3.2 Classification and Cladistics Flashcards
What is the need for classification of organisms?
Classification is needed because of the immense diversity of species. After classification is completed, a
broad range of further study is facilitated.
What are the possible difficulties in classifying organisms into the traditional hierarchy of taxa?
The traditional hierarchy of kingdom, phylum, class, order, family, genus and species does not always
correspond to patterns of divergence generated by evolution.
A fixed ranking of taxa (kingdom, phylum and so on) is arbitrary because it does not reflect the gradation of variation.
What are the possible advantages of classification corresponding to evolutionary relationships?
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.
Are clades considered as groups of organisms with common ancestry and shared characteristics?
The most objective evidence for placing organisms in the same clade comes from base sequences of
genes or amino acid sequences of proteins. Morphological traits can be used to assign organisms to clades.
What is the Gradual accumulation of sequence differences as the basis for estimates of when clades diverged
from a common ancestor?
This method of estimating times is known as the “molecular clock”. The molecular clock 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
Define what is meant by a cladogram
A diagram that shows the evolutionary relationships among different species or groups based on shared characteristics. It represents hypotheses about the evolutionary history of species.
Define the root of a cladogram
The base of the cladogram, representing the most ancestral lineage from which all other species in the cladogram descend.
Define the node of a cladogram
A point on the cladogram where a branch splits into two or more branches. Each node represents a hypothetical common ancestor shared by the descendants that branch off from that node.
Define the terminal branch of a cladogram
The end of a branch on a cladogram, representing the most recent species or groups. Terminal branches typically lead to the species or groups being compared in the cladogram.
What are evolutionary relationships?
The connections between species or organisms based on common ancestry. These relationships are depicted in a cladogram, where closer branches indicate more recent common ancestors.
Define what is meant by cladistics
This method classifies organisms based on shared characteristics and evolutionary relationships, typically represented in cladograms. It aims to reflect the evolutionary history and common ancestry of organisms.
Give a reclassification example and briefly explain what happened and why
reclassification of the figwort family (Scrophulariaceae). Originally, many species were grouped together in this family based on morphological traits. However, as more data (especially from molecular sources) became available, it was discovered that some similarities were due to convergent evolution—where unrelated species evolve similar traits due to similar environmental pressures, not because of common ancestry.
- This case demonstrates that classification based solely on morphology (physical traits) can be misleading, and cladistic analysis using genetic information can provide a more accurate picture of evolutionary relationships.
How do we Classify of all organisms into three domains?
using evidence from rRNA base sequences
What are the three domains that all organisms are classified into?
Bacteria, archea and Eukarya
