chapter 4

• What is the process by which individuals in a population show genetic variation?

  Natural selection
• Why do individuals in a population show genetic variation?

  Because of differences in their alleles
• How do new alleles arise in a population?

  Through genetic variation
• What are some examples of selection pressures that affect an organism's survival?

  Predation, competition for resources, and disease
• How do selection pressures influence an organism's chance of survival and reproduction?

  They affect the likelihood of survival and successful breeding
• What happens to individuals with characteristics better suited to selection pressures?

  They have a better chance of survival and are more likely to breed successfully
• What is the outcome for alleles responsible for useful characteristics in a population?

  They are more likely to be passed on to the next generation
• What happens to individuals that are less suited to selection pressures?

  They are less likely to survive and reproduce
• What is the long-term effect of beneficial characteristics in a population?

  They become more common over time
• How do bacteria provide evidence for evolution?

  Bacteria develop random mutations in their DNA that create new alleles.
• What is the significance of random mutations in bacteria?

  They can create new alleles that change the bacteria's characteristics.
• How does antibiotic resistance benefit bacteria in a host being treated?

  A resistant bacterium is better able to survive and reproduce than a non-resistant bacterium.
• What happens to the allele for antibiotic resistance over time in bacteria?

  It is passed on to many of the offspring, increasing its frequency.
• Why does antibiotic resistance provide evidence for evolution?

  It makes bacteria better adapted to environments with antibiotics, increasing their prevalence.
• What is the result of antibiotic resistance becoming more common in bacteria?

  It leads to bacteria being better adapted to environments with antibiotics.
• What is the process by which bacteria develop antibiotic resistance?

  • Random mutations occur in bacterial DNA
  • New alleles are created
  • Some alleles confer antibiotic resistance
  • Resistant bacteria survive and reproduce more effectively
• how do fossils provide evidence for evolution?

  • a fossil is any trace of an animal or plant that lived a long time ago.
  • they are most commonly found in rocks, and generally, the deeper the rock, the older the fossil
  • by arranging fossils in chronological order, gradual changes in organisms can be observed
  • this provides evidence for evolution because it shows how species have changed and developed over billions of years.
• darwin

  • charles darwin came up with the theory of evolution by natural selection
  • he spent 5 years on voyages around the world studying plants and animals on a ship called the HMS beagle
  • he noticed that there was variation between members of the same species and tat those with characteristics most suited to the environment were more likely to survive
  • he noticed that characteristics could be passed down from parents to offspring
  • he wrote his theory of evolution by natural selection to help explain his observations
• Wallace

  • Alfred Russel Wallace was a scientist working at the same time as Darwin
  • he also came up with the theory of evolution independently from Darwin
  • he and Darwin published their papers on evolutions together and acknowledged each other's work
  • Wallace had lots of evidence backing up the theory of natural selection, however it was Darwin"s book 'on the origin of species' that made other scientists pay attention to the theory
• how has modern biology been influenced by ideas about evolution?


  We now understand that all life changes through the proccess of evolution and that the evidence suggests we have all descended from a common ancestor
• what areas of modern biology have been affected?

  Classification - we now classify organisms based on how closely related they are

  antibiotic resistance - we now understand the importance of finishing a course of drugs to prevent resistant bacteria spreading and we know we need to constantly develop new antibiotics to fight newly evolved bacteria

  conservation - we now understand the importance of genetic diversity and how it helps populations adapt to changing environments, this has lead to conservation projects to protect species
• how do fossils show human evolution?


  evidence from fossils suggests that humans and chimpanzees evolved from a common ancestor that existed around 6 million years ago.

  human beings and their ancestors are known as hominids and many different hominid species fossils have been found

  by looking at hominid fossils, you can see how humans have changed over time
• Ardi

  • found in Ethiopia
  • 4.4 million years old
  • her feet structures suggest that she climbed trees - big toes to grip branches
  • long arms and short legs
  • her brain was about the size of a chimpanzee's
  • the structure of her legs indicates that she walked upright
• Lucy

  • found in ethiopia
  • 3.2 million years old
  • arched feet - more adapted to walking that climbing and no ape like big toe
  • her brain was slightly larger than Ardi's but sstill a similar size to a chimp's brain
  • the structure of her leg bones suggests that she walked upright, but more efficiently that Ardi
• Richard Leaky


  scientist Richard leaky organised an expedition to Kenya to look for hominid fossils in 1984

  one of their finds was Turkana boy - a 1.6 million year old fossil skeleton of the species Homo erectus . He was a mixture of human and ape-like features but was more human-like than lucy

  his short arms and long legs are much more human than an ape and his brain size was much larger than lucy's - similar to a human brain sixe

  the structure of his legs and feet suggest that he was evne better adapted to walking upright than lucy
• stone tools

