Evolution

• A gene is a section of DNA that codes to make a particular protein.
• In plant and animal cells, all chromosomes come in pairs. Each chromosome contains the exact same type of genes (ex. eye colour, hair colour) but they may be a different variation of that gene.
• Different variations of the same gene are referred to as alleles
• Some alleles are dominant while others are recessive.
• Genotype: the particular combination of alleles an organism possesses. (ex. TT/Tt/tt)
• Phenotype: the outward (physical) appearance of an organism (caused by their genotype) (ex. Tall/short)
• The genetic code refers to the manner in which cells store information. The information holds the blue prints for running all the chemical reactions in the body and therefore determines all the traits. The material that contains the code is DNA.
• DNA is made up of many repeating molecules known as nucleotides.
• DNA Nucleotides are made of: 1. phosphate group 2. 5 carbon sugar (deoxyribose) 3. nitrogenous bases (Adenine, Guanine, Cytosine, Thymine)
• Adenine and Guanine = Purine
• Cytosine, Thymine (DNA only), and Uracil (RNA only) = pyrimidine
• Deoxyribose sugar is found only in DNA. It differs from ribose sugar, found in RNA, by the lack of a single oxygen atom.
• Phosphate: Links neighbouring sugars together.
• Sugar: one of two types possible: ribose in RNA and deoxyribose in DNA
• Base: One of the four types possible. This part of the nucleotide comprises the coded genetic message.
• When many nucleotides attach together it looks like a twisted ladder. The sugar and phosphate make up the sides of the ladder and the bases each other join across the middle forming the steps of the ladder.
• DNA is often referred to as a double helix structure because it has two rows of nucleotides forming a corkscrew shape.
• Nucleotides join together in a predictable way referred to as the base pairing rule. Only the correct pairing of bases will form hydrogen bonds and hold together.
• 2 hydrogen bonds hold adenine to thymine
• 3 bonds attach cytosine to guanine
• RNA (ribonucleic acid) is a molecule that is very similar to DNA. Instead of storing genetic information, its function is to act as a messanger between DNA and the cell’s ribosomes in order to make proteins needed by the cell.
• DNA has two backbones, has deoxyribose sugar, and is trapped in the nucleus
• RNA has one backbone, has no thymine, has ribose sugar, and can move out of the nucleus
• Covalent bonds hold the backbones together
• Evolution is a change in a population over time.
• A population is all the members of a single species occupying a particular area at the same time (ex. all foxes in Yellowstone, all cedar trees in a mountain range)
• The total of all of the genes of all the individuals in a population makes up the gene pool.
• The gene pool of a population will remain stable (unchanged) so long as: no mutations, population is very large, no individuals enter/leave, random mating, environment stays the same.
• Mutations: Mutations to an organisms DNA happen naturally all the time but at a very low rate. It can happen that an entirely new allele for a particular trait is formed.
• Gene flow: immigration (movement of alleles into a population), emigration (movement of alleles out of a population)
• Genetic drift: the phenomenon by which the allele appearances in a population changes from generation to generation due to random events or chance. This depends on the size of the population. (Small populations are more vulnerable because of the fewer alleles)
• Non-random mating/sexual selection: Selecting a mate based on a certain phenotype (very powerful). (ex. male peacocks vs female peacocks)
• Adaptation: any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment.
• Fitness: how well an organism can survive and reproduce in its environment.
• Populations are kept in check by predators, diseases, limitations in food, water, and other resources that are essential for survival, hence there is a ”struggle for existence”
• Natural Selection was proposed by Charles Darwin and Alfred Russell Wallace.
• Some variations are more suitable for environmental conditions.
• Fitness of individuals: Some individuals have genetic variations that create more favourable traits in a particular environment or habitat. These favourable traits may allow an individual to live longer and produce more offspring.
• Natural selection: the organisms best suited for the environment will survive. The best suited individuals will live longer and leave more offspring. Their offspring will inherit advantageous genotypes and phenotypes and will also be fit for their environment.
• Organisms with less favourable traits are less likely to survive and reproduce. Over time, these genes may be “wiped out” of a population.