Phylogenic Trees/ Natural Evolution/ Selective Pressure evolution?? PLEASE HELP!!!?

I'm kind of confused on this question. Could someone please help me out. Thanks



Consider a DNA sequence that evolves neutrally versus one that experiences strong selective pressures. Which type of sequence would be more useful for a phylogenetic comparison of a plant and an animal? Which type of sequence would be more useful for a phylogenetic comparison of a spearmint plant and a peppermint plant?

Phylogenic Trees/ Natural Evolution/ Selective Pressure evolution?? PLEASE HELP!!!?
Generally, neutral variation is better for comparing closely related species, while selective variation gives more insight on the relatedness among more distant species.



Use the neutral variation for the spearmint and peppermint plants. Since mutations in areas that don't undergo selective pressures occur at more or less a constant rate, you can use the number of differences in such neutral regions to determine about how long ago the two species differentiated.



The region under strong selective pressures should be used for comparisons of the plant and the animal. There are many homologous regions in the genome - that is, because there are many similar processes that must occur for life to continue, we find genes coding for similar proteins. An example would be the gene for DNA polymerase or for ribosomes, since all eukaryotic cells employ these methods. They're called homologous regions because they came from a single common ancestral gene.



Since such regions are derived from a sort of base model, we can use the differences in these regions to determine about how related the organisms are. More sequence differences = less related. That's because the species would choose for slightly different variations in the gene sequence based on what was most advantageous in their particular niche.

elaine