A change in allele frequencies in a population from generation to generation
A unit of DNA (stretch of nucleotides) that codes for a protein; unit of heredity
Alternate forms of the same gene; different alleles may code for different phenotypes
The set of observable physical characteristic of an organism; product of genes and the environmnet
An individual's set of genes; the pair of alleles an organism has for a gene
Characteristic passed from parent to offspring via genes
- A permanent change in an organism's DNA sequence that may or may not result in phenotypic change
- Occurs randomly
- Ultimate source of all genetic variation
- Think percent
- How common an allele is in a population relative to the other alleles for that gene
Set of individuals of a species that live in the same area and interbreed
Evolution Inferences: Survival
- Differential survival among phenotypes.
- Certain phenotypes will have a better survival rate
Evolution Inferences: Reproduction
- Survivors reproduce while non-survivors don't (differential reproduction)
- Survivors pass on genes to the next generation
Evolution Inferences: Response to Environment Pressure
Individuals with phenotypes better suited to the environment survive and reproduce
Evolution Inferences: Variation
Pre-existing variation needed for population response to environmental change
Evolution by Natural Selection Inferences
- Survival and reproduction differ among varied phenotypes in response to an environmental pressure
- Individuals with phenotypes better suited to the environment pass their alleles to offspring at a greater rate than individuals with phenotypes poorly suited to their environment
- Alleles for adaptive phenotype well suited to the current environment more common in the population in the next generation.
If beak size for a bird species is determined by which foods nestlings eat most frequently during their early development and is not an inherited trait, would the population evolve in response to the drought?
- No-- It not inherited so the phenotype is determined by the environment not by the alleles
- Evolution can only happen for traits determined by genes (alleles)
What is the only way populations can evolve?
- Populations can only evolve regarding traits that are inherited (passed from parents to offspring)
- Use caution when identifying traits as product of adaptive evolution-- situation must meet criteria needed for natural selection to occur
Evolution via Genetic Drift Observations
- Random occurrences can result in evolution of populations
- These populations are not better suited to their environment
Evolution via Genetic Drift Inferences
- Evolution is not always predictable
- Evolutions does not always result in better adapted populations
- Evolution can happen via multiple mechanisms
Evolution via Genetic Drift
When evolution is caused from random change
Barring the introduction of new alleles (no mutations) into the population, can this population evolve?
- Allele frequencies can't change if 100% of the population has the same allele
- Evolution works on preexisting variation in a population
A predator is introduced to the island. The birds' non-camo color and large tails make them easy to catch.
How will the population likely respond to the introduction of the predator?
- The population will likely die out or decline precipitously.
- This is because mutations are random. Organisms don't mutate or adapt because they "need" to.
Evolution via Migration
Evolution can occur via migration, or gene flow, as new alleles are introduced to a population
New birds are added to the forest that are better adapted for the new predator.
Will evolution as a result of gene flow result in a better adapted population?
- No, the green bird came to the island by random.
- The gene flow adds alleles irrespective of environmental pressures
In the green bird introduction example, if alleles introduced via gene flow become more common in future generations because of differential survival/reproduction under an environmental pressure.
What evolution mechanism is at work?
- Natural selection.
- Several mechanisms of evolution can be at work at the same time.
- The ultimate source of all genetic variation
- By default, introducing a new allele changes allele frequencies
Four mechanisms of Evolution
- Natural Selection
- Gene Flow
- Genetic Drift
Adaptive (non-random) evolution
Natural selection- individuals with certain inherited traits survive/reproduce more than other individuals as their traits make them better suited to their environment
Non-adaptive (random) evolution
- Mutation- change in DNA sequence
- Gene Flow- movement of alleles from one population to another
- Genetic Drift- random events change allele frequency from generation to generation