5.2.3-5 Natural Selection

Question 1

What is “natural selection”?

Answer 1

Members of a population with phenotypes that make them better adapted to their environments than others tend to survive, reproduce, and pass their adaptations to the next generation at greater frequency than the less “fit” members of the population.

This process leads to change in allele frequency over time as the more “fit” individuals survive and leave more offspring.

Question 2

There are 3 types of natural selection. What are they?

Answer 2

• Stabilization selection
  
  • favors intermediate phenotypes (e.g. median hight, size, etc.)
  • examples:
    
    • human infants weighing less than 7.5 pounds or much more than 7.5 pounds have higher mortality rate
• Directional selection
  
  • favors extreme phenotypes
  • examples:
    
    • insects resistant to DDT
    • bacteria resistant to antibiotics
    • the modern-day horse has adapted from a much smaller ancetor from forest living to grasslands.
• Disruptive selection
  
  • favors both extremes of the range of phenotypes
  • Example: African swallowtail butterfly produces two distinct morphs, each resemble brightly colored but distasteful butterflies of other species.

Question 3

Does natural selection cause changes in the allele frequency of a population?

Answer 3

Yes, natural selection leads to change in allele frequency over time as the more “fit” individuals survive and leave more offspring, increasing the frequency of the “fit” alleles.

Question 4

Define “fitness”.

Answer 4

The measure of an individual’s ability to survive and reproduce.