GENETIC DIVERSITY AND ADAPTATION

• GENETIC DIVERSITY: the total number of different alleles of genes in a species or population. The differences in DNA.

  • All members of the same species have the same genes. Organisms of the same species differ in their combination of alleles, not their genes.
• POPULATION: a group of individuals of the same species that live in the same place and can interbreed

  • a species consists of one or more populations
• IMPORTANCE OF GENETIC DIVERSITY: 1

  1. greater the genetic diversity, the more likely that some individuals in a population will survive an environmental change
  2. this is because of a wider range of alleles + therefore a wider range of characteristics
  3. this gives a greater probability that some individual will possess a characteristic thats suited to the new environmental conditions
  4. this allows populations to adapt to their environment. If a population has a low genetic diversity, it may not be able to adapt to a change in the environment and could be wiped out by a single event eg, disease.
• IMPORTANCE OF GENETIC DIVERISTY

  5. This would cause genetic bottlenecking

  6. Genetic diversity is a factor that enables natural selection to occur
• HOW IS GENETIC DIVERSITY INCREASED?

  • MUTATIONS: new alleles formed. Some of which will be advantageous but others could lead to problems
  • MEIOSIS: crossing over and independent segregation
  • RANDOM FERTILISATION: random which sperm fertilises which egg
  • GENE FLOW: different alleles being introduced into a population when individuals from another population migrate into it and reproduce
• GENETIC DRIFT: the change in frequency of an existing gene variant in a population due to random chance

  • it may cause gene variants to disappear completely and thereby reduce genetic variation
• GENETIC BOTTLENECKING: an event that causes a big reduction in a population

  • for example, when a large number of organisms within a population die before reproducing. This reduces the number of different alleles in the gene pool and so reduces genetic diversity. The survivors reproduce and a larger population is created from a few individuals.

  
• THE FOUNDER EFFECT

  1. A small number of (mother / ancestral) organisms go from the original population to a new place
  2. a population begins from a small population
  3. there’s a small number of alleles in the gene pool
  4. therefore a reduced genetic variation
  5. a non random sample of the genes
  6. higher chance of genetic disease

  
• NATURAL SELECTION: occurs when the allele codes for a characteristic that increases the chances of an organism surviving (advantageous allele), its frequency within the population can increase. This leads to evolution.
• NATURAL SELECTION AND EVOLUTION

  Randomly occurring mutations sometimes result in a new allele being formed

  • this can be harmful, which usually means that the mutated allele quickly dies out
  • some mutations can produce alleles that are beneficial to an organism (eg. A protein is produced that works better than the original) helping the organism to survive in certain environments
• EVOLUTION: the gradual change in species over time. It has led to the huge diversity of living organisms on earth. Adaptation and natural selection are both key factors in evolution.
• WHAT ARE KEY FACTORS IN EVOLUTION?

  • adaptation
  • natural selection
• ADVANTAGEOUS

  What is ‘advantageous’ depends upon the environmental conditions at any one time. An advantageous allele in one environment may be a less advantageous allele in another.
• PROCESS OF NATURAL SELECTION RESULTING IN EVOLUTION IN A POPULATION: 1

  1. within any population / species there’ll be a gene pool containing a wide variety of alleles
  2. random mutation of alleles within this gene pool may result in a new allele of a gene which I most cases will be harmful. However in certain environments, the new allele or a gene might give its possessor an advantage over other individuals in the population.
• PROCESS OF NATURAL SELECTION RESULTING IN EVOLUTION IN A POPULATION: 2

  3. these individuals will be better adapted - therefore more likely to survive in their competition with others so are more likely to obtain the available resources and so grow more rapidly and live longer. As a result, they will have a better chance of breeding successfully and producing more offspring. Only those individuals that reproduce successfully will pass on their alleles to the next generation

  4. This means that a greater property on of the next generation inherits the beneficial allele
• PROCESS OF NATURAL SELECTION RESULTING IN EVOLUTION IN A POPULATION: 3

  5. They in turn, are more likely to survive, reproduce successfully and pass on their genes

  6. So the frequency of the beneficial allele in the population increases from generation to generation with the less advantageous allele decreasing

