B15 - Genetics and evolution

• Genetics


  The study of heredity and how traits are passed from parents to offspring
• Evolution


  The gradual change in the characteristics of living organisms over successive generations, resulting in the development of new species
• Gregor Mendel


  • Austrian monk who carried out breeding experiments with peas and discovered the basic laws of heredity
• Mendel's work


  1. Cross-breeding peas

  2. Observing and recording offspring

  3. Identifying patterns of inheritance
• Dominant and recessive traits

  Dominant traits are expressed even if only one copy is present, recessive traits are only expressed if two copies are present
• Mendel's pea traits


  • Smooth/wrinkled
  • Green/yellow
• Mendel's work was not recognised in his lifetime, but later became the foundation of modern genetics
• Chromosomes and Mendel's 'units of inheritance'


  Behave in similar ways, leading to the idea that genes are located on chromosomes
• DNA is the material of inheritance and explains how genes work
• The discovery of the DNA double helix structure led to an explosion of genetic research
• The gene theory states that genes code for proteins, which is how they have their effect
• Natural selection


  The process by which organisms better adapted to their environment tend to survive and produce more offspring, leading to the gradual evolution of species
• Lamarck proposed that changes acquired during an organism's lifetime could be inherited, which is now known to be incorrect in most cases
• Charles Darwin


  • Proposed the theory of evolution by natural selection based on observations made during his voyage on the HMS Beagle
• Darwin's theory of evolution by natural selection

  1. Variation within a species

  2. More offspring produced than can be supported by the environment

  3. Survival of the fittest

  4. Passing on of advantageous traits to offspring
• Darwin's theory was controversial and took time to be accepted, as it challenged religious beliefs about the origin of life
• Darwin spent years gathering evidence to support his theory, including observations of species on the Galapagos Islands and breeding experiments with pigeons
• Darwin published his theory in the book 'On the Origin of Species', which caused a sensation and is still in print today
• Alfred Russel Wallace independently proposed the theory of evolution by natural selection. He published joint writings with Darwin in 1858 which prompted Darwin to publish The Origin of Species the following year (1859)
• Wallace


  • Worked worldwide gathering evidence for evolutionary theory
  • Best known for his work on warning colouration in animals and his theory of speciation
• Speciation


  1. Isolation: where two populations of a species become separated

  2. Genetic variation between the populations

  3. Natural selection that operates differently on the two populations

  4. Speciation: where the populations become so different that successful interbreeding is no longer possible
• A build-up of evidence over time has led to our current understanding of the theory of speciation
• There is no record of the origins of life on Earth. It is a puzzle that can never be completely solved - no one was there to see it! Scientists don't even know exactly when life on Earth began. However, most think it was somewhere between 3 and 4 billion years ago
• Darwin's theory of evolution by natural selection is now widely accepted as the best explanation of the living world. The understanding of genetics and how characteristics are passed to offspring in the genes gives a clear mechanism for the process and helps supply the supporting evidence needed
• Fossils


  The remains of organisms from millions of years ago that are found preserved in rocks, ice, and other places
• How fossils are formed

  1. When an animal or plant does not decay after it has died

  2. Harder parts of the animal or plant are replaced by minerals as they decay and become part of the rock

  3. Mould fossils are formed when an impression of an organism is made in mud and then becomes fossilised

  4. Cast fossils are made when a mould is filled in

  5. Rock fossils are the most common form of fossils
• The fossil record is not complete for several reasons: many of the very earliest forms of life were soft-bodied organisms, most organisms that died did not become fossilised, and there are many fossils that are still to be found
• In spite of all these limitations, the fossils that have been found can still give you a 'snapshot' of life millions of years ago
• Ice fossils


  Fossils preserved almost intact in ice
• Ice fossils


  • Give a clear insight into what an animal looked like
  • Can tell us what an animal had been eating or the colour of a long-extinct flower
  • Scientists can even extract the DNA and compare it to the DNA of modern organisms
• Fossils are the remains of organisms from millions of years ago that can be found in rocks, ice, and other places
• Fossils may be formed in different ways including the absence of decay, parts replaced by minerals as they decay, and as preserved traces of organisms
• Fossils give us information about organisms that lived millions of years ago
• It is very difficult for scientists to know exactly how life on Earth began because there is little valid evidence. Early forms of life were soft bodied so left few traces behind and many traces of early life have been destroyed by geological activity
• Fossils


  • They help scientists to understand how much organisms have changed since life developed on Earth
  • Only small pieces of skeletons or little bits of shells have been found
• Fossil record


  • It is very complete for a few animals, including the horse
  • They can show how some organisms have changed and developed over time
  • They can help reconstruct the ecology, climate, and environment of millions of years ago
• Fossil sharks from millions of years ago look very like modern sharks. They evolved early into a form that was almost perfectly adapted for their environment and their way of life. Their environment has not changed much for millions of years, so sharks have also remained the same
• Fossil skulls of a group of animals known as perissodactyls


  • hyracotherium
  • mesohippus
  • merychippus
  • pliohippus
  • modern horse (Equus)
• Throughout the history of life on Earth, scientists estimate that about 4 billion different species have existed. Yet scientists currently estimate that there are only 8.7 million species of organisms are alive today. The rest have become extinct
• Extinction


  The permanent loss of all the members of a species