DNA Sequence Comparisons Between Species

EXPLORING MOLECULAR EVOLUTION

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Results of your pairwise alignment comparing the beta globin gene in humans and in chimps:

1. Data about the alignment can be found below the blue/black alignment chart. How many base pairs (bp) are there in the beta globin gene for:
1. The chimp?

• 600

2. The human?

• 626

2. A blue asterisk indicates that the nucleotides (bp) in both sequences are the same, we say they are conserved. What percentage of the beta globin sequence is conserved in chimps and humans? (Don’t include the insertion at the beginning of the human gene). This percentage is often reported as a similarity “score” below the alignment.

• 99

3. Would you expect the protein structure to be highly similar or markedly different in the chimp and the human? Explain.

I would expect the protein structure to be highly similar because there is so much DNA that is similar.


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Results of your pairwise alignment comparing the beta globin gene in humans and in chickens:

1. What is the percentage of sequence conservation between the beta globin gene in chickens and humans?

Chickens: 601
Humans: 626

2. Looking at the two pairwise alignments you have performed, would you expect the beta globin protein found in humans to be more similar to that found in chickens or that found in chimps? Explain.

I would expect the beta globin protein found in humans to be similar to that found in chimps because their DNA is more similar to humans than the DNA found in chickens.

3. Do the results achieved by running these alignments support the results on evolutionary relationships determined by scientists using anatomical homology (similarities)? Explain.  

The results achieved by running these alignments does support the results on evolutionary relationships determined by scientists using anatomical homology because they are similar in ancestry.

Results of your multiple sequence alignment comparing the beta globin gene in a variety of animal species:

1. Examine the Unrooted Tree produced.  

Record the species at the end of each branch on the unrooted tree shown below.



                                   

2. Based on the information in the unrooted tree:

1. Which two species appear to be most closely related to each other? Explain your choice.

The human and the chimp are the two species that appear to be the close.

2. Which two species seem to be the least closely related to each other? Explain your choice.

The chicken and the mouse seem the be the least close because they are the farthest from each other on the tree.

3. Comparative evolutionary distance between species is indicated by the length of the clades they are on. Give the comparative evolutionary distance (by percentage similarity “score”) between:

1. The mouse and human

• 75

2. The wallaby and the human

• 79

3. The chimp and the human

• 99

Comment on the significance of these results given your knowledge of mammalian groups.

Results of your Rooted Phylogenetic Tree:

1. Examine your Rooted Phylogenetic Tree and record the species at the end of each branch.  

2. Based on this tree diagram, which species is/are most closely related to:

1. The goldfish: Chickens

2. The mouse: Humans

3. Homology is a term used to refer to a feature in two or more species that is similar because of descent; it evolved from the same feature in the last common ancestor of the species. Hence, similarity in DNA or protein sequences between individuals of the same species or among different species is referred to as sequence homology. Which two species in the tree above share greatest homology with respect to the beta globin gene?

Chimps and humans

4. A node is a branch point representing a divergence event from a common ancestor. Which two species have the most ancestral nodes (divergence events) in the tree above? Explain your answer giving the number of nodes leading to these species.

Chimps and humans have four nodes.

5. Looking at the phylogenetic tree above, which two organisms:

1. Diverged from their common ancestor most recently?

• Chimps and chickens 

2. Diverged from their common ancestor least recently?

• Chimps and humans

6. 

   Draw a modified phylogenetic tree to show how the tree above might change if the beta globin gene for a kangaroo was added to the multiple sequence alignment. 

7. It is important to understand that the phylogenetic trees you generated using bioinformatics tools are based on sequence data alone. While sequence relatedness can be very powerful as a predictor of the relatedness of species, other methods must be used in addition to sequence homology, to determine evolutionary relationships. Briefly describe 3 other methods that you think might be used to determine evolutionary relationships.

Embryology

Anatomy

Fossil Evidence