Evolution: Formation of a New Species - Grade 12 Life Sciences Flashcards

• Evolution and Formation of a New Species

  • Topic: Evolution, Formation of a New Species (Grade 12 Life Sciences, Diversity, Change and Continuity)

  • Focus: How new species arise, variation within populations, and the processes driving speciation.

  Biological Concepts: Species, Population and Variation

  • Biological species: a group of organisms with common ancestry that closely resemble each other and have the ability to interbreed randomly to produce fertile offspring.

  • Population: a group of organisms of the same species living in the same habitat at the same time, with the ability to interbreed randomly to produce fertile offspring.

• Gene pool: the total number of alleles of all reproductive individuals in a population.

• Gene flow: the exchange of alleles between populations.

• Variation: small differences found within a population or species.

• Speciation: the formation of a new species, increasing Earth’s biodiversity.

Key Concepts and Definitions (Summary)

• Species: a group of similar organisms that can interbreed randomly to produce fertile offspring.

• Population: a group of organisms of the same species in the same habitat at the same time, capable of interbreeding to produce fertile offspring.

• Variation: small differences within a population or species.

• Continuous variation: a range of phenotypes for a trait forming a continuous spectrum; often polygenic with many alleles; influenced by the environment.

• Discontinuous variation: phenotypes fall into separate categories with few or no intermediates; often controlled by a single allele or a few genes; not influenced by the environment.

• Gene pool: total alleles in a population.

• Gene flow: exchange of alleles between populations.

• Speciation: formation of a new species.

Variation: Continuous vs Discontinuous

• Continuous variation:

  • There is a range of phenotypes for a trait, forming a continuous spectrum.

  • Traits may be polygenic with multiple alleles.

  • More alleles -> greater variety of possibilities.

  • Examples: height in humans; mass of newborns; heart rate; skin colour; size of ladybirds; milk yield in cows.

  • Environment can influence values.

  • Values can be plotted with a histogram or line graph; histogram gives a bell-shaped curve; line graph may show a smooth curve.

• Discontinuous variation:

  • Phenotypes fit into separate categories with no intermediates.

  • Usually controlled by a single pair of alleles or a small number of genes.

  • Fewer alleles -> fewer possibilities.

  • Examples: blood groups (A, B, AB, O); tongue rolling; dimples; sex; number of spots on a ladybird.

  • Environment has little to no role in influencing these traits.

  • When plotted on a bar graph, no bell-shaped curve is formed.

Graphical Representation of Variation

• Continuous variation: histogram or line graph; bell-shaped curve expected for broad samples.

• Discontinuous variation: bar graph; no smooth curve.

Mechanisms of Genetic Variation

• Genetic variation arises within species due to:

  • Genetic recombination (meiotic processes)

  • Mutations

• Genetic recombination:

  • Meiosis: crossing over of chromatids during Prophase I exchanging genetic material.

  • Random assortment of chromosomes during Metaphase I.

  • Sexual reproduction and random mating of individuals in a population.

  • Random fusion of gametes during fertilisation.

• Mutations:

  • The most important source of genetic variation.

  • Gene mutations: changes in the base sequence of DNA; types include insertion, deletion, or substitution; effects can be harmful, neutral, or beneficial.

  • Chromosome mutations: changes in chromosome number.

• Note: Mutations can lead to genotypic variation that may or may not be expressed as phenotypic variation.

Case Studies in Variation and Adaptation

• Galapagos finches (Darwin’s finches):

  • Founders arrived on the Galapagos Islands, likely from the mainland.

  • Variation in beak sizes arose; populations were separated by the ocean (geographical barrier).

  • Islands had different environmental conditions and vegetation, leading to different food resources.

  • Each group experienced natural selection independently, resulting in genotypic and phenotypic differences.

  • No gene flow between populations; when groups met again they could not interbreed, leading to new species (allopatric speciation).

  • This is a classic example of speciation driven by geographic isolation and divergent selection.

• White lions: a recessive mutant gene for white fur; not advantageous; decreased fitness because predation and hunting become easier; natural selection reduces their numbers.

Inbreeding and Outbreeding

• Inbreeding:

  • Crossing closely related individuals.

  • Occurs in threatened species with small population sizes or isolated gene pools.

  • Increases homozygosity; recessive diseases may become expressed.

  • Advantages: predictable offspring; recessive genes can be isolated; undesirable traits can be isolated.

  • Disadvantages: higher disease risk; reduced vitality; increased abnormalities; reduced heterozygosity; potential infertility; smaller gene pool.

  • Examples: Human health concerns (e.g., haemophilia, Tay-Sachs) due to recessive mutations.

• Outbreeding (outcrossing):

  • Crossing unrelated individuals, producing genetically diverse offspring.

  • Advantages: introduces new characteristics; increases genetic variation and gene pool size; can restore lost traits; increased hybrid vigor.

  • Disadvantages: loss of some characteristic traits associated with a particular breed; less predictability in offspring.

Speciation: Allopatric vs Sympatric

• Speciation: formation of a new species.

• Allopatric speciation:

  • Formation of two or more new species due to geographic/physical barrier separating the original population.

  • Key steps: geographic isolation leads to no gene flow; independent natural selection in separated populations; divergence in genotype and phenotype; when isolated populations meet again, they cannot interbreed, completing speciation.

• Sympatric speciation:

  • Formation of new species within the same geographic area without a physical barrier.

  • Mechanisms include polyploidy in plants and hybrid speciation among unrelated species.

Reproductive Isolation: Barriers to Gene Flow

• Reproductive isolating mechanisms prevent two species from producing viable, fertile offspring.

