Evolution Mechanisms Quiz

Evolution Mechanisms

• Evolution is the change in the characteristics of a species over several generations.
• Natural selection is a key process in evolution.
• Individuals better adapted to their environment are more likely to survive and reproduce.
• They pass on their beneficial traits to the next generation, increasing the frequency of favorable alleles in the population.
• This process leads to gradual evolution of the species.
• Evolution depends on genetic variation in a population's physical characteristics.
• Some characteristics provide individuals with an advantage over others.
• These traits then get passed to the offspring.
• Evolution mechanisms include natural selection, gene flow, mutations, genetic drift, and non-random mating.

Natural Selection

• Natural selection affects variations in a population by favoring individuals best adapted to their environments.
• Better-adapted individuals survive, reproduce, and pass advantageous traits to their offspring.
• This increases the frequency of favorable alleles (traits) in successive generations.
• As a consequence, individuals suited to their environment thrive, leading to species evolution over time.
• Individuals with traits best suited to their environment, such as finding food, avoiding predators, and resisting disease, are more likely to survive, reproduce, and pass their genes on to their offspring.
• Nature "selects" the organisms best suited to thrive.
• Evolutionary effects include adaptations with survival and reproduction advantages.

Types of Natural Selection

• Directional selection: Favors individuals at one extreme of the trait distribution. The graph distribution leans toward one side, with improved traits. (Giraffes with longer necks reaching more leaves are an example)
• Disruptive selection: Favors individuals at both extremes of the trait distribution, with a minimum in the middle. Examples include squirrels with short tails for ground safety, and long tails for balance in trees, while mid-length tails provide no specific advantage.
• Stabilizing selection: Favors individuals near the center of the trait distribution. Traits near the middle of the distribution give the individual a better survival prospect, such as plants that are medium height for both light and wind resistance.

Gene Flow

• Also called "gene migration." Gene flow happens when migrating individuals breed in their new location.
• It's the movement of individuals or groups of individuals or species between populations.
• Gene flow also contributes to evolution by introducing or eliminating alleles from a population.

Mutations

• Mutations are changes in an organism's DNA.
• They are the starting point for new variations, influencing traits, behavior, and physiology in organisms.
• Mutations are inheritable changes in genotype that provide variation acted upon by natural selection.
• Mutations can be caused by DNA copying errors, external factors, or exposure to chemicals or radiation.
• Mutations are not always negative. For example, sickle cell anemia is a genetic disorder where red blood cells have abnormal shapes, causing fatigue and anemia. However, those who carry its trait have some genetic protection against malaria.
• Germ-line mutations affect gametes (sperm or eggs), potentially impacting the entire offspring.
• Somatic mutations appear in non-reproductive cells and are not passed on to future generations.

Genetic Drift

• Random changes in genetic frequencies within a population; it's random.
• Smaller populations are more vulnerable to genetic drift, potentially losing rare alleles due to chance events.
• Has drastic effects in small populations.
• Founder effect: A small group establishes a new population, and the new population's allele frequencies reflect those of the founders.
• Bottleneck effect: A large population experiences a drastic reduction in size (a "bottleneck"), and the remaining population's allele frequencies are different from the original.

Non-Random Mating

• Non-random mating is when the choice of mates is dependent on an organism's traits, not arbitrary.
• This can alter allele frequencies in a population.
• Hardy-Weinberg Principle: This principle models the equilibrium of genetic frequencies, stating that a population's genetic frequencies should stay the same unless factors influence it (e.g., non-random mating).
• Conditions for Hardy-Weinberg equilibrium include: random mating, large population size, no natural selection, no mutations, and no gene flow into or out of the population.