Biology Chapter 24 Flashcards

Questions and Answers

How many named plant species are on earth?

250K

How many named animal species are on earth?

How many vertebrates are there?

51K

How many species are there?

1.75 million species described to date Signup and view all the answers

Species may differ in which of the following?

DNA sequence Signup and view all the answers

What is sexual dimorphism?

Males and females appear very different. Signup and view all the answers

What are reproductive barriers?

Prevent successful breeding between organisms Signup and view all the answers

What does prezygotic mean?

Prevent zygotes from forming, impede mating, hinder fertilization Signup and view all the answers

What does postzygotic mean?

Zygote forms but does not survive or is infertile Signup and view all the answers

What are the five prezygotic reproductive barriers?

Habitat isolation, Temporal isolation, Behavioral isolation, Mechanical isolation, Gametic isolation Signup and view all the answers

What is the difference between habitat isolation and temporal isolation?

Habitat isolation is when two species live in the same general area but in different habitats, while temporal isolation is when two species breed at different times. Signup and view all the answers

What is the difference between behavioral isolation and mechanical isolation?

Behavioral isolation involves species-specific signals and behaviors to attract mates, while mechanical isolation refers to anatomical incompatibility preventing sperm transfer. Signup and view all the answers

What happens during gametic isolation in external and internal fertilization?

In external fertilization, gametes don't recognize each other; in internal fertilization, sperm cannot penetrate the egg or is killed prior to trying. Signup and view all the answers

What are the three postzygotic reproductive barriers?

Reduced hybrid viability, Reduced hybrid fertility, Hybrid breakdown Signup and view all the answers

What is the difference between reduced hybrid viability and reduced hybrid fertility?

Reduced hybrid viability occurs when the hybrid embryo dies, while reduced hybrid fertility happens when the offspring is healthy but usually sterile. Signup and view all the answers

Why is the hybrid offspring usually sterile?

Different chromosome numbers Signup and view all the answers

What happens during hybrid breakdown in the first and second generation of offspring?

1st generation is viable and fertile; 2nd generation is feeble or sterile. Signup and view all the answers

What are the issues with the biological species concept?

It's often hard to assess infertility and can't be applied to asexually reproducing species or extinct species; viable hybrids can exist for some species. Signup and view all the answers

What is an example of a viable hybrid?

Liger Signup and view all the answers

What are the two basic patterns of speciation?

Anagenesis, Cladogenesis Signup and view all the answers

What is an example of anagenesis?

Evolution of increased brain size in ancestral human species. Signup and view all the answers

What is an example of cladogenesis?

Birds' ancestors split off from other reptiles. Signup and view all the answers

What are the two basic patterns of cladogenesis?

Allopatric speciation, Sympatric speciation Signup and view all the answers

What is the difference between allopatric and sympatric speciation?

Allopatric is geographic separation restricting gene flow; sympatric involves biological factors that create two populations in the same area with reduced gene flow. Signup and view all the answers

How do populations become geographically isolated via allopatric speciation?

Extinction of connecting populations isolates two distant populations; colonization of new, geographically remote areas isolates new populations from old populations; geological processes. Signup and view all the answers

What type of biological factors cause reproductive isolation of populations living in the same area (cladogenesis via sympatric speciation)?

Genetic incompatibility, sexual selection. Signup and view all the answers

What happens during genetic incompatibility via autopolyploidy?

Failure of cell division after chromosome duplication results in tetraploid tissue. Signup and view all the answers

What is an example of a sexual selection barrier?

Female preference Signup and view all the answers

What is the result of the study from figure 24.12?

Under normal light, females preferred males of their own species; under orange light, females responded indiscriminately. Signup and view all the answers

What is the conclusion of the study in figure 24.12?

Mate choice by females based on male breeding coloration is the main reproductive barrier between the species. Signup and view all the answers

What type of breakdown of reproductive barriers is shown in figure 24.16?

Fusion Signup and view all the answers

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.