The rate of change is not identical for all genes. The following graph shows the
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Question
The rate of change is not identical for all genes. The following graph shows the rate of change of four hypothetical human proteins (A-D). Use this graph to answer the following questions. )
00 of amino 75 acid subs. per 100 residues 375 750 125 1500 Millions of years since divergence a. Which of the proteins is changing at the fastest rate? b. Which protein is most conserved? c. Which evolutionary force (Drift, Selection, or Migration) plays the biggest role in causing the observed difference in the rate of change between proteins A-D? d. You are interested in determining if the genes encoding each of these human proteins (A-D) also exist in rice. Which protein is most likely to have the highest sequence similarity to its homolog in rice? Justify your answer. e. If you were going to use one of the proteins to build a phylogenetic tree of various mammalian species (which diverged during the last 50 million years), which protein sequence would be most useful? Justify your answer. f. If you were going to use one of the proteins to build a phylogenetic tree of various plant species (which diverged during the past 500 million years), which protein sequence would be most useful? Justify your answer. g. If you were going to use one of the proteins to builda phylogenetic tree of a mixture of plant and animal species (which diverged 1200 million years ago), which protein sequence would be most useful? Justify your answer.Explanation / Answer
Ques-a: Which of the proteins is changing at the fastest rate?
The rate of change is not identical for all genes for protein coding. In the graph, it has clearly observed that the rate of amino acid substitution per time is directly proportional to the protein divergence that shows the rate of change of hypothetical human proteins (A-D). Therefore, protein A has changing at the fastest rate
b. Which protein is most conserved?
The most conserved hypothetical protein is “protein D” as per the slope of the lines on the graphs because the rate of change with amino acid substitution & the rate of change is lowest and slope is linear.
c. Which evolutionary force (Drift, Selection, or Migration) plays the biggest role in causing the observed difference in the rate of change between proteins A-D?
Natural selections is the biggest evolutionary force observed in these proteins with meticulous changes in the “differential protein expression” based on number of amino acid change per 100 residues from A to D. However, genetic drift is more pertaining to small populations with sampling errors. Gene D is associated with “higher conservative nature compared to gene A”
Ques-d: If you do Southern hybridization to determine if the genes encoding each of these human proteins (A-D) also exist in rice, which would give the strongest hybridization signal?
Answer: D: Highest sequence similarity to the homologs in rice is determined based on Southern hybridization & how genes coding for human proteins. The rate of change is lower therefore, “therefore sequence similarity is higher” for proteins. However, gene coding for protein A is different between hypothetical human protein and rice protein.
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