  7. Over the generations this leads to evolution as the advantageous allele becomes more common in the population
• ADAPTATIONS

  1. behavioural
  2. Physiological
  3. anatomical
• BEHAVIOURAL ADAPTATIONS: ways an organism acts that increases its chance of survival
• PHYSIOLOGICAL ADAPTATIONS: processes inside an organisms body that increases its chance of survival
• ANATOMICAL ADAPTATIONS: structural features of an organisms body that increase its chance of survival
• BEHAVIOURAL ADAPTATIONS EXAMPLES

  • PLAYING DEAD: possums do this to escape being attacked
  • MIGRATION: birds do this so they have a suitable place to breed and raise their offspring as seasonal variation can be a limitation in some areas
  • DANCING BEFORE MATING: scorpions do this to increase the chance of successful mating
• PHYSIOLOGICAL ADAPTATIONS EXAMPLES

  • HIBERNATE: brown bears - they lower their rate of metabolism (all the chemical reactions taking place in their body) over winter. This conserves energy, so they don’t need to look for food in the months where it’s scarce, increasing their chance of survival
  • SOME BACTERIA PRODUCE ANTIBIOTICS: to kill other species of bacteria in the area - this means there’s less competition, so they’re more likely to survive
  • temperature regulation
  • release of toxins or poisons
  • releasing antifreeze proteins to avoid freezing in cold environments
• ANATOMICAL ADAPTATIONS EXAMPLES

  • polar bears CAMOUFLAGE - can sneak up on prey which increases their chances of survival as they’ll get food
  • giraffes LONG NECKS - to reach food which increases their chances of survival as they can grow and reproduce - example of natural selection and evolution
  • otters have STREAMLINED SHAPE - makes it easier to glide through water to catch prey and escape predators, increasing chance of survival
  • whales have a THICK LAYER OF BLUBBER - helps to keep them warm in the cold sea which increases their chance if survival in places where their food is found
• TYPES OF SELECTION

  SELECTION: when better adapted organisms survive to breed and less well adapted organisms fail to do so

  • most characteristics are controlled by poly genes (more than one gene) and are influenced by the environment. If the environment changes, advantageous phenotypes will change
  • the effect of the environment on poly genes produces individuals in a population that vary about the mean. When you plot this variation on a graph you get a normal distribution curve
  • directional selection and stabilising selection affect this normal distribution curve

  
• DIRECTIONAL SELECTION

  • ONE DIRECTION FAVOURED
  • change to the environment
  • one extreme phenotype favoured
  • individuals with alleles towards this extreme more likely to survive and reproduce
  • mean phenotype changes
  • changes characteristics of the population

  
• EXAMPLE OF DIRECTIONAL SELECTION

  BACTERIA EVOLVING ANTIBIOTIC RESISTANCE

  Some individuals in a bacterial population have alleles that give them resistance to an antibiotic. The population is exposed to the antibiotic, killing the bacteria without the resistance allele. The resistant bacteria survive and reproduce without competition, passing on the allele that gives antibiotic resistance to their offspring. After some time, most organisms in the population will carry the antibiotic resistance allele.

  
• STABILISING SELECTION

  • AVERAGE PHENOTYPE FAVOURED
  • stable environment
  • mean phenotype favoured
  • individuals with alleles for characteristics towards the mean of the range are more likely to survive and reproduce
  • mean phenotype remains the same
  • reduces the range of possible characteristics as extremes are eliminated but preserves the main characteristics of a population

  
• EXAMPLE OF STABILISING SELECTION

  HUMAN BIRTH WEIGHT

  Humans have range of birth weights. Very small babies = less likely survive bc have a high SA:V ratio = means they find it hard to maintain body temperature. This puts pressure on their respiratory + cardiac systems, which can be fatal. large babies = less likely to survive too. Giving birth to large babies =difficult bc large size makes it harder to fit through mother’s pelvis - can lead to complications for mother + child. Conditions most favourable for medium-sized babies, so weight of human babies tends to shift towards middle of range