Questions and Answers
How many named plant species are on earth?
250K
How many named animal species are on earth?
1M
How many vertebrates are there?
51K
How many species are there?
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Species may differ in which of the following?
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What is sexual dimorphism?
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What are reproductive barriers?
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What does prezygotic mean?
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What does postzygotic mean?
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What are the five prezygotic reproductive barriers?
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What is the difference between habitat isolation and temporal isolation?
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What is the difference between behavioral isolation and mechanical isolation?
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What happens during gametic isolation in external and internal fertilization?
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What are the three postzygotic reproductive barriers?
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What is the difference between reduced hybrid viability and reduced hybrid fertility?
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Why is the hybrid offspring usually sterile?
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What happens during hybrid breakdown in the first and second generation of offspring?
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What are the issues with the biological species concept?
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What is an example of a viable hybrid?
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What are the two basic patterns of speciation?
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What is an example of anagenesis?
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What is an example of cladogenesis?
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What are the two basic patterns of cladogenesis?
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What is the difference between allopatric and sympatric speciation?
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How do populations become geographically isolated via allopatric speciation?
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What type of biological factors cause reproductive isolation of populations living in the same area (cladogenesis via sympatric speciation)?
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What happens during genetic incompatibility via autopolyploidy?
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What is an example of a sexual selection barrier?
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What is the result of the study from figure 24.12?
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What is the conclusion of the study in figure 24.12?
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What type of breakdown of reproductive barriers is shown in figure 24.16?
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Study Notes
Species Count on Earth
- Approximately 250,000 named plant species exist globally.
- Roughly 1 million named animal species have been identified.
- Vertebrates account for about 51,000 species.
- Overall, around 1.75 million species have been described to date.
Species Variation
- Species can vary in morphology, physiology, behavior, and DNA sequence.
Sexual Dimorphism
- Males and females of certain species exhibit significant physical differences, exemplified by the red male parrot and green female parrot.
Reproductive Barriers
- Reproductive barriers prevent successful breeding between organisms and are categorized into prezygotic and postzygotic types.
Prezygotic Barriers
- Prezygotic barriers impede mating and fertilization, preventing zygotes from forming.
- Five types include:
- Habitat isolation: Species live in the same area but in different habitats.
- Temporal isolation: Species breed at different times (day/season/year).
- Behavioral isolation: Specific behaviors attract mates.
- Mechanical isolation: Anatomical differences prevent sperm transfer.
- Gametic isolation: Gametes fail to recognize each other during fertilization.
Postzygotic Barriers
- Postzygotic barriers occur after fertilization and prevent hybrid zygotes from developing into fertile adults. They include:
- Reduced hybrid viability: Hybrid embryos die early.
- Reduced hybrid fertility: Offspring are usually sterile despite being healthy.
- Hybrid breakdown: First-generation hybrids can be fertile; second-generation hybrids are typically weak or sterile.
Biological Species Concept Issues
- Infertility assessment can be challenging.
- The concept does not apply to asexually reproducing or extinct species.
- Some viable hybrids can exist, such as ligers.
Patterns of Speciation
- Two primary patterns:
- Anagenesis: Evolution within a single lineage, exemplified by the increased brain size of ancestral humans.
- Cladogenesis: Lineage splitting, as seen with the evolution of birds from reptile ancestors.
Types of Cladogenesis
- Cladogenesis includes:
- Allopatric speciation: Geographic separation leads to restricted dispersal and gene flow between populations.
- Sympatric speciation: Biological factors limit gene flow between populations in the same area.
Geographic Isolation Mechanisms
- Geographic isolation in allopatric speciation can occur through:
- Extinction of connecting populations.
- Colonization of new, remote geographical areas.
- Geological processes that create barriers.
Biological Factors in Sympatric Speciation
- Genetic incompatibility, such as polyploidy, and sexual selection (e.g., female preference) can cause reproductive isolation.
Genetic Incompatibility via Autopolyploidy
- Autopolyploidy results from the failure of cell division after chromosome duplication, leading to tetraploid individuals.
- Tetraploids can be viable and fertile, while hybrids between tetraploids and diploids may be triploid and usually sterile.
Study Figures and Results
- Figure 24.12 indicates that females of specific species preferred males of their own kind under normal light, while under orange light they showed no preference.
- The resulting hybrids from this interaction were both viable and fertile.
- The conclusion from the study suggests that mate choice based on breeding coloration plays a crucial role in reproductive barriers and indicates recent speciation events.
Fusion of Reproductive Barriers
- Figure 24.16 exemplifies the fusion type of breakdown in reproductive barriers.
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Test your knowledge of Chapter 24 with these flashcards focused on species statistics and diversity. Discover interesting facts about plant and animal species, vertebrates, and the variations that exist among them. Perfect for biology students looking to reinforce their learning.