Classification & Cladistics

Taxonomy

the science of identifying, naming and grouping organisms

Morphology

physical features of organisms

• Difficulties:

  • highly subjective & arbitrary

  • does not show evolutionary relationships

  • e.g., dolphins & sharks could in theory be grouped together as both aquatic animal but

    • dolphins are mammals, sharks are fish

    • streamlined body shapes evolved separately rather than from a common ancestor

  • Solution: genome sequencing data → helps to avoid diffuclties w/ misleading morphology

Biological Classification

invovles puting organisms into groups or taxa

Correct classification allows scientists to:

• accurately determine # of known species

• learn about the evolution of species

• ensure that conservation is carried out when needed

• carry out medical research more quicklu

• identify & treat new diseases

Taxonomic Hierarchy

• Domain - Dear

• Kingdom - Kevin

• Phylum - Please

• Class - Come

• Order - Over

• Family - For

• Genus - Gay

• Species - Soup

Genus

indicates a group of species that are very closely related & share a common ancestor

Species

groups of organisms with shared traits

Introgression

a process by which hybrids form over many generations

• instead of an equal share of the original two species’ genetic information → unequal contribution from each species

  • demonstrates the difficulty of strict classification → resulting offspring doesn’t fit into either species neatly

Back Crossing

hybrid organism reproduces with one of the origicnal parent’s speciies to produce offspring

Advantages of classification using evolutionary relationship

• classifying according to a clade ensures close evolutionary relatives rather than arbitrary groups that look similar

  • characteristics are inherited from a common ancestory → likely to be shared

• use of DNA sequencing allowed organisms to be reclassified into

Cladistics

a natural system of classification for grouping taxa, based on characteristics that have evolved most recently

Cladogram

a diagram that represents the findings of cladistics in a visual way

• evolutionary trees that show the probable order of divergence from ancestral species & probable relationships

  • reliability depends on amount of sequence data used to construct it

Root (Cladogram)

the base form which all species branch out

Clade

(monophyletic group)

a group of organisms that have all descended from a common ancestor

• can include both living and extinct species

• classified on the basis of their shared descent from a common ancestor

Node

a place where a speciation event happened & the relative position of the common ancestor

Parsimony

provides the criteria for the construction of cladograms

• principle states that the simplest explanation is most likley

  • more likely characteristc of fur evolved once instead of twice

• cladograms are constructed using available evidence & on the basis of this principle

Sequence data

most objective method for grouping species into clades e.g,

• DNA bases

• mRNA bases

• amino acids in polypeptides

  • sequence data can provide info on the distinction of species from one another as well as how much time has passed

Sister group

a group of closest relatives

Outgroup

a group less closely related to others in the cladogram

Primitive traits (plesiomorphic traits)

characteristcs that have evolved early in history of the

• all vertebrates have spinal cords

• all insects have six legs

Derived Traits (apomorphic traits)

characteristics that have evolved more recnetly and help set apart a group of organisms from their ancestors

• e.g, within the vertebrate clade → birds have feathers vs. mammals have fur

  • closely related species share a large # of derived traits

DNA Hybridization

differences in DNA & polypeptide sequences that accumulate gradually over time → as mutations occur from one generation to the next in a species

1. sections of a single-stranded DNA are taken from two species

2. Two complementary strands are allowed to hybridize.

3. points on the DNA strand that do not bind show where the bases are different to each other

4. # of differences are recorded

Phylogeny

study of the evolutionary past of a species — very broad

Phylogenetics

a more specific term that applies to the techniques & methods used to analyze and infer evolutionary relationships

• involves the construction of phylogenetic trees

Molecular Clock

the constant rate of mutations → provides estimates rather tahn exact time periods

• rate at which mutations can be affected by e.g,

  • generation time

  • population size

  • selection pressures

Terminal branch

represents most recent species in an evolutionary lineage

Reclassification of the figwort Family

• based on observable traits (e.g, tube-shaped flower structure)

  • scientists discovered shared features were not evidence of shared ancestry → not a true clade

• actually contains several separate plant families

• paraphyletic → did not contain all descendants of a common ancestor

Archaea (prokaryotes)

single-celled organisms → often found in extreme conditions

• aka extremophiles, e.g.,

  • Thermophiles live in hot springs

  • Methanophiles metabolize methane

• circular chromosomes (70S ribosomes), histones & some introns

Thermophiles

• heat-loving

  • inhabit hot sulphur springs & hydrothermal vents & survive at temps from 70-100+ degrees C

Methanophiles

• methane-loving

  • found in the gut of ruminants, waste landfills, paddy fields & marshlands

  • produce methane as a waste product of respiration

Halophiles

• salt-loving

  • live in very salty environments (e.g, dead sea & salt mines)

Eubacteria (prokaryotes)

• bacteria has a wide range of functions

  • helps intenstines digest (probacteria)

  • apart of yogo

  • disease-ridden sometimes

Eukaryotes

• domains all other life

  • small macroscopic organisms (e.g, yeast/fungi) to trees and whales

  • cells are unique due to membrane-bound organelles

  • linear chromosome, glycerol-ether lipids, 80S ribosomes, histones & introns

5 Taxa Kingdoms

1. plants

2. animals

3. fungi

4. protoctists

5. prokarytoes