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The development of understanding of genetics and evolution

6.3.1 Theory of evolution (biology only)

See 6.2.2  Evolution

6.3.2  Speciation (biology only)

Speciation

  • Populations become extremely varied & no interbreed anymore
  • Formation of new species (a group of organisms able to interbreed & produce fertile offspring)

Charles Darwin – see 6.2.2  Evolution

Alfred Russel Wallace

  • Published joint writings with Darwin in 1858
  • Best known for his work on warning colouration in animals & his theory of speciation

Describe the steps which give rise to new species

  1. Genetic variation – each population has wide range of alleles that control characteristics
  2. Natural selection
  3. Speciation
  4. Isolation
  • 2 population of a species become geographically separated
  • Different mutations take place in isolated groups
  • Overtime species evolve to be different to each other – cannot interbreed

6.3.3 The understanding of genetics (biology only)

Gregor Mendel

  • Carried out breeding experiments on pea plants
  • Inheritnace of each characteristic is determined by ‘units’ (genes) that are passed onto descendants unchanged

Describe the development of our understanding of genetics including the work of Mendel

  1. Mid-19th century – Gregor Mendal carried out breeding experiments on plants
  2. Late 19 – behaviour of chromosomes during cell division was observed
  3. Early 20th century – chromosomes and Mendel’s ‘units’ behaved in similar ways – led to the idea that the ‘units’, now called genes, were located on chromosomes.
  4. Mid-20th century – structure of DNA was determined & the mechanism of gene function worked out

Why using large no of offspring plants can improve the investigation (2)

  • Large no so more reliable
  • Anomalies can be identified

Why importance of Mendel’s discovery wasn’t recognised at that time? (2)

  • DNA not discovered
  • Mendel wasn’t considered as a scientist / wasn’t part of academic establishment

6.3.4 Evidence for evolution

See 6.3.5  Fossils, 6.3.6  Extinction & 6.3.7  Resistant bacteria

6.3.5 Fossils

Fossils – the ‘remains’ of organisms from millions of years ago, which are found in rocks

Where are fossils formed? (3)

  • Parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
  • When parts of the organism are replaced by minerals as they decay
  • As preserved traces of organisms, such as footprints, burrows and rootlet traces

How fossils are formed?

  • Animal / plant dies & body covered in sediment
  • Soft parts decay
  • Hard parts (bones) don’t decay and are replaced by minerals
  • Lack of O2 and moisture prevent microorganisms to decay
  • Preserved traces of organisms eg footprints, burrows & rootlet traces
  • Soft parts decay, bones / shells don’t decay

Suggest how insects came to be preserved in the amber (2)

  • Trapped and engulfed by amber
  • Prevented decay (due to lack of O2 and moisture)

How can fossils give evidence for evolution? (1)

  • Show how organisms changed as life developed on Earth

Why scientists are uncertain about how life began on Earth? (1)

  •  Insufficient evidence

Suggest 2 reasons why there are gaps in the fossil record (2)

  • Fossils not found yet
  • Fossils are destroyed by geographical activities eg volcanoes
  • Conditions not right for fossilisation

6.3.6 Extinction

Extinction – occur when there are no remaining individuals of a species still alive

Why a species may become extinct? (3)

  • Environmental changes – species can’t adapt fast enough
  • Natural disaster eg flooding, drought
  • New predator / disease eg no resistant alleles
  • Human activities eg hunting, deforestation
  • Competition for food / mates
  • Catastrophic event wipe out species eg asteroid killed dinosaurs

6.3.5 Resistant bacteria

Bacteria can evolve rapidly because they reproduce at a fast rate

How pathogens produce new strains via mutation (6)

  1. Mutations of bacterial pathogens produce new strain
  2. Some strains might be resistance to antibiotics and so are not killed
  3. Some survive and reproduce by binary fission
  4. Gene for resistance passed on to offspring so pathogen being immune
  5. Population of resistant strain rises
  6. Resistant strain then spread coz ppl not immune to it & has no effective treatment

Methicillin-resistant Staphylococcus aureus (MRSA)

  • Bacterium that has evolved to be resistant to lots of antibiotics (superbugs bacteria)

How to reduce rate of development of antibiotic resistant strains? (3)

  • Doctors reduce use of antibiotics for non-serious / viral infections
  • Patients complete course of antibiotics to kill all bacteria so none survive to mutate & form resistant strains
  • Restrict agricultural use of antibiotics

Development of new antibiotics

  • Costly
  • Slow
  • Unlikely to keep up with the emergence of new resistant strains