Selection Revision Notes

Within a population, genetic diversity means individuals have different traits due to variations in their genes. Organisms often produce more offspring than the environment can support, ensuring some survive despite challenges. This overproduction leads to competition for limited resources such as food, water, and shelter.

• Genetic diversity provides a range of traits.
• Many offspring are produced to increase survival chances.
• Resources are limited, causing competition.
• Not all offspring survive to adulthood.

Because resources are limited, individuals compete to survive. Those with traits better suited to their environment have a higher chance of surviving. This competition drives natural selection, where only the fittest individuals survive and reproduce.

• Limited resources cause competition.
• Better-suited individuals survive more often.
• Natural selection favors advantageous traits.
• Survival depends on adaptation to environment.

Individuals that survive due to advantageous traits are more likely to reproduce and pass these traits (alleles) to their offspring. Over many generations, this process changes the genetic makeup of the population, leading to evolution.

• Advantageous traits increase reproductive success.
• Alleles of successful individuals are inherited.
• Population genetics change over time.
• Natural selection drives evolution.

Humans begin selective breeding by identifying individuals that have traits beneficial for survival, productivity, or appearance.

These traits might include higher yield, disease resistance, or faster growth.

Only these individuals are selected to reproduce, ensuring the traits are passed on.

• Select individuals with favorable characteristics.
• Traits can be physical, behavioral, or physiological.
• Selection is intentional and controlled by humans.

The chosen individuals are mated to produce offspring.

This controlled mating increases the chance that offspring inherit the desired traits.

The process can involve plants or animals depending on the breeding program.

• Mating is controlled to combine desired traits.
• Offspring inherit traits from selected parents.
• Breeding can be repeated over generations.

Offspring are evaluated for the presence and strength of the desired traits.

Only those showing the best expression of these traits are selected to breed the next generation.

This cycle is repeated to enhance the traits in the population over time.

• Evaluate offspring traits carefully.
• Select best offspring for next breeding cycle.
• Repeat process to strengthen traits over generations.

Humans select parent plants or animals with traits they want to enhance, such as higher yield or better quality.

These parents are bred together to produce offspring.

From the offspring, those showing the desired traits most strongly are selected for further breeding.

This cycle is repeated over many generations to strengthen the traits in the population.

• Select parents with desirable traits.
• Breed selected parents to produce offspring.
• Choose offspring with best traits for next breeding.
• Repeat over generations to enhance traits.

In crop plants, farmers may select wheat plants that produce higher yields and breed them to improve food production.

In domesticated animals, farmers may breed cows that produce more milk to increase dairy output.

Over time, these practices lead to populations with improved characteristics beneficial to humans.

• Wheat bred for higher yield.
• Cows bred for increased milk production.
• Traits become stronger and more common over generations.

Repeating the selection and breeding process over multiple generations is essential to fix the desired traits in the population.

Without repetition, traits may not become stable or widespread.

This controlled process differs from natural selection because humans direct which traits are favored.

• Multiple generations needed to enhance traits.
• Consistent selection ensures trait stability.
• Process is artificial and human-directed.

Within any population, individuals show differences in their traits due to genetic variation. Some of these traits give certain individuals an advantage in surviving and reproducing in their environment. For example, a beetle with a shell color that camouflages it better from predators is more likely to survive.

• Genetic variation exists among individuals in a population.
• Some traits improve chances of survival and reproduction.
• Individuals with advantageous traits are more likely to survive.

Natural selection is the process where individuals with beneficial traits survive longer and reproduce more than others. These individuals pass their advantageous traits to their offspring. Over many generations, these traits become more common in the population, leading to adaptation.

• Natural selection favors individuals with beneficial traits.
• These individuals reproduce and pass on their traits.
• Frequency of advantageous traits increases over generations.

As natural selection continues over many generations, the population as a whole becomes better suited to its environment. This improved suitability is called adaptation. It enhances the population's overall fitness, increasing its chances of survival and reproduction in the environment.

• Adaptation is a population-level change over time.
• Populations become better suited to their environment.
• Adaptation increases survival and reproductive success.

Bacteria can have random mutations in their DNA. Some mutations may give bacteria the ability to survive antibiotics that would normally kill them. These resistant bacteria survive antibiotic treatment while others die.

• Mutations create genetic variation in bacteria.
• Some mutations confer antibiotic resistance.
• Resistant bacteria survive antibiotic exposure.

When antibiotics are used, they kill susceptible bacteria but not resistant ones. This creates a selective pressure where resistant bacteria have a survival advantage. They face less competition and can reproduce more.

• Antibiotics kill non-resistant bacteria.
• Resistant bacteria survive and reproduce.
• Selective pressure increases frequency of resistance genes.

As resistant bacteria reproduce, they pass resistance genes to their offspring. Over many generations, the population becomes dominated by resistant strains, making infections harder to treat.

• Resistance genes are inherited by offspring.
• Population shifts toward resistant bacteria.
• Misuse of antibiotics accelerates resistance development.

Natural selection is a natural process where organisms with traits better suited to their environment survive and reproduce more successfully. It is driven by environmental factors and happens without human involvement.

• Occurs naturally without human control.
• Driven by environmental pressures.
• Favors traits that improve survival and reproduction.

Artificial selection is a human-controlled process where individuals with desired traits are bred to produce offspring with those traits. It is intentional and aims to enhance characteristics beneficial or attractive to humans.

• Controlled by humans selecting traits.
• Used to produce desired characteristics.
• Common in agriculture and animal breeding.

Both processes change populations over generations by increasing certain traits. However, natural selection adapts populations to their environment, while artificial selection focuses on traits useful or desirable to humans.

• Both cause changes in populations over time.
• Natural selection adapts to environment.
• Artificial selection targets human-preferred traits.