Natural Selection Flashcards
Natural Selection
The process where organisms better adapted to their environment tend to survive and produce more offspring, reducing variation
Darwin’s Theory
Individuals in a species show wide range of variation
For a trait to be subject to natural selection it must be heritable
Most organisms produce more offspring than the environment can realistically support which approaches the carrying capacity of the environment
As more offspring are produced there are less resources available due to sheer amount of individuals in population which will lead to increased competition, predation and disease
Survival of the fittest will happen where individuals with features most suited or adapted to the environment are more likely to survive and reproduce and pass their alleles to the next generation
The alleles for the advantageous characteristic become more frequent in the population which evolves the species and changes the population as a whole
Mutation VS Sexual Reproduction
Change in DNA Sequence
Combining genetic material from 2 parents
Source of new alleles
Source of new combinations from existing alleles
Source is DNA Rep errors and environmental factors
Source is meiosis and fertilization
Heritable if in germline cells
Heritable
Generally random
Random combination of parental genes
Carrying Capacity and Examples
The maximum number of individuals of a particular species that the environment can sustainably support
Food availability
Water availability
Space
Mates
Nutrients
Sunlight
Shelter
Sexual Selection
Type of natural selection where selective pressure is related to attracting mates
Intersexual Selection involves individuals of one sex choosing mates of the other sex based on certain preferences (physical or behavioural or overall fitness)
Intrasexual Selection involves competition within one sex to access mates (physical combat or less direct forms of competition)
Sexual Selection Evolution of Traits
Ornamentation: Bright colors and remarkable displays
Larger size or greater strength is advantageous in intrasexual competition
Elaborate songs and dances used to attract mates
Gene Pool
All the genes and their different alleles present within a population
Large gene pool indicates greater genetic diversity, and changes in gene pool over time drive evolution
Allele Frequency
The proportion of one allele of one organism in a population
Changes to Allele Frequency Processes
Mutation: A random unpredictable change in the DNA base sequence
Gene Flow: Movement of alleles into or out of population as a result of immigration and emigration
Nonrandom mating: Choice of mate is dependent on particular genotype or phenotype which means less gene flow
Natural Selection: Individual organisms possess favorable traits that are more likely to survive and reproduce
Genetic Drift: Occurs by chance and is wiping out majority of alleles, where the smaller the population the greater the impact will have. If it’s strong enough the allele might be completely removed from the population
Neo-Darwinism and Emphasizations
Scientists integrating Darwin’s theory with newly developed field of genetics
Genes are the units of heredity
Mutations are the source of variation
Natural selection acts on genes
Evolution is a change in allele frequency
Stabilizing Selection
Occurs when selective pressures remain the same for a long time
Against the two extremes of a trait with the resulting bell-shaped curve being narrower, and does not promote evolutionary change
Favors individuals with a general phenotype
Directional Selection
Occurs when there are gradual changes in environmental conditions
Favors one extreme of a range of characteristics and against the other
Allele frequency results in bell shaped curve shifted in direction of selection, and brings about an evolutionary change
Disruptive (Diverging) Selection
Occurs when an environment change may produce selection pressures that favor two extremes of a characteristic resulting in two different phenotypes
Favors extreme phenotypes and against general intermediate phenotypes
Hardy Weinberg Equation
p + q = 1
p^2 + 2pq + q^2 = 1
