SELECTION

Genotype: Genetic makeup of an organism.
Phenotype: Observable traits of an organism determined by genotype and environment.
Connection between genotype and phenotype affects the gene pool, which is defined as the total collection of genes in a population.

Natural selection is a key mechanism that changes a gene pool by favoring certain traits that enhance survival and reproduction.
Natural Selection: The process by which individuals with favorable traits reproduce more successfully than others.
Practice calculations related to the Hardy-Weinberg Principle in class to predict changes in the gene pool.

Used to determine if a population is evolving.
Equations allow predictions about genotype frequencies in a population under ideal conditions (absence of evolution).
Key purpose: To answer the question "Is this population evolving?".

Evolution: Change in genetic composition of populations over time, leading to change in gene pools.
Observed across various settings: laboratory, natural populations, and fossil records.
Underlies biodiversity, responsible for all species that have ever existed on Earth.

While natural selection is the most significant, other mechanisms include:
- Sexual Selection: Preferences for certain traits in mates.
- Genetic Drift: Random changes in allele frequencies, especially in small populations.
- Mutation: Introduction of new genetic variations.
- Migration: Movement of individuals between populations, affecting allele frequencies.

Fertility Observations: Most populations exhibit potential for exponential growth; however, they remain stable, indicating a limiting factor.
Differential Reproductive Success: Some individuals reproduce more successfully due to varying traits, leading to a balance in population numbers.
Resource Limitation: Resources (food, space) remain constant in stable environments, limiting population growth.
Variability in Traits: Individuals in a population show variability in traits (phenotypic differences) that can influence survival and reproduce rates.
Heritability of Traits: Traits that confer survival advantages can be inherited, leading to gradual evolutionary changes in the population.

Over generations, as resources remain constant, the traits making individuals more suited to their environment become more prevalent in the gene pool.
Fitness: Refers to an individual's suitability for its environment, not physical fitness.
Natural selection results in an increase in the frequency of beneficial traits over generations.

Color Morphs of Red-Backed Salamander: Different morphs (solid red vs. brown with stripes) are genetically determined.
Predation Pressure: Predators show preference for certain morphs, leading to differential survival rates (e.g., more red individuals survive).
Hypothesis generation about future genetic shifts in response to natural selection based on coloration preferences.

Alleles: Different forms of a gene; variations created through mutations.
Genotypes represent combinations of alleles that determine phenotypes (e.g., SS for striped salamanders, RR for red).
Natural selection acts on phenotypes rather than genotypes; only certain phenotypes are favored by external pressures.

A null hypothesis helps establish a comparison between observed data and what would occur in the absence of selection.
Conditions for the null hypothesis:
- Large, stable breeding population (no genetic drift).
- Random mating (no sexual selection).
- No mutations occurring.
- No migration affecting allele frequencies.

Hardy-Weinberg equations help state expected genotype frequencies under the assumption of no evolution:
- Let p = frequency of dominant allele,
- q = frequency of recessive allele,
- Condition: $(p + q = 1)$ .

The process to calculate p and q involves counts of homozygous and heterozygous individuals in sampled populations.
Total alleles counted in the population helps establish frequencies to predict genotype distributions under Hardy-Weinberg conditions.

By counting observed genotypes and applying Hardy-Weinberg formulas, researchers can develop predictions about expected genotype proportions in populations.
Comparing expected versus observed frequencies helps assess whether evolutionary changes (via selection pressures) are in effect.
Understanding the implications: if observed data deviate from expected frequencies, evolution via selection is likely occurring.