Hardy-Weinberg Principle Quiz

Hardy-Weinberg Principle

• Specifies conditions where allele and genotype frequencies in a population remain constant over generations (no evolution)
• Five conditions for no evolution: No mutations, No gene flow, Random mating, No genetic drift, No natural selection
• Allele frequencies can be calculated if the frequencies of genotypes are known.
• The Hardy-Weinberg principle can be used to determine if a population is evolving.
• If allele frequencies change, evolution is occurring.

Hardy-Weinberg Example

• In a population, 6 out of 20 individuals have attached earlobes (ee)
• Frequency of the ee genotype: 6/20 = 0.3
• Frequency of EE genotype: 0.45^2= 0.2025 ~0.2
• Frequency of Ee genotype: 2*(0.45)*(0.55) = 0.495
• Frequency of unattached earlobes: 1 - 0.3=0.7
• Frequency of recessive allele (e): √0.3 = 0.55
• Frequency of dominant allele (E): 1 - 0.55 =0.45

Altering a Gene Pool

• Natural selection
• Genetic drift (Bottleneck effect, Founder effect)
• Gene flow (immigration/emigration)
• Mutations
• Non-random mating

Genetic Drift

• Random fluctuations in allele frequencies, especially pronounced in small populations
• Bottleneck effect: A drastic reduction in population size due to a sudden event (natural disaster, hunting). The surviving population may have a different allele frequency than the original population
• Founder effect: A small group from a larger population colonizes a new area. The new population has a different allele frequency from the original.

Speciation

• Allopatric: Geographic isolation leads to speciation. A population is separated by a geographic barrier (mountain range, river), causing divergence.
• Sympatric: Speciation occurs within a population without geographic isolation through changes in niche, or mating behaviors.

Geographic Isolation

• A physical barrier prevents gene flow between populations, driving divergence.
• Examples: Mountains, canyons, glaciers, rising sea levels.

Reproductive Isolation

• Prevents interbreeding between species, maintaining separate gene pools.
• Four ways reproductive isolation occurs: Geographic isolation, niche differentiation, behavioral isolation, and altered physiology

Punctuated Equilibrium vs. Gradualism

• Punctuated equilibrium: Evolution occurs in bursts of rapid change followed by long periods of little or no change.
• Gradualism: Evolution occurs in slow, steady changes over long periods of time

Genetic Variation

• Essential for the survival of a species and for evolution to occur.
• Genetic variation allows organisms in a population to respond to environmental changes, with variations in traits.

Analogous vs. Homologous

• Analogous structures: Structures in different species that are similar in function but not in evolutionary origin (e.g., wings of birds and insects).
• Homologous structures: Structures that have similar evolutionary origins and structure but may have different functions in different species (e.g., forelimbs of humans, cats, and bats).

Convergent vs. Divergent Evolution

• Convergent: Different species evolve similar traits due to similar environmental pressures (e.g., wings in birds and bats)
• Divergent: Species evolve different traits from a common ancestor due to different environmental conditions (e.g., the forelimbs of mammals).