Evolution and Natural Selection Review

Artificial Selection: Human intervention in breeding for specific traits. Used in agricultural crops, livestock, and pets.
Analogous Structures: Structural features in different organisms that serve similar functions but have evolved separately; they are not derived from a common ancestor.
Vestigial Structures: Anatomical features that have lost most or all of their original function in a species through evolution.
Homologous Structures: Structures in different species that are similar due to shared ancestry, even if they have different functions.
Natural Selection: The process by which organisms better adapted to their environment tend to survive and produce more offspring.
Match Terms with Images: The task involves pairing terms like analogous and homologous structures with the right visual representation to illustrate their differences.

Convergent Evolution: This occurs when organisms from different evolutionary backgrounds develop similar traits due to similar environmental pressures.
- Example: Two different mutations leading to the same phenotype.
- Analogous Structures as a result of convergent evolution: same function but different structure (e.g., wings of bats and insects).
Divergent Evolution: The process in which two or more related species become more dissimilar, usually due to different environments or selective pressures.
- Example: Different species developed from a common ancestor; could include vestigial structures resulting from divergent evolution.

Directional Selection: This type shifts the mean trait value in a population toward one extreme, favoring one end of the phenotypic spectrum.
- Outcome: A specific trait may become more common over generations.
Disruptive Selection: Selection against the median trait values, favoring the extremes. This can lead to two distinct populations if extreme phenotypes are advantageous.
Stabilizing Selection: Selection that favors the average phenotype in a population, leading to a decrease in variation. Extreme traits are selected against.

Example 1: Snails on colored rocks in a stream.
- Rocks are black or white. Snails are a color gradient (black to gray to white).
- Predation by a fish that can camouflage with matching rocks implicates disruptive selection, as gray snails are easily seen and less likely to survive.
Example 2: Guppies in a lake in South Africa.
- Larger guppies face higher predation by pike fish.
- Suggests directional selection favoring smaller guppies that can escape better.
Example 3: Starlings produce an average of five eggs per clutch.
- If more than five, parents cannot feed adequately; if fewer, the clutch may be entirely predated.
- Indicates stabilizing selection for the clutch size of five eggs.

Speciation: The evolutionary process in which new biological species arise.
Biological Species Concept: Defines species based on the ability of members to interbreed and produce viable, fertile offspring. Reproductive isolation is key.
Hybrids: Offspring from different species that may be fertile or infertile and can contribute new genetic material to a population.

Prezygotic Barriers: Prevent mating or fertilization.
- Types: Habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation.
Postzygotic Barriers: Occur after fertilization.
- Types: Reduced hybrid viability, reduced hybrid fertility, hybrid breakdown (hybrids may be sterile or their offspring may not survive).

Populations: The smallest unit that can evolve, groups of individuals of the same species living in a specific area that interbreed.
Evolution: Change in allele frequencies within a population's gene pool over time.
Gene Pool: The total collection of alleles in a population.

Mutations: Random alterations in DNA that can create new alleles.
Natural Selection: Non-random survival based on advantageous traits.
Non-random Mating: Selection for particular traits during mating which affects allele frequencies.
Migration (Gene Flow): Introduction or removal of alleles through movement of organisms into and out of populations.
Genetic Drift: Random changes in allele frequencies, more impactful in smaller populations.

Founder Effect: When a new population is started by a small number of individuals from a larger population, leading to reduced genetic variation.
Bottleneck Effect: A significant reduction in population size due to environmental events, leading to changes in allele frequencies.

Concept: A principle stating that allele frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences. Conditions for equilibrium require no mutation, migration, selection, or random mating.
- Equation: p^2 + 2pq + q^2 = 1 where:
- p = frequency of the dominant allele
- q = frequency of the recessive allele
- p^2 = frequency of homozygous dominant genotype
- 2pq = frequency of heterozygous genotype
- q^2 = frequency of homozygous recessive genotype.

Example Problem 1: Given a frequency of the dominant allele A (p) at 0.67, calculate the recessive allele frequency (q), the frequencies of genotypes.
Calculation: Using Hardy-Weinberg formulas to solve for genotypic frequencies:
- q = 1 - p
- p^2 ext{ (homozygous dominant) = } p imes p
- 2pq ext{ (heterozygous) = } 2 imes p imes q
- q^2 ext{ (homozygous recessive) = } q imes q
Example Problem 2: If 36% of butterflies exhibit white wings (bb), determine frequencies of genotypes (homozygous recessive, homozygous dominant, heterozygous) and allele frequencies in a population of 1308 butterflies.

Important Note: Understanding these principles and mechanisms is crucial for studying evolution and population genetics.
Next Assignment: Prepare for Hardy-Weinberg Koi Fish Simulation and Phylogenetics Edpuzzle due after Spring Break.