3U Evolution Notes. Natural Selection: What is Evolution? -The idea that gene distribution changes over time -A change in the frequency of an allele

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1 3U Evolution Notes What is Evolution? -The idea that gene distribution changes over time -A change in the frequency of an allele Let s look back to what we know: From genetics we can say that a gene is A unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring. An allele is One of two or more alternative form of a gene that arise by mutation and are found at the same place on a chromosome. So genes determine characteristics of offspring, and these genes are caused by having specific alleles. The change of the frequency of these alleles (resulting in changes in gene distribution) is evolution in its most basic form. There are factors that affect Allele Frequencies. These factors are essentially the mechanisms of evolution: -Natural Selection -Non-Random Mating -Sexual Selection -Mutations - Gene Flow -Genetic Drift -*Artificial Selection Natural Selection: The process whereby organisms better adapted to their environment tend to survive and produce more offspring. Those with a high fitness survive, survival of the fittest so to speak The theory of its action was first explained by Charles Darwin and is now believed to be the main process that brings about evolution. Think back to the Bean Hunter lab, where the group members with the best suited tool or utensil for collecting beans was the most likely to survive to the next generation. They then pass on their genes and make offspring with the same tool that they had. Conversely the group members who were not well adapted (think knives) died out and were unable to pass on their genes. This is natural selection and forms the basis of the theory of evolution. `

2 3 Types of Selection: Directional, Stabilizing, Disruptive Directional Selection: -A single phenotype is favoured -Causes allele frequency to continuously shift in one direction Ex. Brown bugs vs Green If there is a gene that makes something a particular colour (moths for example) and one trait is better than the other (black moths on the trees blend in, white ones are spotted easily and eaten). The moths with the preferred trait (black) are more likely to survive and reproduce, thereby passing on its genes to be black *This is a population distribution graph. It shows how many individuals in a population that have a particular trait. Stabilizing Selection: -Favours average individuals (intermediate phenotypes) -Reduces variation -Improves adaptation when environment conditions are stable Ex. Human Birth Weight Babies born when they re too small are called premature and have a high risk of mortality, babies too large and heavy can cause problems with delivery. Therefore babies with average birth weights are most likely to survive and pass on the genes that would lead to an average birth weight.

3 Disruptive Selection: -Favours extreme individuals (extreme phenotypes) -May actually eliminate intermediate phenotypes -Can lead to speciation Ex. Bunnies with Black, Grey, and White fur In an area where there are white rocks and black rocks there are bunnies that have adapted fur to match the colour of the rocks in order to blend in. Those with black fur or white fur blend in and survive. If a black and white fur bunny breed and have a grey fur bunny, they are less likely to be able to survive being eaten by predators. This is due to being more noticeable/not being able to blend in to either rock colour. This means they are less fit and less likely to pass on their genes that produce grey fur. There will be less members of the population with alleles that make them grey. Non-Random Mating Individuals in a population select mates, often on the basis of their phenotypes -Increases proportion of homozygous individuals

4 Sexual Selection: Preference by one sex for certain characteristics in individuals of the other sex. Many animals look for specific traits in a mate (especially humans). An example of this would be that Caribou females prefer more dominant males. Mutations: A gene mutation is a permanent alteration in the DNA sequence that makes up a gene. An organism s DNA affects how it looks, how it behaves, and its physiology. A change in an organism s DNA can cause changes in all aspects of its life. Mutations can range in size; they can affect anywhere from a single DNA building block (base pair) to a large segment of a chromosome that includes multiple genes. Sickle Cell Anemia is the result of a point mutation, which changes just one nucleotide in the gene for hemoglobin. This mutation causes the hemoglobin in red blood cells to distort to a sickle shape when deoxygenated. Blue eyes are another example of a mutation. Another example is mutations in regulatory genes changing the shapes of insect hindwings.

5 Gene Flow: Transfer of alleles from one population to another. Occurs between 2 different interbreeding populations with different allele frequencies. Migration into or out of a population affects the proportion of members carrying a particular variant of a gene. This may change allele frequencies in either or both populations. Ex. 4 birds from Population A immigrate to Population B, which has no dominant alleles for a certain trait. Through mating it incorporates its alleles into Population B Genetic Drift: Disappearance of certain genes from when individuals die or do not reproduce. There are changes in allele frequency within a small population. This change is more sudden and drastic in a smaller population because it s a smaller sample size (think of flipping a coin 10x vs 1000x). A greater proportion of the individuals will have changed rather than if that small change in allele frequency occurred in a larger group. This can be caused by environmental events such as an Earthquake, Flood, Disease. This results in a sharp reduction in the size of a population and the survivors often have a fraction of the alleles that were present before the event. This means a less diverse Gene Pool. When this happens it is called the Bottleneck Effect. This can also be caused by a few individuals from a large population leave to establish a new population. This is called the Founder Effect and results in reduced genetic diversity.

6 Artificial Selection: The breeding of plants and animals by humans to produce desirable traits. Dogs were selectively/artificially bred to produce different traits. Dogs were domesticated from wolves, meaning that over time humans specifically bred wolves together that were less aggressive and eventually each generation became less aggressive and started to differ in appearance as well. These physical traits were then specifically bred for and after a long long period of time dogs were the result of selectively breeding wolves by humans.

7 Animals with Adaptations vs Variations Adaptation: A change in which an organism or species becomes better suited to its environment -Helps an organism survive & reproduce -Can be structural, behavioural, or a physiological process They are gradual and accumulate the changes over many generations. They are caused by random, heritable mutations in DNA. Variation: Difference between individual organisms from genetic differences or by environmental factors. -Can lead to an adaptation if the trait is positively selected for. Examples of adaptations: 1. Structural -Owl (talons/eyesight) -Sharks (sensory organs, teeth, graceful swimmers) -Bats (Sonar) -Humans (brain, bipedal, thumbs) -Stick Insect (Camouflage) Mimicry- Special structural adaptation. A harmless creature poses as a harmful species in either colour or structure. Predators believe the organism is either dangerous or untasty. -Viceroy Butterfly, King Snake 2. Behavioural Things that animals do, not what they have - Migration (Canada Geese) -Birds (bird calls) - Meerkats (standing) 3. Physiological -Bears (Hibernation) -Squirrels (Hibernation) Examples of Variation: -Cats (different fur colour) -Birds (colour of feathers) -Animals (height) -Plants (# of leaves) -Plants (size of fruit) -Animals (weight)