48 Questions
What is the result of the diploid chromosome number in a new species formed from two parent species?
The diploid chromosome number is equal to the sum of the two parent species
What is the primary reproductive barrier that keeps the gene pools of two species separate in Lake Victoria cichlids?
Mate choice based on male breeding coloration
What is the term for geographic regions where members of different species meet and mate, producing at least some offspring of mixed ancestry?
Hybrid zones
What is the process by which individuals with certain inherited characteristics are more likely to obtain mates?
Sexual selection
What is the term coined by Stephen Jay Gould and Niles Eldredge to describe the pattern of sudden change punctuated by periods of apparent stasis?
Punctuated equilibria
What is the primary mechanism driving sympatric speciation in the case of the Lake Victoria cichlids?
Mate choice based on male breeding coloration
What is the primary function of prezygotic barriers in reproductive isolation?
To impede mating between species or hinder fertilization
Which type of reproductive barrier is responsible for preventing mating between two species that occupy the same geographic area but have different habitat preferences?
Habitat isolation
What is the result of reduced hybrid fertility in postzygotic reproductive barriers?
Hybrid offspring are sterile
Which type of speciation is likely to occur when two species are geographically separated from each other?
Allopatric speciation
What is the primary function of gametic isolation in reproductive isolation?
To prevent fertilization of eggs by sperm of another species
What is the outcome of hybrid breakdown in postzygotic reproductive barriers?
Hybrid offspring are unable to survive to adulthood
What is the primary mechanism that prevents complete mating between different species of snails?
Differing directions of their shells
What is the outcome of hybrid offspring between a donkey and a horse?
Viable but sterile offspring
Which type of speciation does not require geographic separation?
Sympatric speciation
What is the result of gene flow interruption in a population?
Speciation
Why are some hybrid offspring between different species of salamanders frail or do not complete development?
Genetic incompatibility of parent species
What is the purpose of understanding reproductive isolation in the context of speciation?
To understand the concept of speciation
What type of polyploidy occurs when an individual of a single species has more than two sets of chromosomes?
Autopolyploidy
What is the primary outcome of reinforcement in a hybrid zone?
Hybridization decreases, resulting in weaker hybrids
What is the likely mechanism of speciation responsible for the evolution of five anole species in Puerto Rico?
Allopatric speciation
What is the term for the process of speciation that occurs over long periods of time, as implied by the Darwinian process of descent with modification?
Gradualism
What is the result of intersexual selection in the case of female desert funnel web spiders from canyons?
Avoiding mating with aggressive dry land males
What is the outcome of stability in a hybrid zone?
Hybrids continue to be produced
What is the primary characteristic of a biological species according to the biological species concept?
A group of populations whose members have the potential to interbreed and produce viable, fertile offspring
What is the primary role of gene flow in the context of speciation?
To maintain the gene pool of a species together
Which type of reproductive barriers prevent the hybrid from developing into a viable, fertile adult?
Postzygotic reproductive barriers
What is the primary distinction between allopatric and sympatric speciation?
The presence or absence of geographical barriers
What is the term for the pattern of sudden change punctuated by periods of apparent stasis?
Punctuated equilibrium
What is the primary consequence of hybrid zones following the direction of reinforcement?
Strengthening of postzygotic reproductive barriers
Which of the following concepts views a species in terms of its structural features?
Morphological species concept
What is the primary reason why the biological species concept cannot be applied to fossils?
Fossils do not exhibit gene flow
Which of the following is an example of allopatric speciation?
Ammospermophilus antelope squirrels
What is the outcome of reduced hybrid viability in postzygotic reproductive barriers?
Hybrids die during embryonic development
Which of the following species concepts defines a species as the smallest group of individuals on a phylogenetic tree?
Phylogenetic species concept
What is the primary mechanism driving the formation of separate species in the case of the Ammospermophilus antelope squirrels?
Geographic barrier
What is the primary mechanism by which sexual reproduction increases genetic variation in a population?
Genetic recombination and the shuffling of alleles
What is the term for the duplication of chromosome sets, which can introduce new genetic variation in plants?
Polyploidy
What is the primary mechanism by which frequency-dependent selection favors certain phenotypes and preserves genetic variation?
The fitness of an allele depends on its frequency in the population
What is the primary consequence of heterozygote advantage in a population?
Preservation of genetic variation
What is the primary mechanism by which neutral variation preserves genetic diversity in a population?
The alleles are not subject to natural selection
What is the primary example of frequency-dependent selection in the text?
The fish guarding their scales from predators
What is the primary role of natural selection in the evolution of a population?
To reduce variation in a population by eliminating unfavorable traits
Which of the following is NOT a source of genetic variation in a population?
Genetic recombination during asexual reproduction
What is the result of increased genetic variation in a population?
Enhanced ability to evolve and adapt to changing environments
How can genetic recombination during sexual reproduction increase genetic variation?
By shuffling alleles and creating new combinations
What is an example of genetic variation observed in different populations of the same species?
Different body sizes in different geographic locations
Why is genetic variation essential for evolution to occur?
Because it provides the raw material for natural selection to act upon
Study Notes
Speciation
- The new species has a diploid chromosome number equal to the sum of the diploid chromosome numbers of the two parent species.
Sexual Selection
- In sexual selection, individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
- Mate choice based on male breeding coloration is the main reproductive barrier that normally keeps the gene pools of two species separate.
Hybrid Zones
- Hybrid zones are geographic regions in which members of different species meet and mate, producing at least some offspring of mixed ancestry.
- In hybrid zones, there are three possible outcomes: Reinforcement (hybridization decreases), Fusion (gene flow leads to two species becoming one), and Stability (hybrids continue to be produced).
Speciation Patterns
- Punctuated equilibria refers to the periods of apparent stasis punctuated by sudden change.
- Speciation can occur rapidly or slowly, and it can result from changes in few or many genes.
Reproductive Barriers
- Prezygotic reproductive barriers:
- Habitat isolation: Two species that occupy different habitats within the same area may encounter each other rarely.
- Temporal isolation: Species that breed during different times of the day, different seasons, or different years cannot mix their gametes.
- Behavioral isolation: Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers.
- Mechanical isolation: Morphological differences prevent successful mating.
- Gametic isolation: Sperm of one species may not be able to fertilize the eggs of another species.
- Postzygotic reproductive barriers:
- Reduced hybrid viability: Hybrid offspring may not complete development or are frail.
- Reduced hybrid fertility: Hybrids are strong but sterile.
- Hybrid break down: Hybrids are fertile but the 2nd generation is sterile.
Speciation Mechanisms
- Allopatric speciation: Two species may form when a geographic barrier interrupts gene flow between two populations.
- Sympatric speciation: This occurs within populations with overlapping boundaries.
- Polyploidy: The duplication of chromosome sets can introduce new genetic variation in plants.
Biological Species Concept
- The biological species concept states that a species is a group of populations whose members have the potential to interbreed and produce viable, fertile offspring.
- However, they do not breed successfully with other populations.
- Gene flow is what maintains the gene pool of a species together.
- Limitations of the biological species concept:
- Cannot be applied to fossils or asexual organisms (including all prokaryotes).
- Emphasizes absence of gene flow, but gene flow can occur between distinct species.
Test your knowledge about the unique characteristics that prevent different species from interbreeding. From spotted skunks to blue-footed boobies, learn about the fascinating ways in which species ensure reproductive isolation. Explore the differences in snail shells, sea urchins, and plant stigmas that keep species distinct.
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