Genetic diversity Genetic diversity Genetic diversity – Genetic diversity Genetic diversity – the number of alleles in a species or population Genetic diversity Genetic diversity – the number of alleles in a species or population Natural selection acts to increase the number and proportion of advantageous alleles within a population. Genetic diversity Allele – Genetic diversity Allele – different versions of the same gene Genetic diversity Allele – different versions of the same gene Species – Genetic diversity Allele – different versions of the same gene Species – a group of organisms with similar morphological and physiological characteristics that are able to breed together to produce fertile offspring Genetic diversity Allele – different versions of the same gene Species – a group of organisms with similar morphological and physiological characteristics that are able to breed together to produce fertile offspring Population – Genetic diversity Allele – different versions of the same gene Species – a group of organisms with similar morphological and physiological characteristics that are able to breed together to produce fertile offspring Population – a group of organisms of one species living in the same place at the same time Genetic diversity In which two ways can the genetic diversity of a population be increased? Genetic diversity In which two ways can the genetic diversity of a population be increased? • Mutations in DNA to form new alleles • Different alleles being introduced into the population due to migration and reproduction – known as gene flow. Genetic diversity Genetic diversity is what drives natural selection. There are three key stages to natural selection: Genetic diversity Genetic diversity is what drives natural selection. There are three key stages to natural selection: 1. Individuals with more advantageous characteristics that make them more adapted to the environment/ecosystem are more likely to survive. Genetic diversity Genetic diversity is what drives natural selection. There are three key stages to natural selection: 1. Individuals with more advantageous characteristics that make them more adapted to the environment/ecosystem are more likely to survive. 2. These individuals are therefore more likely to reproduce. Genetic diversity Genetic diversity is what drives natural selection. There are three key stages to natural selection: 1. Individuals with more advantageous characteristics that make them more adapted to the environment/ecosystem are more likely to survive. 2. These individuals are therefore more likely to reproduce. 3. The next generation of the population is therefore more likely to have a higher proportion of their alleles coding for those advantageous characteristics. Genetic diversity Over generations, the population will have a much higher proportion of the advantageous allele, meaning it will lead to it becoming more common. This is what evolution is. Genetic diversity Over generations, the population will have a much higher proportion of the advantageous allele, meaning it will lead to it becoming more common. This is what evolution is. Evolution – Genetic diversity Over generations, the population will have a much higher proportion of the advantageous allele, meaning it will lead to it becoming more common. This is what evolution is. Evolution – gradual changes to a species overtime. Genetic diversity Over generations, the population will have a much higher proportion of the advantageous allele, meaning it will lead to it becoming more common. This is what evolution is. Evolution – gradual changes to a species overtime. Adaptation and selection are key factors to evolution. Evolution can lead to huge diversity within species and between species. Bottlenecking Genetic bottlenecking can reduce genetic diversity, and therefore reduce the amount of natural selection taking place. Bottlenecking Genetic bottlenecking can reduce genetic diversity, and therefore reduce the amount of natural selection taking place. Genetic bottlenecking – Bottlenecking Genetic bottlenecking can reduce genetic diversity, and therefore reduce the amount of natural selection taking place. Genetic bottlenecking – an event that cause a big reduction in a population, causing the genetic diversity to decrease Bottlenecking Genetic bottlenecking can reduce genetic diversity, and therefore reduce the amount of natural selection taking place. Genetic bottlenecking – an event that cause a big reduction in a population, causing the genetic diversity to decrease When the individuals in the species die, the number of different alleles in the gene pool of the species decreases, so genetic diversity decreases too. Bottlenecking This leaves a small population with a small gene pool. These individuals will reproduce and form a larger population (providing they are suitable adapted to the environment). Bottlenecking One example of bottlenecking is that off moths. In the industrial revolution, many of the trees were polluted with soot, meaning white moths were more likely to be seen by predators. Bottlenecking This gave an advantage to the darker coloured moths, meaning the gene pool was vastly decreased. Now, most of this species of moth are darker in colour due to this event. Bottlenecking Genetic bottlenecking can be described by the Founder effect. Bottlenecking Genetic bottlenecking can be described by the Founder effect. What is the Founder effect? Bottlenecking Genetic bottlenecking can be described by the Founder effect. What is the Founder effect? The Founder effect describes what happens when a few individuals of a species start a new population from a small gene pool. Bottlenecking The frequency of alleles in the new population may be vastly different to the frequency of alleles in the original population. Bottlenecking The frequency of alleles in the new population may be vastly different to the frequency of alleles in the original population. The most common example, is that a rare allele in the original population is now more frequent in the new population. This can lead to a higher incidence of genetic disease. Bottlenecking The Amish population descended rom a small number of Swiss individuals who migrated to North America. Their population has a small gene pool, so there was little genetic diversity. The Amish typically have remined isolated since their migration due to religious beliefs, so few new alleles have been introduced into the population. This has lead to the population having a high incidence of genetic disorders such as dwarfism and Angelman syndrome Bottlenecking Typically, an allele will only become the most common in a population, providing it is not disadvantageous to the livelihood of the individuals (meaning they can reproduce and pass on their alleles before being killed/dying). Natural selection What are the three key stages to natural selection? Natural selection What are the three key stages to natural selection? 