Variation and Evolution

• Variation is the differences in the characteristics of individuals in a population.
• The three main causes of variation are the alleles that individuals have inherited, which are genetic causes.
• Examples of genetic variation include hair color and eye color, with red hair, blond hair, and dark hair being genetic, and blue eyes and brown eyes also being genetic.
• Some variations are caused by the environment, for example, the color of these flowers depends on the pH of the soil.
• Language in humans is another example of variation caused by the environment.
• Some variation is caused by a combination of genes and the environment, for example, height in humans, where some people have alleles which make them likely to grow taller, but their diet must also include enough calcium for their bones to fully develop.
• In any population of a species, there is a massive amount of genetic variation, which is due to mutations.
• Mutations are random changes to DNA, and most mutations have no effect on the phenotype.
• Some mutations can influence the phenotype, for example, alleles for tallness may lead to tallness as a person's diet is suitable.
• Very rarely, a mutation can lead to a new phenotype, and if the environment changes, this can lead to a rapid change in the species.
• In the 1950s, a virus was heading to the UK, and a mutation occurred which made the surviving rabbits resistant to the virus, giving the rabbit a new phenotype.
• The beneficial phenotype of this mutation is widespread in the UK rabbit population.
• Evolution is the change in the inherited characteristics of a population over time through a process of natural selection.
• The earth is teeming with living organisms, including large animals such as mammals and fish, smaller animals like insects, and plants such as ferns and trees.
• There are nearly 9 million different species of animals and plants on earth, and that number does not include microbes such as bacteria.
• Scientists believe that life first developed on earth more than 3 billion years ago, with the first life-forms being very simple, such as single cells.
• All species of living things have evolved from these simple life forms, a process scientists call evolution by natural selection.
• There is a massive amount of genetic variation within a population of a species, for example, with rabbits.
• Rabbits with alleles for thicker fur are more likely to survive colder temperatures, and these beneficial alleles may be passed on to their offspring over many generations, leading to a change in the population of rabbits.
• Rabbits with better eyesight or hearing are more likely to survive and reproduce, and these beneficial alleles may be passed on to their offspring over many generations, leading to a change in the population of rabbits.
• Sometimes two populations of one species can't become so different in phenotype that they can no longer interbreed to produce fertile offspring, and these two populations have now become two separate species, as seen with rabbits.
• Selective breeding, also known as artificial selection, is a process used to improve the desirable traits of an organism and eliminate the undesirable traits.
• The impact of selective breeding on food plants and domesticated animals has been significant.
• Selective breeding has produced dogs that are gentle natured.
• Domestic dogs have been selectively bred to have a gentle nature.
• Food crops such as wheat have been selectively bred to be resistant to disease.
• Animals such as cows have been selectively bred to produce more meat or milk.
• Certain plants have been selectively bred to produce large or unusual flowers.
• Selective breeding is carried out in stages: a mixed population of cows is taken, the largest male and female are selected, these are bred together, and the offspring are selected and bred together.
• The process of selective breeding can result in inbreeding, which can cause some breeds to be prone to disease or inherited defects.
• Dog breeds have been selectively bred for hundreds of generations and many dog breeds develop inherited disorders such as joint problems, heart disease, or epilepsy.
• Genetic engineering is the modification of an organism's genome using genes from another organism.
• Genetic engineering is used in medicine and agriculture.
• In genetic engineering, genes from one organism are cut out and transferred to cells of a different organism.
• The genome of the bacteria is modified to include a human gene.
• Insulin, a hormone involved in blood glucose regulation in humans, is produced by bacteria that have been genetically modified to contain the human insulin gene.
• Genetically modified or GM crops are plants that have been modified to produce a greater yield, be resistant to disease or insect attack, or produce bigger or better foods.
• Some GM crops are resistant to herbicides, allowing farmers to spray their fields to kill weeds without harming the GM crop.
• Genetic modification is currently being explored as a way to treat inherited disorders in humans, a process scientists call gene therapy.
• The long-term effects of gene therapy are not known, for example, if we modify a gene, we don't know the potential effects on other genes.