A3.2- Classifications and Cladistics

The need for classification of organisms

Because of the immense diversity of species

Species

Basic level of classification

Taxon

Any classificatory group (plural: taxda)

Difficulty of classifying orgnaisms into traditional hierarchy of taxa

Traditional hierarchy of kingdom, phylum, class, order family, genus and species do not always correspond to patterns of divergence by evolution

Divergence

Evolutionary process where population diverges /splits) into 2+ descendant species and are gradually becoming dissimilar

Advantages of classification corresponding to evolutionary relationships

• Ideal classification follows evolutionary relationships

• All members in taxonomic group evolved from a common ancestor

• Characteristics of organisms can be predicted because of shared clade

Examples of species of bat

• Bats are classified as mammals, some predictions can be made then:

  • New species of bat will have:

    • a four-chambered heart

    • hair

    • mammary glands

    • placenta

    • navel/belly button

Examples of species of daffodils

• Some types of daffodil produce galanthamine

  • Used for treatment of Alzheimer's disease, there is strong evidence that all species in the genus Narcissus evolved from a common ancestor

  • Reasonable to predict that alkaloids are synthesised by Narcissus species

Evidence for placing organisms in the same clade

Base sequences of genes or amino acid sequences of proteins

State what is used instead when sequence data is not available to provide/present as evidence

Morphological traits

Clade example drawing

(draw and label)

• Smaller clases are nested within larger ones

Molecular Clock

Method of estimating times since two species diverged from a common ancestor

Reason why molecular clocks can only give estimates

Mutation rates are affected by:

• Length of generation time

• Population size

• Intensity of selective pressure

• Etc

How are cladograms constructed

Sequence Analysis

Cladogram + sample drawing for humans and primates

A branching diagram that represents ancestor-descendant relationships

(draw and label)

Analysing cladograms

• Cladogram is a tree diagram with a number of branches

• Root → Base of a cladogram

• Node → Branching points that represent hypothetical common ancestor

• Terminal Branch → Ends that represent individual clades

The new 3 major categories of organsisms

• Eubacteria

• Archae

• Eukaryota

Why is classification not regarded as appropriate anymore

Because prokaryotes are so diverse