Ib Biology HL: A3.2 - classifications and claudistics

why is there a need of classification of species

because of the immense diversity of species. After that, a broad range of study is facilitated

levels of organisation sentense

Delicious king prawn curry or fat greasy sausages

domain

kingdom

phylum

class

order

familly

genus

species

introgression

a process by which hybrids form, but instead of having an equal share of the original 2 species genetic information, there is an unequal contribution from both species

backcrossing

a hybrid reproduces with one of the original parent’s species to produce offspring

difficulties with classifying organisms in traditional hierachies

it doesn’t always correspond to the patterns of divergence generated by evolution, because the levels of distance are fixed (doesn’t correspond to patterns of divergence generated by evolution/ doesn’t reflect the gradation of variation)

• doesn’t show evolutionary relationships

• moving organisms within the classification is difficult

• highly subjective and arbitrary

• introgression

claudistics offers a solution

claudistics

approach to biological classification in organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry.

monophyletic group

fancy word for clade

clades

A common ancestor and ALL of it’s descendants

how to assign organisms to the same clade

most objective ones are from genes/amino acid sequences, but morphological traits can still be used

ho to estimate when two members of a clade diverged from a common ancestor

• molecular clock

• differences in DNA and polypeptide sequences accumulate gradually over time, as mutations occur from generation to generation is a species

• the DNAs are compared, and differences are used to estimate when the two related species split

• can only give estimates because mutation rates are affected by the length of the generation time, the size of a population, the intensity of selective pressure and other factors. 

advantages of cladistics compared to traditional classification

The ideal classification follows evolutionary relationships, so all the members of a taxonomic group have evolved from a common ancestor. Characteristics of organisms within such a group can be predicted because they are shared within a clade.

parts of a cladogram

• root: base from which all species branch out

• node: place where a speciation even ocurred and the relative position of the common ancestor

• terminal branch: when the caldogram ends, showing species existing today

• sister group: a group of closest relatives

• outgroup: group less closely related to other in cladogram

new evolutionary classification of domains proposed recently

classification of organisms into 3 domains from 2 using evidence from DNA base sequence. Archaea got added in 1977.

• archaea

• bacteria

• eukarya

archaea

sigle celled organisms, often found in extreme conditions. can be called extremophiles

• halophiles (salt loving)

• methanophiles

• thermophiles

they have different transcription and translation, different types of ribosomes, and different types of reactions

primitive trait

characteristic that has evolved early on in the history of the organisms being studied

derived trait

characteristics that have evolved more recently and help set apart a group of ancestors

reclassification of figwort case study

all you gotta know from the syllabus, that figwort was initially classified somewhere, but then they looked at the DNA and were like “DAMN GIRL WHAT IS THAT”, and it got reclassified. that’s an example of the uses of cladistics