Evolution! Flashcards
Evolution defn.
- Descent with modification
- Genetic changes that occur in a population of organisms through time, leading to differences amongst them
Natural selection requirements
- must be heritable variation for a particular trait eg. beak size, colour pattern, thickness of skin.
fyi mutation arises from crossing over and independent assortment during meiosis, random fertilisation, sexual reproduction, gene and chromosomal mutations - must be differential survival and reproduction abilities associated iwth the possession of that trait
Essential features of natural selection
- Overproduction of offsprings
- Constancy of numbers
- Variation in traits between individuals within a population
- Struggle for survival and survival of the fittest
-individuals of a population are constantly competing with one another for limited resources
- individuals who are better adapted will survive till maturity and produce viable offsprings compared to others - Like produces like
- individuals who survive till maturity are likely to produce offsprings who will inherit the beneficial traits (beneficial alleles)
- this may eventually lead to speciation
Adaptive radiation
is the development of a variety of species from a single ancestral form
- it is probable that adaptive radiation led to the formation of so many speicies of galapagos finches
Smallest unit of evolution is…
aaaa population!
Types of selection
- directional selection
- one end disadvantaged (tail) - Stabilising selection/ normalising selection
- 2 extremes bad - Disruptive/diversifying selection
- intermediate bad
- polymorphism: in the same species, two or more conspicuous and distinctive forms occur in abundance
Preservation of genetic variation in natural populations
- Diploidy
- recessive alleles that are less favourable than dominant alleles can persist in a population through their propagation of heterozygous individuals - Balanced polymorphism
- is the ability of natural selection to maintain stable frequencies of two or more phenotypic forms in a population
- this allows variation to be preserved through heterozygote advantage and fequency-dependent selection
- heterozygote advantage is if individuals who are heterozygous at a particular gene locus have greater fitness than any type of homozygote, then 2 or more alleles will be maintained at that locus by NS
- freq-dep selection is that the survival and reproduction of any one morph declines if that phenotypic form becomes too common in the population - Neutral mutations
- many of the nucleotide differences in non-coding sequences appear to confer no selective advantage or disadvantage and therefore considered neutral variation. freq of these alleles may increase or decrease as a result of genetic drift
Homology defn.
similarities resulting from a common ancestor
- the more number of similarities they are, the more recently they have diverged from a common ancestor
- anatomical homology
- molecular homology
- biogeography
“the underlying skeletons of arms, forelegs, flippers, and wings of different mammals are homologous structures that represent variations on a structural theme that was present in their common ancestor”
Vestigial structures vs Atavistic structures
remnants of features that served important functions in the organism’s ancestors, but reduced role in descendents
structures that were typical of ancestors and have disappeared for generations but occasionally appear in its descendants
Anatomical homology
- comparisons of anatomical structures
- comparisons of embryological structures in embryological homology (remnants of ancestors persist in the embryos of descendants)
- fossil records (preserved remains or traces of animals, plants, and other organisms from the remote past, fossil documents descent with modification)
Molecular homology
all forms of life uses the same genetic language of DNA and RNA, and the genetic code is essentially universal. likely that all species descended from common ancestors using this code
- direct comparison of dna sequences
- comparison of mitochondrial dna sequences
- dna-dna hybridisation (estimates the ease and accuracy by which homologous strands of DNA from 2 different species can form a double helix)
- direct comparison of amino acid sequence
- measurement of immunological distance (strength of antigen-antibody reaction)
Biogeography
refers to the geographic distribution of species, influenced by continental drift
continental drift: slow movement of Earth’s continent over time
theories of biogeography further postulate that each species of flora and fauna originated only once at the Centre of Origin and from there species diversified via natural selection, as the continents drifted apart
microevolution and macro evolution
- micro. is small scale and is defined as the change in allele frequencies within a population
- macro. happens on a much larger scale that transcends the boundaries of a single species
both relies on the same mechanism of evolutionary change (mutation, genetic drift, natural selection and migration)
Various concept of species
- biological concept of species
- ecological concept of species (defined in terms of it ecological niche which is the sum of how members of the species interact with the non-living and living parts of the env)
- morphological concept of species (defined in terms of its body shape and other structural features)
- phylogenetic concept of species (defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life)
- Genetic concept of species (defined as a group of compatible interbreeding natural populations that is genetically isolated from other such groups)
Biological concept of species
Defines a species as a group of populations whose members have the potential to interbreed in nature and produce fertile and viable offsprings but do not produce fertile and viable offsprings with members of other groups
- membres of a biological species are defined in terms of reproductive capability
- gene flow occurs between the different populations of a species. ongoing exchange of alleles tend to hold the populations together genetically
- the formation of a new species hinges on reproductive isolation - the existence of biological factors/barriers that impede members of 2 species from producing viable, fertile offspring. such barriers block gene flow between the species and limit the formation of hybrids
Classification of organisms
- Hierarchical classification
- Phylogeny
Hierarchical classification
- organisation of species according to particular characteristics
- may not take into consideration evolutionary relationship between species
- refers to grouping of organisms into levels of increasingly inclusive categories
- a category in any rank unites groups in the level below it, based on shared characteristics
in the three-domain/ Linnaean system of classification, there is a hierarchy of designation:
(from the bottom) species, genus, family, order, class, phylum, kingdom, domain
Dear king phillip came over for good soup
Binomial nomenclature
combine genus and species = name
yay!
must be underlined
Homo sapiens (underline both)
Phylogeny
unlike classification that does not take into consideration evolutionary rs btw the species, phylogeny is the organisation of species according to particular characteristics which takes into consideration the evolutionary relationship between the species
- systematists use data ranging from fossils to molecules and genes to infer evolutionary relationships. Phylogenetic trees are used to depict hypotheses about evolutionary relationships
- phylogenetic tree is often constructed from a series of dichotomies (2-way branch points) where each branch point represents the divergence of 2 species from a common ancestor
What we can and cannot learn from phylogenetic trees
- intended to show patterns of descent, not phenotypic similarity
- seq of branching in a tree does not necessarily indicate the actual (absolute) ages of the particular species
- taxon on phylogenetic tree should not be assumed to be evolved from the taxon next to it
isolation mechanisms leading to speciation
- geographical isolation
- give rise to allopatric speciation
- gene flow is interrupted when a population is divided into geographically isolated subpopulations - behavioral isolation
- give rise to sympatric speciation
- courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers - physiological isolation
- give rise to sympatric speciation
- mating is attempted but morphological differences prevent its successful completion
- sympatric speciation occurs from a population that lives in the same geographic area and gene flow is interrupted by reproductive barriers
Answer template for natural selection aka cheat sheeet
- within a population, genetic variation exist due to random mutations
- identify type of isolation and hence no gene flow
- environment and force of selection
- organism A has allele coding for trait A that gives organism A a selective advantage/ disadvantage in the environment BECAUSE..
- organism A at selective advantage more likely to survive and reproduce, passing on advantageous alleles to produce fertile and viable offsprings
- over many generations, frequency of alleles that confer selective advantage would increase while frequency of alleles that confer selective disadvantage would decrease
- random mutations occur and eventually lead to accumulation of enough genetic differences, until they are unable to interbreed to form fertile and viable offsprings. allopatric/ sympatric speciation arises.
why is molecular evidence better than morphological evidence in determining phylogeny?
- molecular evidence based strictly on heritable material and can be easily described in an unambiguous manner
- morphological evidence can be confounded due to convergence, whereby similarities in morphology are due to analogous structures and not common descent
- molecular evidence are base on protein, nucleic acid sequence which are precise, accurate and easy to quantify
- Molecular evidence can detect neutral mutations
