Inheritance, Variation and Evolution

• Gregor Mendel is considered the father of modern genetics
• Mendel did experiments using pea plants to investigate inheritance of traits
• During Mendel's experiments, he looked at colours of flowers, colours of pea pods and height for the inherited traits.
• Speciation is the evolutionary process by which populations evolve to become distinct species.
• Antibiotic Resistance and Fossil Records provide evidence for the Theory of Evolution
• Charles Darwin proposed the Theory of Evolution
• Variation- Differences in the characteristics (phenotypes) of individuals within a population
• Variation depends on both genetic factors and environmental factors
• A change in genetic material / DNA is called a mutation.
• Evolution is the process by which the inherited characteristics of a population change over time due to natural selection. In some cases, this may result in the formation of a new species.
• Most of the time, mutations have no effect but when they do, it is more likely disadvantageous than advantageous
• Selective Breeding is the process of breeding organisms to produce offspring with desired characteristics. This process occurs when the best of a group of animals/plants (based on the desired characteristic) are selected and bred together to produce offspring with the desired characteristic. This process is repeated many times.
• Disadvantages of Selective Breeding


  .Reduces the gene pool of the population since certain alleles are being selected that will code for the desired traits

  .Best individuals are often closely related and breeding closely related organisms (Inbreeding) causes offspring to be prone to disease and to inherit defects

  .Less variation in a population (raises risk of a disease wiping the whole population out)
• Genetic engineering- the process of taking the gene that codes for a desirable characteristic in one organism and transferring it to another organism so that it can develop the same trait. This can occur between different species
• Genetic Engineering = Genetic Modification
• The Human Genome Project(2003) was an international project aimed at identifying all the genes in the human body. It involved scientists working together to sequence DNA from humans and other organisms. The aim was to identify all the genes in the human body and understand how they work. They also wanted to compare these findings with those found in other organisms.
• Gene Therapy- a way of treating inherited disorders caused by faulty genes by introducing a healthy version of the gene into the patient's body
• Gene Therapy: Name one problem and the solution


  Problem: Since the faulty gene is in all cells, the healthy gene would need to be transferred to all cells which is very difficult

  Solution: Transfer the healthy gene at an early stage of development so the gene is passed on as the person develops
• Advantages of GM crops

  • Crops with desirable characteristics can be produced which leads to more food being produced for less money
  • Food costing less to be produced is important for developing countries and to reduce world hunger
  • Crops can also produce special nutrients
• Disadvantages of GM crops

  • We don't know how GM crops may affect our health
  • GM crops may get into the wild, outcompete local crops and change the whole ecosystem
• Steps for transferring genes

  1. Locate the wanted gene and isolate it using enzymes
  2. Place the gene inside of a vector (e.g. a virus or plasmid)
  3. Transfer the vector to the organism that you want to have the gene
  4. The organism will start producing the protein the gene codes for
• Steps for cloning through nucleus transplant

  1. Take an egg cell from a donor female and remove its nucleus so that you have an enucleated egg cell
  2. Take an adult body cell (e.g. skin cell) from the organism you want to clone and remove its nucleus
  3. Put the nucleus from the adult body cell into the enucleated egg cell
  4. Stimulate the egg cell electrically so that it acts like a zygote and divides by mitosis to form an embryo
  5. Implant the embryo into the uterus of a surrogate mother where it will develop into a fetus and be born normally
• Genetic engineering can be used to place human genes into the DNA of different organisms. An organism that has DNA from another organic is called transgenic. We can use this process to make animals produce human proteins in their milk which can be extracted and used in many ways like medicine. A transgenic animal can be cloned.
• Steps for cloning by embryo transplant

  1. Pick a male and female cow with the most desirable traits
  2. Take the male's sperm and fertilise an egg from the female to form a zygote
  3. Let the zygote develop into an embryo(ball of identical cells)
  4. Separate the embryo into a lot of smaller embryos
  5. Implant each embryo into the uterus of a surrogate cow
  6. The offspring will all be identical clones
• Lamarck's Theory of Evolution(with giraffe example)

