Rise of Animals 2

Question 1

What is systematics?

Answer 1

This is the comparative study of biological diversity both past and present

Question 2

What is classification?

Answer 2

The theory and practice of ordering diversity

Question 3

What is the main goal of systematics?

Answer 3

To make biological classification reflect phylogeny or the evolutionary history of an organism, the recognition that all animal life is descended from a common ancestor provides an objective principle for ordering life with the historical pattern of evolutionary relationship of organisms allowing hierarchal classification with smaller groups of taxa nested within larger groups based on the pattern of shared ancestry

Question 4

How can cladograms depict the hierarchal pattern of taxa?

Answer 4

These use branch points or nodes which indicate the presence of a common ancestor

Question 5

What is a monophyletic group?

Answer 5

A group which includes all the ancestors from a common ancestor

Question 6

What are polyphyletic groups?

Answer 6

This is a groups which lack the most recent common ancestor of all members

Question 7

What are paraphyletic groups?

Answer 7

Groups which consist of an ancestor and not all of its descendants

Question 8

What is the requirement for something to be a characteristic?

Answer 8

They must be heritable and can be morphological, behavioural or molecular
As lineages evolve their characteristics may become modified and passed on to their descendents this evolution can be mapped on a cladogram

Question 9

What are the two basic types of characters seen in taxons?

Answer 9

Ancestral characters or plesiomorphies which are inherited from a distant ancestor and derived characters or apomorphies which arose in a more recent ancestor
Derived characters can be divided into two separate groups shared derived characters (synapomorphies) present in the common ancestor of two or more taxa and unique derived characters (autapomorphies) which are found only in one taxon these two may become interchangeable dependent on the reference point

Question 10

What is the difference in information learned from derived characteristics and primitive characteristics?

Answer 10

When derived characterstics are shared by more than one group it implies that these groups are more closely realted to each other than to groups lacking the derived characters allowing groups of organisms to be classified into monophyletic taxa and phylogeny reconstruction
Shared primitive traits however have been retained from a distant ancestor and are therefore not informative with respect to the relationships of the taxa that share them

Question 11

What is the difference between homologous similarities and analogous similarities?

Answer 11

Not all evolutionary similarity is from a common ancestor analogous structures are those which have a similar function but different origin and these cannot be used to build up phylogenetic trees homologous structures are those which are similar in structure and embryonic development even if they have very different functions

Question 12

What is the process of building a phylogenetic tree?

Answer 12

Choose the taxa whose evolutionary relationships interest you, these must be clades if you hope to come up with plausible results
Determine the characters and examine each taxon to determine the character states, all taxa must be unique
Determine if characters are derived or primitive in each taxon, this step is not absolutely necessary in some computer algorithms, this step can be helped by examining the characters present in an outgroup
Group taxa by synapomorphies not plesiomorphies
Work out conflicts that arise by some clearly sated method, usually parsimony (minimizing your number of conflicts)
Build you cladogram following these rules, all taxa go on the endpoints of the cladogram never at nodes, all nodes must have a list of synapomorphies which are common to all taxa above the node (unless the character has been modified), all synapomorphies appear on the cladogram only once unless the character was derived separately by evolutionary parallelism

Question 13

What often results in paraphyletic taxa?

Answer 13

Using plesiomorphic characters to construct a phylogenetic tree

Question 14

What often results in polyphyletic taxa?

Answer 14

Using analogous characters to construct a phylogenetic tree

Question 15

What do phylogenies based on cladistic principle often clash with?

Answer 15

Phylogenies based purely on similarity

Question 16

How can the problem of homoplasy (analogous evolution) effect molecular characters such as gene sequences?

Answer 16

There are only 4 character states in DNA there is a high probability that similarity between gene sequences can be due to convergent evolution rather than homology
Homolgous genes also mutate independently of each other so ancient divergences can result in genes that look very dissimilar
Gene duplications may also provide problems as there may be pseudogenes form which are not truly homologous

Question 17

What advantages do molecular characters have over morphological characters?

Answer 17

Molecular characters can be used to reconstruct relationships amongst very disparate organisms which lack suitable shared morphological characters for phylogenetic analysis
The rate at which some genes evolve seems to be constant over time enabling the use of a molecular clock, thus for two homologous genes the amount of genetic distance is proportional to the time that has elapsed since the lineages diverged