Determined Relatedness

Question 1

Evidence of relatedness

Answer 1

> Structural morphology: Homologous structures, vestigial structures
Molecular homology: DNA sequences (mtDNA), Amino acid sequences

Question 2

Structural Morphology

Answer 2

> Plays an important role in determining the relationships between species.
The analysis of structural similarities and differences is useful for comparing modern species as well as making connections between today’s biodiversity and extinct ancestral species.

Question 3

Homologous Structure

Answer 3

> A structure within a group of species that performs a different function yet has the same underlying structure.
Can be seen in a range of organisms that share a recent common ancestor.
The more similar the homologous structure between species, the more closely related these species are, and the more recently they shared a common ancestor.
The different selection pressures within each environment have resulted in the original appendage of the ancestral species evolving into various forms seen in its descendant groups today.

Question 4

Vestigial Structures

Answer 4

> An organism with a structure that is no longer functional but served a purpose in a common ancestor.

Question 5

Divergent Evolution

Answer 5

> Is the evolution of two different species from a common ancestral species due to exposure to different selection pressures and accumulation of mutations.
Isolated species and populations accumulate genetic differences and their homologous features may become different, with different functions.
Homologous and vestigial structures can both be evidence of divergent evolution.

Question 6

What’s the difference between divergent evolution and speciation?

Answer 6

> These processes are not mutually exclusive.
Speciation is the process by which populations genetically diverge until they become different species.
Divergent evolution describes a speciation event where a common ancestor speciates into two more more descendant species.

Question 7

Convergent Evolution

Answer 7

> When two not closely related species evolve structures (via natural selection) with similar functions when exposed to similar selection pressures.
If the most recent common ancestor between the species did not have that similar trait, then the two lineages must have evolved this trait independently.

Question 8

Molecular Homology

Answer 8

> Advances in technology have given scientists the capacity to compare species at a molecular level.
Particularly useful when species of interest have no structural similarities.

Question 9

Molecular Clock

Answer 9

> The use of molecular homology in determining species relatedness can be described as a molecular clock.
States that measuring the number of differences in DNA or amino acid sequences between organisms indicates how closely related they are.

Question 10

What two fundamental ideas is the Molecular Clock based on

Answer 10

> Greater molecular similarity indicates a more recent common ancestor
Less molecular similarity indicates a less recent common ancestor

Question 11

Amino Acid Sequences

Answer 11

> Determining relatedness between species can be done by analysing amino acid sequences in proteins that are common between the species of interest.
As two species diverge from a common ancestor, they accumulate different mutations in their DNA and start accumulating differences in the amino acid sequences of their proteins.
The more time that has passed since the two species diverged from the common ancestor, the more differences there are between their amino acid sequences.
Amino acid sequences will not reveal all differences in the DNA sequence between species.

Question 12

Amino Acid Sequences

Answer 12

> Point mutations may not cause a difference in the amino acid sequence because the genetic code is degenerate.
Consequently, differences in amino acids accumulate more slowly than differences in DNA.

Question 13

DNA Sequences

Answer 13

> The order of the nucleotides in the DNA indicates the evolutionary relationship between species more accurately than the amino acid sequence.
When conducting DNA analysis to determine relatedness, the sequence of bases between the two (or more) species is compared, to identify similarities and differences.
The greater the degree of similarity, the more recently the species shared a common ancestor.
Species that diverged long ago would have had more time for mutations to accumulate, therefore have more differences in DNA sequences.

Question 14

DNA Regions

Answer 14

> In Eukaryotic cells, DNA can be found in several organelles.
The DNA region most appropriate for analysis depends on what organisms are being studied and how far back in time they have diverged.

Question 15

Mitochondrial DNA

Answer 15

> Like chloroplasts, mitochondria contain their own genome (mitochondrial DNA or mtDNA) because they once existed as free-living organisms before being engulfed by our eukaryotic ancestors.
Is double stranded and circular.
Replicates by binary fission.
Is inherited through the maternal line of sexually reproducing organisms (i.e. from mothers to their offspring)
> A father’s mtDNA is not passed on to his offspring.

Question 16

Nuclear DNA

Answer 16

> Nuclear DNA is inherited as a combination of both maternal and paternal DNA.
The recombinant nature of this DNA results in changes to DNA sequences at every generation, making backtracking through a species’ ancestry a complicated process.

Question 17

Mitochondrial DNA: three main advantages of using mtDNA over nuclear DNA as a molecular clock:

Answer 17

> High mutation rate:
> Higher than the coding region of nuclear DNA
> Making it more useful for more closely related species, but also between diff pops of the same species
No recombination
> Meaning offspring are a unique mixture of their parents’ nuclear DNA
> mtDNA is inherited from a single lineage, the maternal line
> Making it possible to trace unbroken lineages

Question 18

Human Origins

Answer 18

> Studies have found, of all racial groups, African people have the greatest diversity in their mtDNA, as measured by the number of mutations.
This infers that African mtDNA is the oldest, and therefore the origin of humans lies in Africa.

Question 19

Mitochondrial Eve

Answer 19

> Researchers have been able to trace maternal lineages using mtDNA and shown that all modern humans share a common female ancestor that lived in Africa about 200,000 years ago.

Question 20

Linnaean Classification System

Answer 20

> In the Linnaean system of classification, organisms are organised into a hierarchy of groups reflecting their evolutionary relationships.
Organisms were originally grouped based on their physical similarities.
> It was hypothesised that organisms with features in common had the same evolutionary origin.
Comparison of amino acid and DNA sequences has allowed the discovery of previously unknown evolutionary relationships and the re-classification of organisms into more accurate taxonomic groups.

Question 21

Phylogenetics

Answer 21

> Is the study of the evolutionary history of an organism or group of organisms.
The goal of phylogenetics is to describe an organisms relationships, such as from which organisms it may have evolved or to which species it is most closely related.
Represent an evolutionary hypothesis.

Question 22

Phylogenetics are useful for displaying

Answer 22

Are useful for displaying:
> Relatedness between taxa (taxonomic grouping)
> The timeline of lineages (a direct sequence of evolution from a common ancestor)
> Shared characteristics of different taxa

Question 23

Reading Phylogenetic Trees

Answer 23

> Root: The line at the base of the phylogenetic tree. Represents the common ancestor for all members of the phylogenetic tree
Branch: Each represent the process of speciation (evolution) that has resulted in the formation of the final species from the common ancestor.
Branch lengths are proportional to the number of nucleotide changes that have occurred during divergence from the common ancestor.
The total length of all the branches connecting two taxa is equal to the evolutionary divergence between them.
Nodes: Also known as branching points.
Represent the most recent common ancestor of the descendant species that have developed as a result of divergent evolution. Represent a speciation event.
Leaf: Is the end of a branch.Where the species of interest are written.

> Determining how recently species shared a common ancestor can then be used to infer the relatedness between them.
If two populations become isolated from each other, they will accumulate different mutations in their DNA.
The more mutations that accumulate between two species, the more time will have passed since the two species shared a common ancestor.

Question 24

Constructing Phylogenetic Trees

Answer 24

> The order of the taxa is different in the below examples, however the configuration of the branches connecting them remains the same.
When constructing a phylogenetic tree, provide a timeline that indicates the most ancestral to most recent species.
Essential because is gives the reader direction.