Topic 5.4 Evolution

Question 1

5.4.1 Define evolution.

Answer 1

Evolution: the cumulative change in heritable characteristics of a population.

Question 2

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.

Answer 2

Fossil Records

• paleontologists discovered that existing life today isn’t identical to life in past, but is similar
  
  • suggests organisms have evolved
• selective breeding provides a record of recent changes in heritable characteristics. As animals with most desirable genetic characteristics were bred together, breeders noticed certain varieties of animals had adopted characteristics that didn’t exist before
  
  • selective breeding is evidence that evolution happens due to an accumulation of small changes (but selective breeding isn’t the driving force of evolution in natural ecosystems)
• homologous anatomical structures are similar in form & function yet are found between seemingly dissimilar species
  
  • e.g. five-fingered (pentadactyl) limb shared by humans, whales and bats; although # and shape of bones may vary and function is different, basic placement & format is the same
  • evidence that the animals in question have evolved from common ancestor

Question 3

5.4.3 State that populations tend to produce more ________ than the environment can support.

Answer 3

Populations tend to produce more offspring than the environment can support.

Question 4

5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.

Answer 4

• more offspring = less resources available
  
  • supply & demand problems will arise
• therefore increased competition
• therefore increased mortality rate as weaker members fail to obtain vital resources b/c environment cannot support large population
• thus, potential overproduction of offspring = struggle for survival

Question 5

5.4.5 State that the members of a species show _________.

Answer 5

Members of a species show variation.

Question 6

5.4.6 Explain how sexual reproduction promotes variation in a species.

Answer 6

Sexual reproduction promotes variation in a species through meiosis & fertilization.

• Independent assortment of chromosomes when cells split during meiosis will produce egg cells and sperm cells with different combinations of chromosomes, depending on how maternal & paternal chromosomes split during anaphase
• Crossing over, when genetic info is traded b/w non-sister chromatids while in bivalents, increases # of potential gamete variations
• Random ferilization involves an egg cell being penetrated by one of many sperm cells present in female’s body; many possible variations

Question 7

5.4.7 Explain how natural selection leads to evolution.

Answer 7

• overproduction of offspring = competition
• each offspring will have natural variation due to genetic differences
• individuals w/ harmful variation/genetic characteristics = poorly adapted to environment & less likely to survive
• individuals w/ useful variation/genetic characteristics = well adapted to environment & more likely to survive and reproduce (natural selection)
  
  • thus, successful genetic characteristics passed onto next generation
• over many generations, the accumulation of changes in the heritable characteristics of a population will result in evolution

Question 8

5.4.8 Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

Answer 8

Antibiotic resistance in bacteria

• e.g. some strains of tuberculosis
• bacteria reproduce asexually → generally don’t change often
• may develop resistance to antibiotics through changes in their genetic makeup through mutations or plasmid transfer
  
  • plasmid transfer = 1 bacterium donating antibiotic resistance genetic info to another bacterium through plasmid
• natural selection means only those with resistance will survive & rest will die if exposed to antibiotic
• new antibiotics must be made on regular basis as bacteria keep evolving and become resistant to multiple antibiotics

Peppered Moth

• 2 types of moth: 1 lighter & one darker
• before Industrial rev., lighter moth predominated & darker moths eaten more often b/c they stood out against the light trees upon which they rested
• during Industrial rev., trees covered in soot from factories → camouflaged dark moths & light moths were eaten more
• light moths became less adapted to environmental change ∴ most died off while darker moth population increased