Bio lessons 8.2, 9.1, 9.2
Fossils: Evidence of Life
- Fossil Record -rich sedimentary rock shows what species lived long ago
- These fossils include soft-bodied creatures and some of the first animals with hard parts
- Some ancient animals resemble modern ones, while others are now extinct
- A time scale helps show when different organisms first appeared
What is the order Veterbrates appear in
first fish, then amphibians, then reptiles, then mammals and birds.
What are TRANSITIONAL FOSSILS
- transitional fossils helps explain how groups of organisms are connected
- Transitional fossils show steps between older and newer species
What is a Vestigial Structure?
body parts or behaviours that were once useful in ancestors but have lost most or all their original function in modern species
Ex: wisdom teeth or goosbumps
Ideas of biogeography
- Island animals : often resemble animals from the nearest continent, showing they evolved from mainland ancestors.
ex: Canary Island lizards are similar to West African lizards.
- Identical fossils found on different continents suggest the landmasses were once connected.
- Continents slowly move over time (continental drift); Africa and South America were once joined in Gondwana.
Evidence from Anatomy.
- Vertebrate forelimbs perform different functions (flying, running, swimming) but share the same basic bone structure, explained by common ancestry.
- Homologous structures : Have similar structure and origin, but may have different functions.
- Structural similarity does not always mean species are closely related if the similarity is only functional.
Analogous Structures :
Analogous structures:
- Have similar functions but different structures and origins.
- Evolved independently in unrelated species.
- Example: wings of insects vs. birds and bats
- Evolve in species from different evolutionary origins living in similar environments.
EVIDENCE FROM EMBRYOLOGY
- Embryology looks at early development before birth
- Early embryos of many animals look very similar
- Shared features, like throat pouches, point to a common ancestor
EVIDENCE FROM DNA
- DNA shows how species are related
- Similar DNA patterns suggest a shared ancestor.
- Gene studies show dogs and bears are related, and whales and dolphins are related to hoofed animals.
- Shows how mutations change DNA and pass on traits
FACTORS THAT CHANGE ALLELE FREQUENCIES
- Changing percentages, or frequencies, of alleles within populations are the small events that lead to evolution within a population, or microevolution
1.Mutations
2. Gene Flow (migration)
3. Non-random mating
4. Genetic drift
5. Natural Selection
MUTATIONS
• A mutation is a change in an individual’s DNA
• Heritable mutations can affect an entire gene pool
• More genetic variation gives a population a better chance to adapt
Gene Flow:
- Gene flow is the movement of alleles between populations.
- It happens when individuals migrate and join new groups.
Non - Random Mating
• Mating can be random or based on specific traits
• Non-random mating happens when individuals choose mates by certain looks or behaviours
• Random mating is like a draw where any pair is possible
• Non-random mating limits which traits get passed on
• Only the chosen mates add their traits to the next generation
GENETIC DRIFT
- Allele frequencies in small groups can change by chance.
- This random change is called genetic drift.
- Large groups usually stay closer to expected results.•
- Some alleles can disappear while others become the only one left.
- New alleles can return only through mutation or movement from other groups.
GENETIC DRIFT: THE FOUNDER EFFECT
- New isolated populations are formed by a few individuals
Example ;
- strong winds may carry a single, pregnant lady bug to a previously unpopulated island.
- find a new colony and produce offspring
- will carry some but not all of the alleles from the original population
NATURAL SELECTION
- If a single allele gives even a slight selective advantage, the frequency of the allele in the population will increase from one generation to the next
types of natural selection:
1. stabilizing selection
2. directional selection
3. disruptive selection.
Stabilizing selection :
- Favours an intermediate phenotype and acts against extreme variants of the phenotype.
Directional selection :
- Favours the phenotypes at one extreme over the other.
- Common during times of environmental change or when a population
migrates to a new habitat that has different environmental conditions
Disruptive selection :
- takes place when the extremes of a range of phenotypes are
- favoured over intermediate phenotypes.
Both extremes are favoured
Sexual selection :
- involves competition between males through fighting or through visual displays
- leading to traits that enhance reproductive success
What is Speciation
- Is the formation of new species from existing species. It is also called macroevolution.
- This occurs when two populations become reproductively isolated over time due to little or no gene flow between them.
- These are called reproductive isolating mechanisms
Reproductive Isolating Mechanisms
Pre-zygotic Isolating Mechanisms
Prevention of mating:
Behavioural isolation - Ex. Birds singing different songs to attract specific species
Temporal isolation - organisms reproduce at different/incompatible times, such as day/night, seasons, years, etc,
Ecological/habitat isolation - live in different locations, such as land vs water snakes
Prevention of Fertilization:
Mechanical isolation - genital anatomy doesn't match up, or flower structure is incompatible with pollen structure
Gametic isolating mechanism - egg and sperm are unable to unite and fuse
Post-zygotic Isolating Mechanisms
Revention of hybrids:
hybrid inviability - offspring of different species are weak or sterile, ex. Some plants
hybrid breakdown- hybrid embryos break down due to genetic incompatibility
hybrid sterility - hybrid offspring are produced but are infertile, ex. Mules
Types of Speciation
Sympatric speciation : speciation in which populations within the same geographical areas diverge and become reproductively isolated. More common in plants than animals.
Allopatric speciation : speciation in which a population is split into two or more isolated groups by a geographical barrier
Divergent and Convergent Evolution
Divergent evolution : common ancestor diverges to become distinct species. Ex - zebras and horses
Convergent evolution : unrelated species have evolved similar traits. Ex - birds and insects have wings but they evolved separately
Speed of Evolutionary Chang
- Gradualism : model of evolution that suggests slow and steady is the mechanism of change.
- Punctuated equilibrium : model of evolution in which long periods of stasis, interrupted with periods of divergence.
- Both models are supported by the fossil record, depending on the organisms studied