BIOB51 Lecture 3 and 4 Notes UTSC

BIOB51 – Lecture 3

Natural Selection: differences in average reproduction of individuals with different
phenotypes in a population.
• It favours traits that increase fitness
Natural Selection Notes:
1. Natural selection will lead to evolutionary change only if the variable traits phenotypic differences are due to genotypic differences
o It can also occur even if the variation doesn’t have a genetic basis FLAGGED:

• WRONG: Natural selection occurs if traits that lead to variation in fitness
  
• RIGHT: natural selection occurs whenever variation in phenotypic traits leads to
  variation in fitness
  

o Natural selection acts on phenotypes
o Natural selection leads to evolutionary change if there is a genetic basis to
phenotypic variation
▪ For example, the hawk seeing the yellow snakes more easily than the
green snakes. This results in the offspring population having more green
snakes.
o What if the phenotype isn’t heritable, and the body colour depends on the diet?

• ▪  Green colour would still be naturally selected since yellow snakes are killed at a higher rate.
  
• ▪  There is no evolutionary change. The population remains as 50% for each colour
  

2. Natural selection acts on individuals, evolution occurs in populations

o o o

In the above example, the population of snakes has evolved.
The individual snakes haven’t changed colour
Contrast with Lamarak: individuals change in response to the environment.
▪ Natural selection is basically sifting through the traits to sort the individuals

3. Natural selection is not random
o Individuals can deal better with their environment can reproduce more than their competitors
▪ The traits that are selected are those that gave high fitness o This is confusing since mutation is random.
Evidence for Evolution: Microevolution and Macroevolution:
• Microevolution:
o Focuses on process issues.

o It is the maintenance or change in traits over a few generations. o It occurs within species
o It is the evidence that selection can produce evolutionary change o It focuses on the evidence that species change through time
• Macroevolution:
o It focuses on the origin of species or higher taxonomic groups.
o The origin/change in traits that define new taxa
o It focuses on the evidence that ancestral species can give rise to diverse
descendants
Evolution under Domestication:

• Many varieties from a single ancestor. For example, species of dogs
  o Another example is the Wild Mustard plant. It was selected for different traits to
  make new vegetables like cauliflower, etc.
  
• The degree of the curve of the muzzle depends on the development of the gene.
  
• Artificial selection vs. natural selection:
  
• Macroevolution:
  o Evidence that organisms descended from earlier forms Fossil Record:
  
• Fossils: traces of any organisms that lived in the past
  
• Fossil record: is the total worldwide collection of fossils
  o New species appear continuously through time but they don’t appear at the same time
  o Life is ancient (approximately 3.5 billion years ago)
  ▪ There has been a lot of time for evolution to occur
  
• Vestigial structures
  

BIOB51 – Lecture 4
Homology: when two types of organism have similar characteristics and traits.
• There are two types:
o Structural homology: for example, the vertebrate forelimb o Vestigial structures:
▪ Don’t serve a function in one lineage but do in another
Fossil Record:

• Mammals evolved on land approximately 250 mya
  
• About 50 million years ago, whales were
  

o The whales can be traced back to mammals due to their vestigial structures
o The ambuocetus has forelimbs
o The basilosaurus has limbs but is not connected to the spinal cord
o The modern baleen whale has the femur and pelvis but it isn’t attached to the
spinal cord
▪ They are homologous to our spinal cord

• A vestigial structure that was used many years ago may not be used anymore for that specific function, but instead for a new function
  o The residual femur in whales helps in sexual function
  
• When phylogenetic trees are used, it can be seen where feathers and flight originated
  from
  o It can help to see common ancestry
  Developmental Homology: organisms that are now classified together have similar embryonic stages, although they have different adult forms. They also have similar control/developmental genes
  Molecular Homology:
  
  • Humans have a universal genetic code
    
  • Some more codes are possible and could possibly produce less errors
    

o This could remove the risks of viruses that come from other species. For example, HIV, H1N1.
o Humans and animals share a genetic code so it is easy for viruses to come

• Large sections of DNA are similar in species, even for functionless DNA
  
• Chromosomal homology: when closely related species have similarities in their physical
  arrangement of DNA.
  

o Humans have one chromosome less when compared to non-human primates o Human chromosome 2: when two chromosomes are found in non-human
primates
• Some organisms that are used to investigate molecular, physiological, or cellular basis of
human disorders are fruit fly, chimpanzees, etc

Evidence Suggests:

• Extensive similarity as predicted by descent with modification
  
• Homologous: traits found in different species that are similar because they have been
  inherited from a common ancestor
  Microevolution:
  

• Evolution of Brassica rapa, the flowering time is in accordance to a drought.
o The flowering time for the plants has changed over 7 years due to the absence of a
drought.
Natural Selection in Humans:

• When some humans live in high altitudes, the oxygen pressure is 45% lower than at sea level.
  
• This has a negative effect on your health.
  
• In Tibet, there is low environmental oxygen availability.
  o The observed variation is in the blood oxygen content of village women.
  o The women had differences due to the variation in oxygen saturation genotypes. o People with AB or BB genotypes have an average oxygen saturation
  o Homozygous AA genotype have a 10% higher average blood oxygen saturation
  •