  • homo habilis - made simple stone tools by hitting rocks together to make sharp flakes. Used to scrape meat from the bones or crack bones open
  • homo erectus - sculpted rocks into shapes to produce more complex tools like simple hand - axes. these could be used to hunt, dig, chop and scrap emeat from bones
  • homo neanderthalis - more complex tools, evidence of flint stones and pointed tools
  • homo sapiens - flint tools widely used pointed tools including arrowheads, fish hooks, buttons and needles
• how to find out how old a tool is

  1. looking at structural features, are they simple or more complex?
  2. using stratigraphy - the study of rock layers. older rock layers are normally found below younger layers, so tools or fossils in deeper layers are usually older
  3. ston e tools are ofetn found with carbon containing material eg wooden handles so carbon-14 dating can be used to date this material
• pentadactyl limbs

  • limbs with 5 digits
  • seen in many species
  • in each species, the pentadactyl limb has a similar bone structure, but usually different functions
  • the similarity in the both structure provides evidence that species with a pentadactyl limb have all evolved from a common ancestor
  • if they had all evolved from different ancestors, it would be highly unlikely that they'd share a similar bone structure
• classification


  traditionally, organisms were classified according to similarities and differences in their observable characteristics.

  as technology has improved, this included things you can see with a microscope eg cell structure

  these characteristics were used to classify organisms in the five kingdom classification system
• the five kingdom classification system:

  • animals - fish, mammals, reptiles, etc
  • plants - grasses, trees, etc
  • fungi - mushrooms and toadstools, yeast, etc
  • prokaryotes - all single celled organisms without a nucleus
  • protists - eukaryotic single celled organisms eg elgae
• how has classificationn changed over time?

  • technology has developed and our understanding of things like biochemical processes has increased
  • we are now able to determine the sequence of DNA bases in different organisms' genes and compare them
  • this led to the rethink of our classification system, and the proposal of the three domain system.
  • organisms are now divided into three domains, which are then subdivided into smaller groups used in the five system
• what are the three domains?


  Archaea - look similar to bacteria but are actually quite different - as differences in their DNA and RNA sequences show.

  Bacteria - contains true bacteria such as E. coli

  Eukarya - includes a broad range of organsims such as fungi, plants, animals and protists
• selective breeding


  when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.

  organisms are selectively breed to develop features that are useful or attractive, such as animals with more meat or milk, crops with disease resistance, dogs with good, gentle temperament and plants that produce bigger fruit
• basic selective breeding process

  1. select the plants/animals with the characteristics that you're after
  2. breed them with each other
  3. select the best of the offspring and breed them together
  4. continue this process over several generations and the desirable trait will get stronger and stronger
  5. eventually all offspring will have the characteristic
• why is selective breeding important for agriculture?


  Genetic variation means that cattle wil have better characteristics for producing meat than others. To improve meat yield, a farmer could selectively breed the cows with this characteristic together to get cows with the highest meat yield
• why is selective breeding useful in medical research?


  in several studies investigating the reason for alcoholism, rats have been bred with either a strong preference for alcohol ot a weak preference for alcohol. This has allowed scientists to compare the differences between two different types of rats, including differences in their behaviours and in the way their brains work
• selective breeding disadvantages


  reduces the gene pool - number of different alleles in a population. This is because the 'best' animals are sued for breeding - and they are closely related. Thi is also known as inbreeding

  inbreeding can cause health issues becuase there is a higher chance of the organisms inheriting harmful genetic defects when the gene pool is limited

  there can also be serious problems if new diseases appear - not much variaition mean less chance of resistant alleles being present
• tissue culture


  tissue culture involves growing cells on an artificial growth medium

  plants produced by tissue culture are clones - genetically identical
• tissue culture execution

  1. choose the plant that you want to clone based on its characteristics
  2. remove several small pieces of tissue from the parent plant. you get best results if it is taken from fast growing toot or shoot tips
  3. grow the tissues in a growth medium containing nutrients and growth hormones. this is done under aseptic conditions to prevent growth of microbes that could harm the plants
  4. as the tissue produces shoots and roots, they can be moved to a potting compost to carry on growing
• why is an autoclave used?


  to sterilise the samples