Evolution I Flashcards
Missing links
Extinct organism that had the charateristics of two different groups
E.g.- Archaeopteryx
Arhcaeopteryx as a missing link
Has traits of both Class Reptilia and Class Aves
Reptilian features:
1. Teeth in jaws
2. Long tail with free caudal vertebrae
3. Weak keel-less sternum
Avian features:
1. Feathers on the body
2. Forelimbs modified into wings
3. Four toes in foot for perching
Connecting links
Living organisms that have the characteristics of two different groups
E.g. Protopterus
Protopterus as connecting link
Has characteristics of Class Pisces and Class Amphibia
Piscean features:
1. Stream-lined body
2. Paired fins
Amphibian featuresL
1. Internal nostrils
2. Presence of lungs and heart
Connecting link: Peripatus
Arthropods and annelids
Connecting link: Neopilina
Annelids and molluscans
Connecting link: Protopterus
Amphibians and fishes
Connecting link: Viruses
Living on nonliving
Connecting link: Euglena
Plants and animals
Connecting link: Platypus
Reptiles and mammals
Homologous organs
Similar in embryogenic origin and development and different in function
E.g. Humans, cats, whales and bats have the same pentadactyl limb arrangement
E.g. modification of leaves in different types of plants
Homologous organs in plants
Modification of leaves
1. Pitcher plant (insectivorous plant): leaves modified into pitchers to catch insects
2. Venus flytrap (insectivorous plant): leaves modified into jaws to catch insects
3. Poinsettia (pollination): bright red leaves resemble flower petals
4. Cactus: leaves have become spines (to decrease rate of transpiration and for defence and offence)
Analogous organs
Structurally and functionally similar, but of different origin
Analogous organs in animals
Insect, Pterodactyl, Bird, Bat wings
Analogous organs in plants
Tendril of Vine: Stem modification
Tendril of Pea: Leaf modification
Vestigial organs
Vedtigial organs are those organs that are non-functional in the possessor but were functional in their ancestors.
see examples in textbook and make flashcards later
Atavism
It is the sudden reappearance of certain ancestral but not parental structure which has either completely disappeared or reduced
* Rudimentary tail in new born babies
* Power of moving the pinna
* Large canines
* Dense hair growth
Who proposed the Recapitulation Theory?
Ernst Haeckel
What is the Recapitulation Theory?
Ontogeny recapitulates Phylogeny
Embryos in their development repeats the evolutionary history of their ancestors in the abbreviated form
E.g. gill slits/tail
Molecular evidences of evolution
- Evolution of proteins
- Evolution of nucleotide
- Universal Genetic Code
Adaptive Radiation
As organisms spread into new habitats, over millions of years, they evolve adapting to environments they inhabit. This is called Adaptive Radiation.
Who proposed the Theory of Natural Selection?
Charles Darwin
Theory of natural selection
- Enormous fertility in living beings
- Struggle for existence-
Interspecific: competition between individuals of different species- food, shelter (in the same ecosystem)
Intraspecific: competition among individuals of same species- food, shelter, mating (in the same ecosystem) - Variations under nature
- Natural selection or survival of the fittest
- Origin of species
see textbook and make flashcards
Neo-Darwinism- how is it based on Darwinism?
- This is the type of evolutionary theory we have today. It is based on the original ideas of Darwin but revised with more scientific evidence.
- Darwin’s original theory did not account for emergent species, just adaptation to environments.
Neo-Darwinists and their contributions + what is Neo-Darwinism
- Gregor Mendel came up with a mathematical formula that became the basis for evolutionary biology
- Then, Francis Crick and James Watson worked out the structure of DNA, and how genes are passed on through generation- half DNA from each parent to make new combinations.
- This natural variety, and random mutations (when something ‘goes wrong’ in the someone’s genes and leads to disabality or an advantage) make up the changes we see in species over long periods of time. The best changes survive.
- Life itself started with the first molecule of DNA, although scientists do not know how atoms manages to form living cells, and developed through mutations.