  1. All individuals in a species started at the same point with a certain characteristic (Giraffes started with shorter necks for shorter vegetation)
  2. To survive, they adapt to their environment by developing an acquired characteristic across their lifetimes. (They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime)
  3. The acquired trait is passed on to offspring and future generations continue to have the trait (successive generations have longer necks for reaching higher branches)
• Lamarck's theory was proven incorrect by modern genetics: characteristics acquired by an organism during its lifetime do not affect the DNA sequence of the organism and therefore, cannot be passed down from one generation to the next. 
• Charles Darwin made important observations such as:

  1. Individual organisms within a species show a wide range of variation for a specific trait.
  2. Darwin observed variations between species adapted to different environments.
  3. Older layers of rock contained fossils of less complex organisms, while more recent layers showed more complex organisms.
• In his book, "On the Origin of Species", Darwin proposed that natural selection is the driving force behind the gradual development of species over time. Russel Wallace independently arrived at a similar conclusion to Darwin, and they later presented a paper together, providing additional evidence for the theory.
• Darwin's Theory of Evolution(with giraffe example)

  1. Organisms in a species have variations for different traits(Some giraffes naturally had longer necks than others)
  2. Some have a trait that makes them better adapted to their environment(Giraffes with longer necks could eat leaves from taller trees)
  3. Those with this trait survive and reproduce, passing on the trait to future generations(Giraffes with longer necks had a higher chance of surviving, reproducing and passing on the trait)
  4. This repeated process causes change in the species (this process produced modern giraffes with very long necks)
• Steps for Plant Cloning by 'Cutting'

  1. Find the plant you want to clone
  2. Cut off a part of the plant ( ideally a growing shoot or branch)
  3. Plant the cutting in the soils along with nutrients and maybe some hormones
  4. The cutting will grow into an identical clone of the original plant
• Steps for Cloning Plants by Micropropagation

  1. Find the plant with desirable characteristics you want to clone
  2. Extract tiny pieces of the plant (explants) from the tip of the stem
  3. Sterilise the explants to remove any microorganisms
  4. Place the explants in a nutrient medium like agar along with growth hormones to let them develop into calluses (small masses of cells)
  5. Transfer the calluses to let them grow into plantlets(baby plants)
  6. Transfer the plantlets into pots so that they can grow into identical clones of the original plant
• Fossils are the remains of organisms from the past. We can use fossils as evidence for evolution by using them to identify the small changes that have occurred to various species over time.
• How can fossils form

  1. Hard body parts, such as bones and shells, which decay very slowly, are gradually replaced by minerals, forming rock-like substances with the same size/shape.
  2. Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock.
  3. Some organisms may not decay at all due to the environment they're in which doesn't have the right conditions for decaying microorganisms like heat, moisture or oxygen. For example, dead animals and plants can be preserved in amber, peat bogs, tar pits, or ice.
• Why don't we have a complete fossil record?

  .Very early life forms were soft-bodied meaning they decayed quickly

  .Fossils formed a long time ago could have been destroyed by now by geological activity such as earthquakes/volcanoes
• Reasons for Extinction

  .Environment changes too quickly e.g. habitat is cut down or global warming

  .New disease wipes out the whole species

  .New predator wipes out the whole species

  .New species outcompetes the other species for resources

  .Catastrophic event e.g. asteroid
• Extinction- no individuals of that species remain
• A species is a group of genetically similar organisms that can interbreed and produce fertile offspring.
• Process of Speciation

  1. Two populations of a species are somehow separated from each other (isolation)
  2. The different populations experience different environments
  3. The different environments mean that the populations experience natural selection differently(different environments mean that different traits are desirable)
  4. After many generations, the two populations become so physically/genetically/physiologically (behaviour) different that they can no longer interbreed and produce fertile offspring and therefore they are separate species
• Russel Wallace came up with the theory of speciation.
• How Antibiotic Resistance occurs

  A person takes/ is prescribed an antibiotic to cure a bacterial infection. A mutation (change in DNA) occurs in some bacteria meaning that the bacteria is resistant (less affected) to the antibiotic. The resistant bacteria survive while the antibiotic kills the non-resistant bacteria. The resistant bacteria now doesn't have to compete for resources and is, therefore, able to multiply abundantly (more mutations can occur = higher resistance). This resistant bacteria can spread to other people. The antibiotic would not work for people infected by this bacteria.