A3.2

Question 1

Difficulties in Classification

Introgression?

Answer 1

• A form of hybridization form whereby hybrids form over many generations but with an unequal contribution of each species.
• Occurs when early hybrids backcross with one of the original parent species.
• These hybrids are difficult to classify into set taxa.

Question 1

Difficulties in Classification

Molecular Systematics?

Answer 1

• The process of classifying organisms using molecular differences in their protien sequences of DNA base sequences

Question 2

Difficulties in Classification

Phylogenetic Trees?

Answer 2

• A diagram that shows the evolutionary relationships of a group of species that developed from a single ancestor
• It’s contructed using genetic evidence from genes/proteins
• Can be used to identify clades or monophyletic groups.

Question 3

Difficulties in Classification

Clade?

Answer 3

• A group that comprises the most recent common ancestor of that group and all of its descendants.
• They can be big or small - but include their common ancestor, and ALL that come from that ancestor are included.

Question 4

Difficulties in Classification

Derived traits?

Answer 4

• Observable raits that have evolved more recently when looking at clades.
• They separate lineages.
• These traits are shared by closer related traits only
• They’ve often evolved from modifications to primative traits (shared by all in a clade) and may have led to speciation.

Question 5

Difficulties in Classification

The necessity of classification

Answer 5

• Important because there exists such a diverse range or organisms, hence, trying to identity on many species requires some system of organization.
• By organizing, it allows for a scientific naming system, meaning organisms can be identifieid

Question 6

Difficulties in Classification

Limitations of using fixed rankings of taxa

Answer 6

• May not reflect gradual divergence of species and some grouping have high levels of similarity while others have less.
• Hybridisation also makes it hard to place organisms.

Question 7

Difficulties in Classification

The challenge of introgression hybrids.

Answer 7

• Fixed hierarchy taxa intends to fit organisms into discrete categories.
• Introgression hybrids often bear much similarity to one species yet also contain some DNA of the other meaning they don’t fit nearly into 1 category, nor do they truly belong as their own species (due to their ability to corss-breed with another species).

Question 8

Difficulties in Classification

Benefits of Evolutionary Relationships for Classification

Based on objective DNA evidence

Answer 8

• Categories are not subjective/arbitrary but based on quantitative data.
• By determining a shared common ancestry, grouping becomes meaningful and not based on different opinions.
• Also used for determining clades.

Question 9

Difficulties in Classification

Monophyletic Clades

Answer 9

• A monophyletic group means they all share a common ancestor and include all who share that common ancestor.
• Can be small or large.

Question 10

Difficulties in Classification

Determining Clades

Answer 10

• Based on morphology - organisms that shared a derived trait.
• More accurately, looking at gene sequencing and finding a group who can be linked to a shared common ancestor

Question 11

Cladograms and Evolutionary Clocks

DNA Hybridization?

Answer 11

• A tool used to measure genetic similarity between 2 species.
• A single strand of DNA is taken from one species and then that same gene is taken from another species and the complemenary strand(the other strand from the first species) is added.
• Where two species have the same sequence, the bases shuold form H-bonds due to their complementary nature.
• Where there is a genetic difference between species, the bases will not bond.
• This is used to quantify the differences between the species.

Question 12

Cladograms and Evolutionary Clocks

Molecular Clock?

Answer 12

• A tool to estimate the time that species diverged from one another based on the number of base sequence differences between various species.
• By comparing how many base differences there are, a rate of mutation can be determined.
• Once this rate is determined, the number of differences between species is used to provide a time to estimate for their speciation event.

Question 13

Cladograms and Evolutionary Clocks

Cladogram?

Answer 13

• A visual representaiton of the evolutionary history of a clade that shares a common ancestor.
• Should be constructued based on DNA differences but often also tries to show the derived characters that separate the species.

Question 14

Cladograms and Evolutionary Clocks

Sister group?

Answer 14

• The most closely related two species that share the most recent common ancestor together on a cladogram.

Question 15

Cladograms and Evolutionary Clocks

Outgroup?

Answer 15

• The least related species(to the others) on a cladogram.
• They share the same distanct common ancestor but were separated at the first speciation event so have the least similarity to the other species (both morphologically and in terms of their DNA).

Question 16

Cladograms and Evolutionary Clocks

Using Genetic Differences to estimate Divergence timing

Answer 16

• This method is an objective and quantitative tool.
• It’s helpful vecause it often takes a number of allelic changes before protiens, and therefore its traits diverge.

Question 17

Cladograms and Evolutionary Clocks

Limitations of Molecular Clocks

Answer 17

• They make the assumption that mutation rates are constant.
• They can also be influenced by:
  1.) Time between generations.
  2.) Population size.
  3.) Intensity of selective pressure.

Question 18

Cladograms and Evolutionary Clocks

Types of Data used to construct Cladograms

Answer 18

• While often constructed based on dervied traits, they are most accurate when they use molecular evidence
• Historically, amino acid sequences were compared.
• With the next-gen sequencing, DNA sequences are used more now, which is helpful for distinguishing between closely related species.

Question 19

Cladograms and Evolutionary Clocks

Parts of a Cladogram: Node

Answer 19

• The node shows a split where one branch goes in one direction and the other in another direction.
• The node shows speciation and where they last shared a common ancestor.
• Should in theory also reveal who their common ancestor is

Question 20

Cladograms and Evolutionary Clocks

Parts of a Cladogram: Root

Answer 20

• The base of the cladogram that shows the common ancestor to all of the clades in the cladogram.

Question 21

Cladograms and Evolutionary Clocks

Terminal Branches

Answer 21

• The end of the cladogram or the species at the end of the branch
• It reprents the most recently evolved of the organisms in the clade.
• Is often also the most complex organisms of the clade or the organism with the most derived traits.

Question 22

Cladograms and Evolutionary Clocks

Applying parismony to Cladograms

Answer 22

• Parismony in science is the idea that when given several possible explanations, it is best to choose the simplest one.
• Looking at cladograms, we look for ones that involve fewer speciation events and that don’t try and label more derived characters than necessary to illustrate differences between species.