A3.2 classification and cladistics (year 6)

Question 1

Advantages of phylogeny instead of morphology

Answer 1

Morphology - the classic classifying system based on kingdom, phylum etc is flawed as it assumes that the system is ranked and each rank must be respected, although there are many hybrids which do not obey these classifications

Phylogeny - the study of an evolutionary past of a species, using a PHYLOGENTIC tree.
adv- it is not based on arbitrary, subjective or contrived categories, instead reflecting the species natural gene sequences.

Question 2

What is a clade

Answer 2

clades can also be called a monophyletic group, meaning that it is a group comprising of the most recent common ancestor of that group and all its descendants, and can comprise of just one or many species.

the characteristics of organisms in a clade can be predicted

Question 3

Describe how cladistics work

Answer 3

Cladistics is grouping based on the characteristics that have evolved most recently. To decide how close a common ancestor is, researchers can look at DNA and animo acid sequences, or they can look at which traits are shared between species- these traits are divided into primitive and derived traits.

primitive (plesiomorhpic traits) - characteristics that have a similar structure and function and evolved early in the history of the organisms being studied
derived (apomorphic traits) - also characteristics that have similar structure and function but have evolve more recently, in the form of modifications of a previous trait.

e.g. in a clade all organisms would have primitive traits, but the clade would be broken down into subgroups as not all organisms have derived traits

Question 4

Describe the molecular clock

Answer 4

an estimation used to estimate how far back in time 2 related species plit from a common ancestor.
This is as differences in polypeptides accumlate gradually over time. However the evolutionary clock can only estimate as mutation rates area affecgted by factors such as length of generation time, size of population, intensity of selective pressure etc.

a technique used is DNA HYBRIDIZATION, where two different strands from different species are placed next to one another: where the base pairs connect, there is a match, where they repel, there is a difference in DNA sequence.

Question 5

Describe the features of a cladogram

Answer 5

node (circle at an intersection) - place where a speciation event happened, representing a common ancestor

root - base of the cladogram showing the common ancestor to all the clades in the cladogram

terminal branch - the end of a branch representing the most recently evolved of the organisms in the clade.

Question 6

Describe the 3 domains (classification hierachy)

Answer 6

Archaea - single celled organisms distinct from bacteria

Eubacteria - bacteria e.g. bacteria in yogurt, intestines.

Eukarya - ALL other life other than Archaea and Eubacteria, from single-celled yeast to eukaryotes.

Question 7

Difference btwn archaea and bacteria

Answer 7

• archaea have different subunits for their ribosomes, 16S rRNA
• there are metabolic reactions carried out by archaea that no bacteria can perform e.g. synthesizing methane
• the ways in which archaea carry out transcription and translation share more characteristics with eukaryotic transciptions and translation than with bacteria
• some physical features of archaea are different from. bacteria, such as the types of molecule sused to build their cell membrane and cell wall.