IB Bio A3.2 classification and cladistics

What did carl linneaus do

Developed much of the systems of classification and nomenclature in use today, but not the idea of classification

What is introgression

A process by which hybrids form over many generations, but instead of having an equal share of the two original species' genetic information, there is an unequal distribution

What is backcrossing

The hybrid organism reproduces with one of the original parents to produce offspring

What is the current hierarchy of taxa

Domain, kingdom, phylum, class, order, family, genus, species

What characteristics were used to place organisms into taxa and why is that bad

Morphological, they are less reliable than molecular evidence. Phenomena such as convergent evolution and mimicry may lead to incorrect classifications.

What is the problem with classifying organisms using the traditional hierarchy of taxa (4)

• organisms that do not look alike can exhibit similar features like wings

• Does not reflect the evolution that has occurred overtime

• Recent developments in our understanding of genetics have forced us to rethink our approach 

• New species, like the red-panda have been reclassified based on genetic information that shows they are closely related with other families

Why is classification using genetic analysis better (3)

• Reflects evolutionary relationships between organisms, grouping then in clades based on ancestry

• Reflects the process of evolution and the emergence of new features

• Can be used to make predictions about the characteristics of organisms based on their evolutionary relationships

What is cladistics

A natural system of classification for grouping taxa, based on characteristics that have evolved most recently

What is a clade/ monophyletic group

A group containing the most recent common ancestor of the group and all its descendants

What is a node

A place where a speciation event takes place and the relative position of the common ancestor

What is a node

A place where a speciation event takes place and the relative position of the common ancestor

What is a root

The base from which all species branch out

What is a terminal branch

The tip of the diagram

What is a cladogram

A diagram that represents the findings of cladistics (ancestor-descendent relationships) in a visual way, to compare the traits of various organisms and explore evolutionary links

What is a sister group and an outgroup

• A sister group is a group of the closest relatives

• An outgroup is a group less related to others in the cladogram

What is cladistic analysis based on

The idea that shared genetics or traits that have been passed down from a common ancestor are used to identify a clade. So, they compare the base sequence of amino acids, or traits of an organism to see which were most likely to have originated from a common ancestor

What is the estimate of when clades diverged from a common ancestor based on 

Molecular clock, which depends on Gradual accumulation of sequence differences, which are the result of mutations and accumulate over long periods of time, assuming the mutations happened at a constant rate, the number of differences can estimate the time

What is the molecular clock's estimates based on

• Size of a population

• Selection pressures

• Genome size

• Degree of randomness

How can the differences in DNA be found

Through DNA hybridization, where the differences in DNA are counted

What are derived traits/ apomorphic traits

Characteristics that have evolved more recently and help set apart a group of organisms from their ancestors

What are primitive traits/ plesiomorphic traits

Characteristics that have evolved early in history of the organism being studied

What as an example of a plant that was reclassified and why

• The figwort family was once very large, characterized by shared morphological traits

• When scientists carried out genetic  analysis on a gene, they discovered that they need to be reclassified, so now they got seperated

Original classification systems recognized two major domains: eukaryotes and prokaryotes. What changed?

• When the base sequences of ribosomal RNA were determined, it became apparent that they were two distinct groups of prokaryotes

• They are now three, eubacteria, archea, and eukaryota, where archea and eukarya are sister groups

What are the different types of archea (4)

• Halophiles: salt loving

• Thermophiles: heat-loving

• Methanophiles: methane loving

• Extremophiles: prefer extreme conditions

What is the eukarya domain

Includes all other life than bacteria and archea, have membrane bound organelles