Two Criteria:

1. Every organism that has evolved from a common ancestor is included in the same taxonomic group

2. In each taxonomic group, all the species evolved from the same common ancestor

   
   

Advantages of classification corresponding to evolutionary relationships:

• All members of a clade will share characteristics inherited from a common ancestor (synapomorphies)

• Can be used to predict characteristics

Clades are organisms grouped based on the development of the DNA sequence and carried out based on evolutionary relationships.

• Every member of a clade shares a recent common ancestor

• Clades are monophyletic groups, meaning that they contain all of the descendants of a common ancestor

  
  

Also using rRNA, scientists discovered that "prokaryotes" consisted of two fundamentally distinct groups.

1. Cladograms are branching diagrams that represent hypotheses about evolutionary relationships.

2. They are constructed using evidence from DNA base sequences or amino acid sequences of proteins, which provide objective data about shared ancestry.

3. The more similar two sequences are, the more recently the species diverged.

4. Conversely, species with greater sequence differences likely diverged further back in evolutionary time.

• The fewer the differences between sequences, the more closely related the species are, and the more recent their common ancestor.

- Plants commonly known as figworts used to be classified in the family Scrophulariacee, and many of them have been used in herbal medicine. The name Scrophulariacee, sometimes affectionately referred to by botanists as "scrophs".

• Storing information

• Retrieving knowledge

• Identifying unknown species

2. provides the criteria for the construction of cladograms

3. choose the simplest explanation that can account for our observations. i.e. choose the tree that requires the fewest independent genetic events (appearances or disappearances of traits) to take place.

Limitations of Parsimony

• Evolution doesn’t always follow the simplest path.

• A base might mutate to a different base and then revert to the original.

• Such events can complicate the analysis and lead to misleading conclusions if parsimony is applied rigidly.

• A clade is a group of organisms that comes from one common ancestor and includes all of its descendants.

• Members of a clade usually share similar traits, inherited from that ancestor.

• Clades can be nested inside each other, like boxes within boxes.

• The study of these evolutionary relationships is called Cladistics.

For example, the organism in the picture. We can obviously see that it is eukaryotic (domain) and an animal (kingdom), but there is still a million possible species.

We can see hair and mammary glands, so we can deduce that the organism is one of the 6,500 species of mammals. Other traits show that it belongs to the order Carnivora, which narrows the possibilities to about 270 species. Further classification places it in the Mustelid family, which contains around 60 species. From there, it becomes relatively easy to identify the genus and species as Pekania pennanti, commonly known as the fisher.

• Count and record species accurately

• Understand evolutionary relationships

• Support conservation efforts

• Speed up medical research

• Identify and respond to new diseases, such as COVID-19

- Called aestivation, and botanists look for whether the flower petals overlap with each other or whether they are arranged in a spiral. Another characteristic that was used was the morphology of the nectaries, the parts of the flower that make nectar.

- Since the mid-1990s, DNA analysis of the plants within this taxon has led botanists to rethink their classification.

Analysis of zones of DNA markers, such as the nuclear

ribosomal internal transcribed spacer (ITS) region, has revealed old classification was monophyletic, meaning the taxa didn't share a recent common ancestor. Rather, the old system was grouping together plants that

belonged to separate branches, making it impossible to fit them into a cladogram attempting to show their evolutionary relationships.

WHY RE-CLASS??

lack of uniquely defining traits raises the possibility that the figwort family are not part of the same family.

Analysis of ribosomal (ITS) regions DNA sequencing of three chloroplast genes revealed taxa didn't share recent common ancestor->previous classification was paraphyletic and not monophyletic

-> In contrast, a paraphyletic group are ones that includes a common ancestor and some of its descendants but excludes other descendants

Think of a monophyletic group as a complete family tree, while a paraphyletic group is a family tree that has some branches intentionally cut off. 

so we now know that the old family Scrophulariacee was paraphyletic. Plants that were the scrophulariacee family have been given new families to belong to, such plantaginaceae, which is where we now find foxgloves. Foxgloves are no longe

considered to be figworts.

Moving the branches of the tree of life around and reclassifying a taxon in a new

branch in this manner means changing the species' circumscription.

Circumscription:

process of placing taxa where they clearly show monophyletic groups, indicating

that they all share a recent common ancestor.

1. Unclear and subjective when two populations should be grouped as separate species (A3.1). Ultimately contrived and does not always reflect evolutionary history and divergence

-> Introgression: transfer of genetic material between species following hybridization and backcrossing to the parental species. Demonstrates difficulty in species classification as the resulting offspring after several generations do not fit completely into either species, but neither does it seem to make sense to classify them as a new species

2. A fixed ranking of taxa is arbitrary – one taxonomist might argue traits in a group of species are similar enough to form a genus; another may think them different enough to form a family

3. Distinct taxa does not reflect gradation of variation and gradual divergence of species and larger groups over time. As species in a genus diverge from each other, there will eventally be sufficient diversity for the genus to split into two or more separate ones.

4. The instant in time when these separations occurred cannot be determined objectively

Hirearchy poses issues in re-classification: if an organism is moved from one taxon to another, does this mean all other members of that taxon should be moved as well?

(from Greek ‘klados' = branch)

Each clade (branched out group) consists of an ancestral organism and all of its evolutionary descendants.

Clades are organised according to evolutionary relationships - the branches show common evolutionary lineage.

Each branch point (node) represents a speciation event by which distinct species are formed via

If you want to identify the clades (a common ancestor and all its descendants):

1. Cut one branch and circle everything that follows that clade.

2. Closer branches means closer relatives. So that if any organism shares recent common ancestor, they are more closely related than those that split earlier.

2. Branch does not matter left to right, only the branching points matter.