Evolution__3rd_Edition

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Mice do not show the same pattern
However, the third pattern in the results suggests that the first two patterns are not
simple artifacts of the method. The same analysis was performed on the available
genome sequence for the mouse. The mouse showed neither pattern a neither a burst
of Alu activity 25–75 million years ago, nor a slow down in all transposable element
activity in the past 25 million years. Thus the methods alone do not automatically generate
these patterns; but it is too early to say that the patterns are real. If the patterns are
confirmed in more rigorous analyses, they will require explanation. Why, for example,
has transposable element activity slowed down in the past 25 million years of human
evolution?
The main point here is that by identifying particular kinds of repeat sequence,
counting the differences between them, and applying a molecular clock, we can infer
the history of non-coding DNA. The particular patterns found in a preliminary analysis
are interesting, but they may not hold up in future research. In any case, some patterns
will emerge in time from the sequence data. When they do, biologists will be after an
explanation for them.
19.8 Conclusion
CHAPTER 19 / Evolutionary Genomics 569
At one level, evolutionary genomics is not so new. Biologists have been studying the
3,500 million-year history of our bodies for a century and a half, and there must clearly
be an equivalent history of our DNA as well. Biologists could have seen that the questions
of evolutionary genomics could be asked. Indeed, some modern research has
grown out of earlier ideas, such as Ohno’s “2R” hypothesis. What has changed is our
ability to answer the questions. We have more evidence, and many new techniques that
have been invented to test hypotheses with that evidence.
The examples of research that we have looked at in this chapter illustrate a new
science in that the research could not have been done much, if at all, before the year
2000. The evidence would have been lacking. The history of the human gene set
can only be inferred when we know most of the DNA sequence for several species.
Investigations of the timing of duplications, deletions, and gene transfers, require
sequence data. The history of the human sex chromosomes could not be reconstructed
until we had sequences for the coding parts of the X and Y chromosomes. The results
we have seen in this chapter are more provisional than the results in much of the rest of
this book. However, evolutionary genomics is worth looking at as much for its promise
as for its achievements so far a interesting thought the initial results are. Evolutionary
genomics is likely to be one of the fastest growing areas of evolutionary biology in the
coming years.