7.1-7.4
Unit 7 natural selection
7.1 introduction to natural selection
Evolution
A change in the genetic makeup of a population over generations.
Natural Selection
The process where heritable traits that improve survival or reproduction become more common in a population.
Population
A group of the same species living in the same area that can interbreed.
Adaptation
A heritable trait that increases fitness in a specific environment, or the process of becoming better suited.
Variation
Differences in traits among individuals within a population.
Heritability
The extent to which a trait is genetically passed from parents to offspring.
Differential Survival
When individuals with certain traits are more likely to survive under specific conditions.
Differential Reproduction
When individuals with certain traits leave more offspring than others.
Fitness
Reproductive success measured by the number of surviving offspring produced.
Selective Pressures
Environmental factors that favor some traits over others, shaping which individuals survive and reproduce.
Biotic
Living components of the environment that can act as selective pressures.
Abiotic
Nonliving environmental factors that influence survival and reproduction.
Environmental Stability
How constant or variable environmental conditions are over time.
Genetic Diversity
The variety of alleles and genotypes present in a population.
Genetic Variation
Differences in DNA and traits among individuals within a population.
Mutations
Random changes in DNA that can create new alleles and new traits.
Phenotype
An organism’s observable traits, influenced by genes and the environment.
Directional Selection
Selection that favors one extreme form of a trait.
Stabilizing Selection
Selection that favors the average trait and acts against extremes.
Disruptive Selection
Selection that favors both extremes of a trait over the intermediate form
7.2 Natural Selection
Natural Selection
A process where traits that help organisms survive and reproduce become more common in a population over generations.
Phenotypic Variation
Differences in observable traits (like color, size, or behavior) among individuals in a population.
Heritable Traits
Traits that are encoded by genes and can be passed from parents to offspring.
Fitness
How well an organism survives and produces viable offspring in a specific environment.
Mutations
Random changes in DNA that can create new alleles and new traits.
Genetic Recombination
The reshuffling of alleles during meiosis that creates new combinations in gametes.
Independent Assortment
The random distribution of different chromosome pairs into gametes during meiosis.
Random Fertilization
The chance pairing of one unique sperm with one unique egg to form a zygote.
Selective Pressure
An environmental factor that affects which traits help organisms survive and reproduce.
Peppered Moths
A classic example where moth color frequencies shifted with pollution levels on tree bark.
Sickle Cell Trait
The heterozygous condition for the sickle-cell allele that provides resistance to malaria with few or no symptoms.
Heterozygote Advantage
When individuals with two different alleles (heterozygous) have higher fitness than either homozygote.
Balanced Polymorphism
The stable maintenance of two or more alleles in a population due to selective forces.
DDT Resistance in Insects
An example where pesticide use selected for insects with resistance alleles, increasing their frequency rapidly.
Evolution
A change in trait or allele frequencies in a population over generations.
7.3 artificial selection
Artificial Selection
Human-directed breeding where people choose which organisms reproduce to increase desired traits.
Natural Selection
A process where environmental conditions favor individuals with heritable traits that boost survival and reproduction.
Genetic Diversity
The variety of alleles and genes present within a population.
Gene Pool
All the alleles for all genes in a population at a given time.
Genetic Bottlenecks
Sharp reductions in genetic diversity when only a few individuals contribute genes to future generations.
Convergent Evolution
Different lineages independently evolve similar traits because they face similar selective pressures.
Selective Pressures
Environmental factors that make some traits more beneficial than others, guiding which individuals survive and reproduce.
Phenotype
The observable traits of an organism, shaped by its genes and environment.
Fitness
An organism’s success at surviving and producing fertile offspring in a specific environment.
Common Ancestor
A past organism from which two or more species descended.
7.4 Population genetics
Population Genetics
The branch of evolution that tracks how allele frequencies change in populations over time.
Gene Pool
All the alleles present in a population at a given time.
Allele Frequencies
The proportions of different alleles in the gene pool.
Mutation
A random change in DNA that can create new alleles.
Point Mutations
Changes to a single base in DNA (such as silent, missense, or nonsense).
Chromosomal Mutations
Large-scale changes in chromosome structure, like deletions, duplications, inversions, or translocations.
Genetic Drift
Random changes in allele frequencies, strongest in small populations.
Bottleneck Effect
A sharp reduction in population size that reduces genetic diversity by chance.
Founder Effect
When a small group starts a new population with an allele mix that differs from the original population.
Gene Flow
Movement of alleles between populations through the migration of organisms or gametes.
Population Size
The number of individuals in a population, which affects how strongly chance processes act.
Natural Selection
The non-random process where alleles that improve fitness become more common.
Speciation
The formation of new species when populations diverge enough to stop interbreeding.