Lecture 6

Question 1

Cladistics

Answer 1

An approach for systematics to classify organisms using ancestral relationship as the primary criteria

Question 2

Clades

Answer 2

Group of organisms which are classified together

Question 3

Monophyletic group

Answer 3

A clade where all members are descendants of their recent common ancestor
Concept is relative to reference point

Question 4

Paraphyletic group

Answer 4

A clade where all members are descendants of their most recent common ancestor but there are more descendants of that ancestor which were not included
Is an incomplete representation of organisms with close evolutionary relatedness

Question 5

Polyphyletic group

Answer 5

A clade which includes members belonging to a different evolutionary lineage
Concept is also relative to reference point

Question 6

Algae

Answer 6

Eukaryotic photoautotrophs labelled algae
Is a polyphyletic group

Question 7

Guidelines to keep in mind during classification:

Answer 7

1. Keep track of shared ancestral and shared derived
   characters as they get passed on from the ancestor to descendants
2. Very complicated traits, shared across organisms,
   usually do not occur due to convergent evolution

Question 8

Ingroup vs outgroup

Answer 8

• Ingroup: organisms you want to classify (frog, cow, dog)
• Outgroup: a species closely related to the ingroup, but does not share any common trait (fish)

Question 9

Build a phylogenetic tree assuming these traits
arouse only

Answer 9

once during evolution

Question 10

Maximum parsimony

Answer 10

• When there are multiple ways to describe a phenomena, the simplest explanation is most likely the correct one
• Organisms are classified with maximum parsimony as the guiding principle

Question 11

Classification using genes

Answer 11

• To resolve the discrepancy, evolution events for all sites are mapped onto all possible
  scenarios
• The scenario which requires the least number of changes overall is the most parsimonious explanation

Question 12

Why are computers essential for molecular genetics

Answer 12

• Amount of calculation required to resolve the tree increase drastically with more species

Question 13

Maximum likelihood

Answer 13

resolve molecular phylogenetics while taking into account the different chances of mutations

Question 14

Why is taxonomy not straight forward

Answer 14

• Horizontal gene transfer (HGT): Genes (which represent morphological and biochemical traits) can jump from one lineage to another unrelated lineage

Question 15

What is the fundamental assumption during classification of traits

Answer 15

a trait gets transferred from ancestor to descendant via reproduction
* Horizontal gene transfer breaks this assumption and
makes it much harder to discern relationships between
organisms