1. Individuals with characteristics that make them more adapted to the environment/ecosystem are more likely to survive. 2. These individuals are more likely to reproduce. 3. The next generation of the population is more likely to have a higher proportion of their alleles coding for those advantageous characteristics. Natural selection Natural selection leads to a population becoming better adapted to the environment/ecosystem. There are three main adaptations you need to be aware of: 1. Behavioural adaptations – Natural selection Natural selection leads to a population becoming better adapted to the environment/ecosystem. There are three main adaptations you need to be aware of: 1. Behavioural adaptations – the ways in which organisms act to increase their chances of survival and reproduction – Natural selection Natural selection leads to a population becoming better adapted to the environment/ecosystem. There are three main adaptations you need to be aware of: 1. Behavioural adaptations – the ways in which organisms act to increase their chances of survival and reproduction – such as a mating ritual. Natural selection 2. Physiological adaptations – Natural selection 2. Physiological adaptations – biochemical changes within an organism’s body to increase its chance of survival – Natural selection 2. Physiological adaptations – biochemical changes within an organism’s body to increase its chance of survival – such as some animals hibernating over winter. This decreases their metabolic rate, meaning energy can be conserved so they don’t have a high demand for energy from food when food is in short supply. Natural selection 3. Anatomical adaptations – Natural selection 3. Anatomical adaptations – structure changes within an organism’s body that increase its chance of survival – Natural selection 3. Anatomical adaptations – structure changes within an organism’s body that increase its chance of survival – wolves evolved to have ‘puppy dog eyes’, meaning they were more likely to be given scraps of food by humans, and therefore more likely to survive. Natural selection There are different types of natural selection that can lead to different allele frequencies in a population. Natural selection There are different types of natural selection that can lead to different allele frequencies in a population. What are the two main types of selection you need to know? Natural selection There are different types of natural selection that can lead to different allele frequencies in a population. What are the two main types of selection you need to know? • Directional selection • Stabilising selection Directional selection Directional selection – Directional selection Directional selection – where individuals with alleles for an extreme type of characteristic are more likely to survive and reproduce. Directional selection Directional selection – where individuals with alleles for an extreme type of characteristic are more likely to survive and reproduce. This typically is a response due to environmental change. Directional selection Directional selection – where individuals with alleles for an extreme type of characteristic are more likely to survive and reproduce. This typically is a response due to environmental change. The most common example is bacteria evolving antibiotic resistance. Directional selection It happens over four stages: Directional selection It happens over four stages: 1. Individuals in the population have alleles coding for resistance to an antibiotic. Directional selection It happens over four stages: 1. Individuals in the population have alleles coding for resistance to an antibiotic. 2. These individuals are more likely to survive if the population is exposed to the antibiotic than those without the allele. Directional selection It happens over four stages: 1. Individuals in the population have alleles coding for resistance to an antibiotic. 2. These individuals are more likely to survive if the population is exposed to the antibiotic than those without the allele. 3. The resistance bacteria survive and reproduce, passing the resistant allele on to the new generation so it increases in frequency. Directional selection It happens over four stages: 1. Individuals in the population have alleles coding for resistance to an antibiotic. 2. These individuals are more likely to survive if the population is exposed to the antibiotic than those without the allele. 3. The resistance bacteria survive and reproduce, passing the resistant allele on to the new generation so it increases in frequency. 4. After many generations, the antibiotic resistant allele is the most common allele in the population. Directional selection Number of individuals Offspring (over generations) Number of individuals Parents low Antibiotic resistance high low Antibiotic resistance high Stabilising selection Stabilising selection – Stabilising selection Stabilising selection – individuals with alleles for characteristic in the middle of a range are more likely to survive and reproduce. Stabilising selection Stabilising selection – individuals with alleles for characteristic in the middle of a range are more likely to survive and reproduce. This occurs when the environment is table, reducing the range of possible characteristics. The most common example is human birth weight. Stabilising selection Humans typically have a range of birth weights, but there can be issues at the extremes: • Small babies are less likely to survive, typically they find it difficult to maintain their body temperature. • Large babies can be difficult to birth, meaning there can be complications, and large babies are also less likely to survive. This means medium sized babies are most favourable, so the weight of human babies shifts to the middle of the range. Stabilising selection Number of individuals Offspring (many generations) Number of individuals Parents light Weight of baby (oz) heavy light Weight of baby (oz) heavy