Evolution of horse
Eohippus
Height: ~0.4 m
Habitat: Lush green vegetation
Anatomy of feet: 4 digits in forelimb and 3 digits in hindlimb
Mesohippus
Height: ~0.6 m
Habitat: Dry conditions, forests and thick grasslands
Anatomy of feet: 3 digits each, conspicuous
Merychippus
Height: ~1.0 m
Habitat: Prairies, speed important to escape enemies
Anatomy of feet: Slow reduction of digits 2 and 4
Equus
Height: ~1.6 m
Habitat: Dry grasslands (exposed to predators; man tames horses for war)
Anatomy of feet: 2, 4 digits reduced to form SPLINT BONES on either side of metacarpal and metatarsal bones
Explain Darwinism based on the evolution of giraffe’s neck
- All variations in the environment
- Nature favours the superior trait
- Natural selection and survival of the fittest
Change in population
Differences between Hugo de Vries theory and Darwins theory
Hugo de Vries:
* Evolution results from mutation
* Evolution is sudden and spontaneous
* Mutation are random and directionless
Darwin
* Evolution results from variation
* Evolution is gradual
* Variation are small and directional and so is mutation
Gene pool
Gene pool refers to the total number of genes of every individual in a population, It usually involves a particular species within a population.
A large gene pool indicates high genetic diversity, increased chances of biological fitness and survival
biological fitness: ability of an organism to reproduce during its lifetime
Genetic drift
Genetic drift is the change in frequency of an existing gene variant in a population due to random sampling of organisms. The alleles in the offspring are a sample of those in the parents and chance has a role in determining whether a given individual survives and reproduces.
Genetic drift example
- In one generation, two brown beetles happened to have four offspring which survive to reproduced.
- Several green beetles were killed when someone stepped on them and had no offspring
- The next generation would have a few more brown beetles than the previous generation, but only by chance.
- These chance changes from generation to generation are known as genetic drift.
Genetic drift: two types??
- Founder effect
- Bottle neck effect
Founder effect
The founder effect can occur if a small number of individuals colonize a new area
Example:
* The gene pool for a population of flowers has genetic diversity that results in red, yellow and blue phenotypes
* A bird carries a few seeds to a new location. These seeds ‘found’ a new population
* Alleles for yellow flower colour increase in the new small population through genetic drift.
Bottleneck effect
A chance event greatly reduces the size of the population. The surviving individuals have allele frequencies different from those of the original population.
Example:
* Initial population has equal frequencies of red and yellow alleles
* Chance event reduces the size of the population and now allele frequencies are different from those of the original population.
* Which generates a new population with strong dominance of red over yellow alleles
Three types of selection in nature
- Stabilising selection: Nature does not favour the extremities
- Directional: E.g. long neck of giraffe
- Disruptive: Induced mutation, unable to adapt
explain graphically see from slides
Hardy-Weinberg principle
The original proportion of genotypes in a population remains constant if
* population size is large
* random mating is occurring
* no mutations
* no genes are introduced or lost i.e. no genetic drift
* no selection occurs i.e. all genotypes can survive and reproduce equally well.
Mathematic expression of Hardy-Weinberg principle
(p+q)^2= p^2 + 2pq + q^2 = 1
p= frequency of allele A
q= frequency of allele a
p^2= frequency of individual AA
q^2= frequency of individual aa
2pq= frequency of individual Aa
Examples of natural selection
- Industrial melanism
- Resistance of mosquitoes to DDT - Dichlorodiphenyltrichloroethane
- Resistance of microbes to antibiotics
Adaptation
Characters that are structural or functional in living organisms tens to develop over a period of time which enable them to survive and reproduce within the limits of a particular environment.
Industrial melanism- Before industrial revolution (Case 1)
- Peppered moth (grey) - Biston betularia (abundant) (UNDERLINE)
- Camouflaged due to lichen coloured trunks of oak trees
- Black mutant variety- Biston carbonaria (rare) (UNDERLINE) conspicuous and more susceptible to predation
Industrial melanism- Industrial revolution (Case 2)
- Enormous production of smoke and deposition of soot on tree trunks
- Tree trunks turned black
- Black mutant variey- Biston carbonaria camouflaged
- Grey variety moth- Biston betularia conspicruous and thus suscpetible to predation
Industrial melanism- ~Post 1950 (Case 3)
- Coal was replaced by oil and electricity as major source of energy
- Deposition of soot on tree trunks was negligible
- The tree trunks were filled with lichens
- Thus grey moth population increased and black mutant variety is rare
Example of rudimentary organs in humans
- Nictitating membrane in the eye
- Vermiform appendix at the end of the caecum
- Coccyx- tail vertebrae and tail muscles
- Non-functional muscles of the pinna
- Wisdom teeth
- Segmental muscles of the abdomen
- Nipples in male
Vestigial structures in plants
Scale leaves of Ruscus and those of underground stems
