Download natural selection - Bloor

Name: ________________________________
Date: _______________________
Natural Selection
Descent with Modification
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Darwin proposed that the descendants of the earliest organisms spread into various habitats very
millions of years.
In these habitats, they accumulated different _____________________________________ to
diverse ways of life.
Darwin called this process __________________________________
Darwin never actually used the term “evolution”. “Evolution” came into use later and replaces
“descent with modification.”
Hardy-Weinberg Principle
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Evolution can also be described ________________________
Explained the relationship between ______________________ with in a population using a
mathematical equation
In __________ populations in which only ________________ is at work, allele frequencies are
expected to remain ______________ from generation to generation
5 conditions: we talked about them last class
1. Small population
4. Migration
2. Non-random mating opportunities
5. Natural selection
3. Genetic mutation
Types of Selection
Many factors influence how selection can operate on individual phenotypes:
Stabilizing selection
Environment selects the ________________________ phenotype
Eg. Bill length in hummingbirds fits food source
2. Directional selection
 Environment favours individuals with ____________________ variations of a trait
 Eg. Hummingbird population moves to new habitat with longer flowers
3. Disruptive Selection
 Favours individuals with _________________________-________________ traits over those with
intermediate variations
 Eg. Hummingbird population in a habitat with both short and long flowers, birds with longer and
shorter bills will be more successful
4. Sexual selection
 Favours the selection of any trait that influences the _______________ success of the individual
(usually male)
 Results in _____________________________ (striking differences between males and females)
Name: ________________________________
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Date: _______________________
Selection and Antibiotic Resistance
An example of Natural Selection in action can be found in the resurgence of __________________
TB is caused by rod shaped bacterium Mycobacterium tuberculosis
TB causes severe lung infections, cough and chest pain
___________________________, antibiotic, was developed for TB treatment
By 1970, TB had been almost completely wiped out
2006, there was an outbreak of TB in South Africa and by 2008 it spread to _____ countries
World Health Organization (WHO) reported that 1/3 of the population has TB and _____does not
respond of Streptomycin
How did this resistance occur?
Cumulative Selection
Evolution of a complex structure such as the eye is a cumulative process
Rare, beneficial mutations may be separated by ______________________________
Natural selection favors them and the adaptations they produce accumulate one by one
Cumulative selection is the accumulation of many _____________________ changes over long
periods of time and many generations, resulting in a significant new adaptation relative to the
_______________________________
Review Questions:
Suggest how large antlers or bright colouration could be a disadvantage for males of some species?
What is the difference between selective, disruptive and directional selection?