• Prezygotic isolation (before fertilisation):

  • Temporal isolation: breeding at different times of the year.

  • Behavioural (courtship) isolation: species-specific mating signals and behaviours may prevent interbreeding.

• Postzygotic isolation (after fertilisation):

  • Offspring may have abnormal development, be sterile, or have reduced viability.

Polyploidy and Hybrid Speciation (Sympatry)

• Polyploidy in plants:

  • Increase in chromosome number creates a new species in the same geographical area.

  • Involves instant speciation; crossbreeding cannot occur due to mismatched chromosome sets.

• Hybrid speciation:

  • Breeding of unrelated species can lead to a new species; this is relatively rare in nature but documented.

Case Studies in Sympatry and Speciation Mechanisms

• Cichlid fish of Lake Malawi:

  • Extremely diverse and specialized freshwater fish.

  • Speciation occurred in three stages: habitat-specific selection, food-specific selection, and sexual-specific selection.

Convergence and Divergence in Evolution

• Convergence evolution: when unrelated organisms evolve similar traits due to adapting to similar environments.

• Divergence evolution: one common ancestor gives rise to multiple, related organisms with different traits.

Founders, Bottlenecks and Isolation in Population Genetics

• Founders effect:

  • Loss of genetic variation when a new population is formed by a small number of individuals migrating to a new area.

  • The new population’s gene pool reflects only the genes of the founder members.

• Bottleneck effect:

  • A drastic reduction in population size that reduces genetic diversity.

Geological and Historical Context for Evolution

• Continental linkage: the supercontinent Pangaea is the source of today’s continents, with later divergence leading to current distribution of species.

• Allopatric speciation is often driven by geographic barriers such as mountains, rivers, oceans, earthquakes, erosion or volcanic activity that create physical separation.

Geographic Isolation and Speciation in the Galapagos Finches (Detailed Process)

• Step-by-step outline:

  1) Founders arrive on islands; a few individuals establish populations.

  2) Populations become geographically isolated by the ocean.

  3) Gene pool changes occur due to mutation, drift, and selection within each island population.

  4) Reproductive isolation evolves (behavioral, ecological, etc.).

  5) Ecological competition and different environmental conditions lead to divergent evolution.

  6) Continued evolution results in multiple distinct species with different beak sizes adapted to island-specific resources.

Practical Examination Prep: Typical Questions and Concepts

• What defines a species and how is population related to it? Answer: A species is a group of organisms that can interbreed to produce fertile offspring; a population is a group of the same species living in the same area at the same time with potential to interbreed.

• Distinguish continuous vs discontinuous variation with examples and graph forms.

• Identify sources of genetic variation and describe mechanisms of genetic recombination and mutations.

• Explain allopatric vs sympatric speciation, including barriers, gene flow, and reproductive isolation.

• Describe reproductive isolating mechanisms and give examples (temporal, behavioural).

• Explain founder effect and bottleneck effect with real-world examples.

• Describe how convergence and divergence evolution differ.

• Provide a stepwise account of Galapagos finch speciation and the role of geographic isolation and ecological factors.

• Understand the role of polyploidy and hybrid speciation in plants.

• Recognize common exam question formats (definition, concept comparisons, case-based questions) and how to structure concise, accurate answers.

Example Exam-Style Items (with concise guides to answers)

• Question: Differentiate Allopatric and Sympatric speciation.

  • Allopatric: Speciation due to geographic isolation; gene flow stops; independent evolution occurs; new species form when isolation persists.

  • Sympatric: Speciation without geographic barriers; mechanisms include polyploidy in plants or ecological/behavioural isolation.

• Question: What is the consequence of reproductive isolating barriers?

  • They prevent gene flow between populations of different species, leading to genetic divergence and eventual speciation.

• Question: Explain how a polyploid plant could become a new species in the same area.

  • Polyploidy doubles or multiplies chromosome numbers, creating immediate reproductive isolation from the parent population; crossbreeding cannot yield viable offspring with the diploid population.

• Question: Describe how Galapagos finches illustrate allopatric speciation.

  • Founding population separated by ocean; islands present different environments; independent evolution leads to reproductive isolation and new species.

• Question: What is the difference between genotype and phenotype in terms of variation?

  • Genotype: genetic makeup; variation arises from genetic differences (mutations, recombination).

  • Phenotype: observable traits; may reflect underlying genotype and environmental influences.

References to Key Terms (Glossary-Style)

• Species: group of interbreeding organisms producing fertile offspring.

• Population: same-species group in a shared habitat at the same time.

• Variation: differences among individuals within a population.

• Continuous variation: gradual trait differences across a spectrum; often polygenic and environment-influenced.

• Discontinuous variation: distinct categories with no intermediates; often gene-determined.

• Gene pool: all alleles present in a population.

• Gene flow: transfer of alleles among populations.

• Speciation: formation of a new species.

• Allopatric speciation: speciation due to geographic isolation.

• Sympatric speciation: speciation without geographic isolation (often polyploidy or behavioural/geographical divergence within the same area).

• Reproductive isolating barriers: factors preventing interbreeding between species.

• Prezygotic isolation: barriers before fertilisation (temporal, behavioural).

• Postzygotic isolation: barriers after fertilisation (hybrid inviability, sterility).

• Founder effect: genetic drift when a new population is started by a small number of individuals.

• Bottleneck effect: drastic reduction in population size leading to reduced genetic variation.

• Convergence: unrelated organisms evolving similar traits.

• Divergence: related organisms evolving different traits from a common ancestor.

• Polyploidy: increase in chromosome number; can create new species in the same area (plants).

• Hybrid speciation: new species formed from two different species.