BIOEE 1780 Lecture Notes - Lecture 3: Selective Breeding, Flowchart, Heritability

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Lecture 3 Natural Selection I
Genetic Drift: evolution that occurs due to random changes in the genetic composition of a population
from one generation to the next
Due to chance
Ecological Character Displacement: natural selection pushes the phenotypes of two species in opposite
directions when they live in the same area and compete for the same resource
When 2 species overlap, individuals that are similar to the other species will experience intense
competition. Individuals that are least similar to the other species experience less competition and
have more reproductive success.
The two populations diverge as a result.
Artificial Selection: results from human activity; breeders non-randomly choose individuals with
favorable traits to use as breeding stock, imposing a selection for those traits
Example: artificial selection in purebred dogs
o Humans provide a relaxation of selective pressures
o Transition from function to form
Breed standards led to strong artificial selection
Developed in the mid 1800s
Caused the gene pool to close
All organisms must do three things due to selective pressures:
Protection from illness/injury
Finding food
Getting a mate
Darwin's Three Postulates - Remember these, don't need to memorize flowchart above
1. Individuals are variable in some trait(s)
2. At least some of this variation is heritable
3. There is a struggle for survival or reproduction, and some individuals fare better than others
Selection operates on many variable traits:
Morphological traits (ex. appearances)
Physiological traits (ex. cold tolerance, digesting certain foods)
Behavioral traits (ex. altruism, social abilities)
What causes phenotypic variation?
Genetic differences (ex. dog breeds)
Environmental differences (ex. plants grown in different conditions)
Interactions between genes and the environment
Other reasons we might see variation in a population:
Measurement error
Ontogenetic differences: variation in phenotype across development; occurs mostly before sexual
maturation
Heritability: the proportion of within-population variation in a trait that comes from genetic factors
Can be measured via a graph of average parent trait vs. average offspring trait
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Document Summary

Genetic drift: evolution that occurs due to random changes in the genetic composition of a population from one generation to the next: due to chance. Individuals that are least similar to the other species experience less competition and have more reproductive success. All organisms must do three things due to selective pressures: protection from illness/injury, getting a mate. Darwin"s three postulates - remember these, don"t need to memorize flowchart above: at least some of this variation is heritable, there is a struggle for survival or reproduction, and some individuals fare better than others. Selection operates on many variable traits: morphological traits (ex. appearances, physiological traits (ex. cold tolerance, digesting certain foods, behavioral traits (ex. altruism, social abilities) What causes phenotypic variation: genetic differences (ex. dog breeds, environmental differences (ex. plants grown in different conditions) Other reasons we might see variation in a population: measurement error, ontogenetic differences: variation in phenotype across development; occurs mostly before sexual.

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