Variation and Evolution

• What are differences in individual characteristics called?

  Variation
• What causes variation in individuals?

  Genetic, environmental, or both factors
• What are the sources of variation in individuals?

  • Genetic differences (inherited genes)
  • Environmental conditions (developmental factors)
  • Combination of genetic and environmental causes
• How does sexual reproduction contribute to variation?

  It produces different combinations of alleles
• What is the only process that creates new alleles?

  Mutations
• What are the characteristics of mutations?

  • Permanent changes in DNA
  • Occur continuously at low rates
  • Often have no effect on phenotype
  • Can be harmful or occasionally useful
• What is the effect of most mutations on phenotype?

  Often have no effect on the phenotype
• What is the likelihood of mutations being harmful compared to being useful?

  More often harmful but occasionally useful
• Key Point

  ABO blood groups are controlled by a single gene, but height is the result of a combination of genes and environment. That is why there is a wide spread of possible heights.
• What is evolution?

  Gradual change in inherited characteristics
• What can evolution lead to?

  Formation of a new species
• What is the theory most scientists support regarding evolution?

  Natural selection
• Who proposed the theory of natural selection?

  Charles Darwin
• What does the theory of natural selection state?

  All species evolved from simple life forms
• How long ago did simple life forms first develop?

  Over three billion years ago
• What are the key points of natural selection?

  • More individuals are born than can survive
  • Individuals show variation in their phenotypes
  • Best-suited phenotypes are more likely to survive
  • Survivors breed and pass on advantageous genes
• Why do different populations of the same species evolve differently?

  Different environments favor different characteristics
• When are new species formed?

  When populations can no longer interbreed
• What happens when two populations of one species become so different?

  They can no longer produce fertile offspring
• Key Point

  When scientists describe natural selection now, they can talk about alleles being passed on, which will cause changes to the phenotypes in a population.
• What was not known when Darwin's theory of evolution was published?

  The mechanism of inheritance and variation
• What proved that characteristics are passed on by genes?

  Research in the early 20th Century
• What provides substantial evidence for evolution?

  Fossils
• What are fossils?

  Remains of organisms from the past
• How are fossils formed?

  From hard parts or preserved traces of organisms
• What are the ways fossils may be formed?

  • From hard parts of animals
  • From parts that have not decayed
  • When parts are replaced by other materials
  • As preserved traces (footprints, burrows)
• How have scientists used fossils in evolution studies?

  To observe gradual changes in organisms
• What is a problem with fossils?

  There are gaps in the fossil record
• Why are there gaps in the fossil record?

  • Many early life forms were soft-bodied
  • Traces may have been destroyed by geological activity
• What supports the theory of evolution besides fossils?

  Genetic data
• What do slight mutations in DNA allow scientists to do?

  Create accurate evolutionary family trees
• How can antibiotic-resistant bacteria evolve?

  Through rapid reproduction and mutations
• What is the process of developing antibiotic-resistant strains of bacteria?

  1. Bacteria reproduce rapidly
  2. Mutations occur during reproduction
  3. Some bacteria become antibiotic-resistant
  4. Resistant bacteria survive and reproduce
• What is still debated today regarding evolution?

  The origin of life