evolution iv - phylogeny and its reconstruction Flashcards
define biodiversity
biodiversity is the variety of living organisms and their range of behavioural, ecological, physiological & other adaptations in an area such as an ecosystem
define systematics
systematics is the discipline of biology involving the scientific study of the diversity of organisms, focusing on classifying organisms & determining their evolutionary relationships. systematics connects classification with evolutionary history.
systematists classify organisms based on current data from morphology, developmental biology, fossil records, behavioural biology & molecular biology
define taxonomy
taxonomy is a component of systematics, and is the science of naming, describing & classifiying the diversity of organisms
define phylogeny
phylogeny is the organisation of species according to particular charactersitics which takes into the consideration the evolutionary relationship between species.
phylogeny reflects evolutionary history and represents a hypothesis about patterns of evolutionary relationships among species. it showcases the branching relationships of organisms as they give rise to multiple descendant species over evolutionary time
what is a phylogenetic tree?
a phylogenetic tree is an evolutionary tree that shows a visual representation of a phylogeny to illustrate lineages and their evoluionary relationships
why are characters/traits critical in the study of phylogeny?
- we use observations of traits to infer the patterns of ancestry & descent among populations. we then can represent these patterns in graphical form as a phylogenetic tree
- by mapping out additional traits onto a phylogeny, we can study the sequence & timing of evolutionary events
character - any observable characteristics of organisms (coat colour)
traits - specific values of a character (brown coat, white coat)
what are clades?
clades are monophyletic groups, which are taxonomic groups consisting of all descendants of the group’s most common ancestor and no other members.
a clade hence always consists of a group of species that share a single recent common ancestor.
‘morphological data can be used to reconstruct phylogeny.’ true or false
true.
phylogeny can be inferred from morphological & molecular homologies among living organisms. (homologous structures/divergent evolution & analogous structures/convergent evolution)
what are shared ancestral characters (plesiomorphies)?
shared ancestral characters are features that were present in an ancestral species and remain present in all groups descended from that more distant ancestor.
homologous feature
what are shared derived characters (synapomorphies)?
shared derived characters are novel traits that evolve when 2 populations become separated and begin to evolve independently.
also homologous feature!
difference between shared derived & shared ancestral: shared ancestral traits are shared by ALL members of a group with the same common ancestor, but shared derived traits are more unique to a particular subgroup within the same group that shares a common ancestor.
the shared ancestral traits evolved first, while the shared derived trait is a more recently evolved one.
why can evolutionary relationships be inferred by analyzing synapomorphies?
- synapomorphies identify evolutionary branch points
- synapomorphies are nested - each branhinge vent adds one or more shared derived traits, so the hierarchy described by synapomorphies also describes the hierarchy of branching events
why are molecular homologies used in reconstruction of phylogeny?
- when a new species evolves, it does not always exhibit obvious phenotypic differences when compared to closely related species. some of their DNA, proteins & other molecules are different.
- macromolecules that are functionally similar in 2 different types of organisms are considered homologous if their primary sequence is similar. this helps us understand phylogenetic relationships that cannot be determined by non-molecular methods like comparative anatomy.
- genetic sequences in DNA/RNA/a.a. sequences changeo ver the course of many generations due the accumulation of mutations.
‘the greater the degree of homology/similarity in the primary sequences of maacromolecules between 2 species, the more closely related the 2 species are considered to be.’ true or false.
true >v<
the number of differences in certain DNA/RNA/a.a. sequences may also reflect how much time has passed since the groups diverged from a common ancestor
(briefly) what is multiple sequence alignment?
- comparable sequences (sequences that share some degree of similarity) from the species being studied are aligned
- if the species are closely related, the sequences probably differ at only one or a few sites. contrastingly, comparable nucleic acid sequences in distantly related species usually have different bases at many sites and may have different lengths, as insertions & deletions may accumulate over long periods of time
how can amino acid sequences be compared to infer phylogeny?
- homologous proteins are proteins that are evolutionarily related, e.g. cytochrome c
- homologous proteins from different species may have polypeptide chains that are (nearly) identical in length. many positions in the aa. sequences are occupised by the same residue in all species, and are invariant sequences of conserved sequences. other positions show considerable variation in the a.a. residue from one species to another, and are called variable residues
- cytochrome c is found in the mitochondria of every aerobic eukaryote, so it is used to compare amino acid sequences. (we assume that each molecule of cytochome c in different organisms has descended from a precursor cytochrome, i.e. these molecules are homologous)
advantages of molecular methods in the study of evolutionary relationships?
- molecular data is genetic. anatomical, behavioural and physiological traits often have a genetic basis, but the relationship between the underlying genes and the trait may be complex. nucleic acid/a.a. sequence variation has a clear genetic basis that is easy to interpret
- molecular methods can be used with all organisms as all living organisms possess nucleic acids and proteins, so molecular data can be collected from any organism
- molecular methods can be applied to a huge amount of genetic variation. an enormous amount of data can be accessed by molecular methods.
- the molecular approach helps us understand phylogenetic relationships that cannot be determined by non-molecular traits. all organisms have certain molecular traits in common, like ribosomal RNA sequences, that offer a valid basis for comparison among all organisms
- molecular data is quantifiable. nucleic acid & a.a. sequence data is precise, accurate & easy to quantify, facilitating the objective assessment of evolutionary relationships
- molecular data often provides information about the process of evolution.
- the database of molecular information is large and growing, which can be used for making comprehensive evolutionary comparisons between many groups of organisms
- molecular methods allow us to reconstruct phylogenies among groups of present-day prokaryotes and other microorganisms for which we have no fossil record at all.
