IB biology HL - classification and cladistics

terminal branch

endpoint of a cladogram which represents one group - AKA individual species within a clade

clade

A group of organisms and their common ancestor

nodes cladogram

the branching points on a cladogram (T). This represents the point at which the ancestral species split to form two or more clades

root

base of cladogram - This represents the common ancestor of all the clades

Why were species in the Figwort family first grouped together?

Due to their physical characteristics

What led to the reclassification of over 5000 species in the Figwort family?

Genome sequences revealing they did not share a common ancestor

what causes gradual divergence

the accumulation of mutations

what are the 3 domains

Eukaryota (plants, animals, fungi) , Bacteria (cyanobacteria, heterotrophic bacteria) , and Archaea (thermophiles and halophiles)

what made the 3 domains, eubacteria, archaebacteria, and eukaryote

Even though eubacteria and archaebacteria are both prokaryotes (lack a nucleus), scientists discovered there were actually more similarities between archaebacteria and eukaryotes than there was to the other prokaryote (eubacteria)

What is a molecular clock?

method used by researchers that uses mutation rates in DNA to estimate the length of time that species have been evolving from their common ancestor using number of differences in the base sequences

why is the molecular clock flawed

because mutation rates can vary due to other factors like mutagens whihc may cause mutation rate to accelerate

what causes mutations / can accelerate them

Mutagens (Radiation and Chemicals), and Errors as a gene is being copied

what is introgression

when fertile offspring of a cross between species then goes on to breed only with members of one of its parents species

why is it inaccurate to only look at the physical characteristics of an organism when classifying it

because physical similarities don't mean that the organisms share a common ancestor which is why scientists have developed the method to look at genome sequences and amino acid sequences

What is binomial nomenclature?

two word naming system (Genus species)

why do we classify organisms

- To identify species

- accurately determine # of known species

- Predict characteristics

- Find evolutionary links

- identify and treat new diseases quicker

taxonomic levels in order

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (did king Phil come over for great sex)

what is classfication

placing organisms in groups based on common ancestry and/or shared traits

what is the boundary paradox?

since divergence is gradual, it is hard to tell when things are different enough to be placed in separate groups

why is their difficulty classifying organisms into the traditional hierarchy of taxa

Some taxonomists might feel that two organisms are similar enough to be part of the same family while another might feel there is enough evidence to be the same genus

what is taxonomy

the science of classifying, describing and naming organisms

what is a taxa

group or level of organization into which organisms are classified

what are advantages of corresponding classification to evolutionary relationships

allows to make predictions on new species characteristics based off the characteristics of the ancestor E.G. mammal warm blooded, produces milk

what are the 2 conditions that classification must satisfy

1) every organism sharing the same common ancestor has to be in the same taxonomic group

2) in each group, all of the species evolved from the sa,e common ancestor

why do common ancestors often not exist anymore

Common ancestors often do not exist bc they have

evolved into modern species or have become extinct

which mutations occur at a predictable rate

Mutations in DNA that persist and are inherited

If the DNA base sequences or two species are similar, what does it mean?

that few mutations have occurred, and therefore the species only diverged relatively recently

what do the length of the lines separating species on cladograms often represent?

often used to represent the estimated time since they diverged

The molecular clock assumes that the mutations are not accelerated by selection pressures in the environment, population size amongst others

what are morphological traits

physical characteristics of an organism

What is wrong with a fixed ranking of taxa?

its arbitrary- doesn't show gradation of variation

What does cladistics determine?

evolutionary relationships by looking at nucleic acids and amino acid sequences

What are the rules regarding binomial nomenclature?

1. the genus name starts with a capital letter

2. species name starts with a lowercase

3. Is always in italics, but when handwritten its underlined

4. After already being used once in a text, the Genus can be abbreviated to the first letter