Chapter 9: Relatedness

Question 1

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Define relatedness

Answer 1

• Relatedness refers to how recently species split from a common ancestor

Question 2

Define structural morphology

Answer 2

• Structural morphology is the process of comparing similarities in body structures to infer relatedness
• Often done using the fossil record

Question 3

Define molecular homology

Answer 3

• Molecular homology is the process of comparing similarities in molecular structures to infer relatedness
• Focuses on DNA and amino acid sequences

Question 4

Define developmental biology

Answer 4

• Developmental biology is the process of comparing embryos of different species to infer relatedness

Question 5

Describe and provide an example of homologous structures

Answer 5

• Homologous structures are structures that have evolved from a common ancestor to have differences in form and function but similarities in structure
  
  • They arise through mutations and selection pressures
• E.g. Mammalian forelimbs
  
  • Each mammalian limb has a similar number of bones arranged in the same basic pattern
  • However, each limb may serve a different function

Question 6

Explain how homologous structures arise

Answer 6

• Mutations that change when and where genes are active
• Different selection pressures selecting for a favourable phenotype

Question 7

Describe and provide an example of analagous structures

Answer 7

• Analagous structures are structures in different species that share similar functions but are different in structure
  
  • They emerge when organisms are under similar selective pressures (convergent evolution)
  • They do not derive from a common ancestor
  • They provide evidence for natural selection
• E.g. The wings of birds and insects
  
  • These organisms do not have a common ancestor with wings but have evolved the ability to fly to aid their survival (selective pressures)
  • While the wings of birds and insects provide the same function, they have different structures

Question 8

Describe and provide an example of vestigial structures

Answer 8

• Vestigial structures are structures that are non-functional remnants of structures that were functional in ancestral species
  
  • They suggest the evolutionary origin of species
• E.g. Goosebumps
  
  • For our ancestors, goosebumps insulated the body by trapping warm air against the skin
  • Goosebumps no longer perform this function in modern humans

Question 9

Explain why organisms have vestigial structures

Answer 9

• Organisms retain genes coding for a particular feature due to its presence in an ancestral species
• This feature is then developed (it is not lost through natural selection as it is not disadvantageous)
• However, due to different selection pressures, it no longer serves its purpose

Question 10

Define orthologous proteins

Answer 10

• Genes or proteins derived from a shared ancestor in which the primary function is conserved

Question 11

State 2 limitations of amino acid sequencing

Answer 11

• Multiple codons can code for the same amino acid (redundancy)
• Some mutations, such as silent mutations, are not visible and are therefore not identified during amino acid sequencing

Question 12

Explain comparative genomics

Answer 12

• Comparative genomics involves the comparison of DNA between different organisms to identify their evolutionary history
• The more recent the divergence of two related species from a common ancestor is, the greater the similarity in their DNA and their arrangement within the genome

Question 13

Explain why molecular homology can measure relatedness

Answer 13

• Mutations can occur in DNA over time
• Fewer differences in DNA and amino acid sequences between species suggest a closer degree of relatedness between them

Question 14

Explain whether the use of structural morphology or molecular homology will allow a more accurate understanding of relatedness

Answer 14

• Molecular homology can show that two species are closely related despite differences in their structural morphology
• Different species may have similar features that evolved independently (through analogous evolution), hence, using structural morphology may incorrectly suggest relatedness
• Thus, molecular homology is more accurate when inferring relatedness

Question 15

Explain phlyogenetic trees

Answer 15

• A diagram showing inferred evolutionary relationships between species based on their physical and genetic similarities and differences
• Tips represent species
• Nodes represent a common ancestor
• Branches indicate a speciation event
• The length of a branch indicates the amount of time that has passed since divergence
• Sister taxa are two groups (species) with a common ancestor that is not shared with other groups