A3.2 CLASSIFICATION & CLADISTICS

Outline the classification of organisms and its need

1. Classification: the organisation & naming of organsims in hierarchical groups called taxa

2. Needed because of the immense diversity of species

3. Taxonomy is the classification of living things into groups based on morphological/molecular characteristics

CLASSIFICATION ALLOWS SCIENTISTS TO:

1. Determine the number of known species

2. Determine evolutionary relationships: shared common ancestors

3. Carry out conservation: identifiable species can be conserved

4. Conduct medical research: identify closely related species with medical benefits

5. Identify and treat new diseases: COVID-19 classification as a coronavirus

Outline the traditional hierarchy of taxa

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Kingdom

Phylum

Class

Order

Family

Genus Species

Outline difficulties of classifying organisms in the traditional hierarchy of taxa

1. Traditional hierarchy does not always correspond to patterns of divergence generated by evolution

2. Morphological grouping does not always correspond to divergence & shared recent common ancestor (similar traits could be due to convergent evolution)

3. Taxonomic rank: clear distinction is difficult with hybrids and if a group of organisms needs to be moved from one taxa to another

4. Species determination: the stage at which two populations are classified as species is difficult to determine/introgression could occur

Outline the clades and its advantages

CLADE: Group of organisms that have evolved from a common ancestor

1. Can be small/nested in larger clades

2. The common ancestor may be extinct

3. Organsims in the same clade will share more characteristics/phylogenetic evolutionary relationships

4. The branch length can indicate the relative number of genetic change

5. Based on molecular analysis/genetic differences in amino acid sequence/DNA base sequence

6. predictability suggests evolutionary timelines

7. Greater differences, the longer period since 2 species had common acnestor

ADVANTAGES:

1. All the members of a taxonomic group have evolved from a common ancestor

2. Characteristics are shared within a clade

3. Characteristics of organisms within the group can be predicted

Outline the use of cladogram

CLADOGRAM:

1. Tree diagrams that show the most probable sequence of divergence in clades

2. Shows the same evolutionary relationships & shared characteristics

3. Organsims in the same clade are more closely related evolutionarily

4. Nodes represent the splitting of clades from a common acnesotr

5. Branches at nodes show the time since divergence/separation and the number of differences in DNA

6. Evidence of placing organisms in the clade:

   1. Base sequence of genes/amino acids of proteins

   2. Morphological traits can be used to assign organisms to clades

Outline the molecular clock

1. Can be used to estimate the time since divergence

2. Mutation rates of DNA are steady, but only a probability

3. Cn gaive estimates

4. Because mutation rates are affected by the length of the generation time, the size of a population, the intensity of selective pressure and other facotrs

Outline the bases for construction of cladograms

Base sequences of gene & amino acid sequences of proteins is the basis for constructing cladograms:

1. Biochemical: the study of similar molecules in different species (DNA, RNA, mDNA, hemoglobin, cytochrome C)

2. Base sequence of a gene, DNA/mDNA — molecular differences can be due to mutations

3. Amino acid sequences of a protein (hemoglobin, cytochrome C)

4. Traditional methods use morphology to compare homologous structures, fossils, or comparative anamoly

Outline how cladistics can be used to investigate whether classification of groups corresponds to evolutionary relationships

1. Classifications of groups may not always reflect evolutionary relationships

2. Investigations my cladistics can be taken place.

3. Similar features may be due to convergent evolution (look at difficulties!!)

EXAMPLE: Reclassification of the figwort family

1. Traditional/Linnaena classification physical similarities were not based on evolutionary relationships

2. The flower shape & seed capsule evolved through convergent evolution

3. Different plant species adapted to similar pollinators and similar seed dispersal strategies

4. DNA evidence (three chloroplast genes) identified different common ancestors

5. Reclassification of the figwort family was required based on the molecular evidence

Outline the Classification of all organisms into three domains

1. All organsims are classified/reclasffieid into three domains using evidence from rRNA base sequences

2. The three domains are eukarya (eukaryotes), archae (prokaryotes), and eubacteria (prokaryotes)

3. They share a common ancestor but none of the three domains is an ancestor of the others

Compare & contrast the three domains

Note histone proteins, introns, ribosomes (with rRNA structure), lipids in the membranes