In order to survive, each Finch species has adapted to occupy a particular niche (role) 2. Adaptations

Different Finch species have: different beak shapes and sizes different habitats/niche Can you think which finch lives near bark containing burrowing insects? Which lives on the ground near trees that produce thick walled seeds? 2. Adaptations

Bee pollinated plants Bee pollinated flowers often have UV colouring, invisible to the human eye but visible to the bee. To the bee this is a target signalling where the nectar is, and promotes pollination.

Cacti Succulent tissue, deep root and superficial roots, no broad leaves.

Polar bear Camouflaged, dark skin for insulation, blubber, wide feet.

African Bullfrog Uses spade-like hind-legs to burrow away from predators.

Sea dragon Camouflaged to protect from predators.

Camel

Elephant

Charles Darwin 3. Natural selection What examples of variation can you think of in humans? Can you think of other examples of variation in other species? An organism that is ‘struggling for survival’ means that only the best adapted organisms will survive to pass on their genes Organisms that are best adapted are said to have a ‘selective advantage’ over other members of the species

Sexual reproduction produces more offspring than environment can support Inherited variation is expressed in phenotypes Healthiest, strongest, fastest etc survive & breed Some slower rabbits are caught Some weaker rabbits die More offspring produced than the environment can support, best adapted survive to pass on genes Poorly adapted die

Natural selection in action: The Peppered Moth Peppered moth exists in 2 colours, light and melanic. Each have selective advantage in different environments.

light moths had a selective advantage well camouflaged against the lichen-covered trees, they were better able to avoid predation During the 19th century pollution killed off some of the lichens and soot deposits caused the tree bark to appear darker Light moths = no longer camouflaged and more likely to be eaten by birds Light is favoured Before the industrial revolution:

Dark moths had a greater chance of reproducing and passing on the alleles that made them dark caused a gradual increase in the proportion of dark moths until light moths became very rare in industrial areas The moth populations in these areas had evolved This change from predominantly light to dark forms in industrial areas is called industrial melanism Melanic is favoured Note that this change was not due to pollution making the moths darker. The dark variety had always existed in small numbers, but only had a selective advantage when the selection pressure changed.

Resistance to antibiotics a. One mutant bacteria arrives spontaneously in the population. b. Mutant bacteria has selective advantage and survives. c. Resistant bacteria reproduces to make more resistant bacteria.

Resistance to antibiotics d. One of these bacteria may be resistant to a 2 nd antibiotic. e. Mutant bacteria has selective advantage and survives to reproduce more like bacteria.

A species is a group of organisms that can interbreed to produce fertile offspring All of the members of the same species make up a population the gene pool refers to the different genes within an interbreeding population Speciation is the name given to the process where two new species are formed from one original species 4. Speciation

Speciation requires some sort of isolation barrier (something that causes the original population to become divided) These barriers can be: Geographical (seas, rivers, mountains/deserts) Ecological (temperature, water availability, pH) Reproductive (sex cells unable to fuse, unsuccessful mating displays, flowering at different times of year

Population separated by an isolation barrier Different mutations occur in each new sub-population Variation is displayed in each new population & natural selection occurs where those with the selective advantage will survive & pass on their genes After many generations, mutations and natural selection changing the gene pool of each population, even if the isolation barrier is removed, these sub-groups will no longer be able to interbreed to produce fertile offspring