Evolution, can you please help?

Question

1. The enzyme Esterase-5 has been extracted and purified from a number of supposedly closely related fruit fly (Drosophila) species. These have been run under gel electrophoresis, to separate by overall charge. The distances the protein dots have moved down the gel are shown below. Show these data graphically. (Hint- are these discrete or continuous variables?)

Drosophila species Distance From origin to protein spot(s) mm

D. simulans 142 and 150

D. sechellia 142 and 150

D. pseudoobscura 138

D. persimilis 142 and 138

D. grimshawi 160

Questions
1) What can you deduce about the phylogeny of these flies?
2) Why do some flies appear to have two spots and others appear to have one?
3) What shortcomings in this technique are obvious from this data?

Answer 1

Esterase-5 shows protein banding at four sizes, p138, p142, p150, & p160. These may represent mutation and genetic drift producing variation among parts of the original protein sequence.

D. simulans & D. sechellia share matching protein sizes at p142 and p150 so probably share the greatest homology so may share a clade.
D. persimilis shows homology, with p142, to D. simulans & D. sechellia.
D. persimilis also shows homology to D. pseudoobscura with p138.
How close can not be determined without sequence.

D. grimshawi p160 shares no homology to the Drosophila examined so is likely to be most divergent implying an earlier split.

2) Flies with two bands may express two proteins with different, somewhat homologous sequence or subunits of the same protein. This blot should be probed for known functional or conserved sequence.
If they are two proteins at some point the Esterase gene was replicated in the fly genome allowing divergence between the two copies. The expression may now be restricted by developmental stage or tissue specificity. Tissue blots are needed to determine stages, and location of expression.

If we assume there has been a replication of the gene this is reflected in the data. D. pseudoobscura may reflect the single ancestral gene as does D. grimshawi.
p142 is shared across two clades so may be the shared replicated sequence.

Without gene sequence the degree of divergence is not determined. Homology between the paired bands seen in each of the three species D. simulans, D. sechellia, and D. persimilis is needed a well as determining if the bands are orthologs.
When comparing sequence data between bands in one species we can see is the percentage of change in the enzyme, its degree of homology. Between species the comparison is termed its degree of orthology.
The orthology between Esterase 5, and other sequenced genes, can give a more accurate basis for creating a phylogenic tree with branch length reflecting % orthology.

Answer 2

This is nothing to do with evolution - in the sense of molecules to man, Neo-Darwinian evolution.

It is Selection (Artificial rather than Natural).

Evolution requires a net increase of genetic information. The mutations above result in a net loss of genetic information, or are neutral at best.