Return to Chromosome Fusion Lesson

FAIR TESTS and MILEs
A Chromosome Fusion Extension
(Click Here for PDF copy of this and the News Release)

Much of the strength and confidence we have in good scientific hyptheses comes from these two measures.

Fair tests are observations or experiments that can be done for which the results could be consistent with the existing hypothesis, or inconsistent with it. Consistency strengthens the hypothesis, inconsistency weakens it.

MILEs (Multiple Independent Lines of Evidence) consist of two or more different kinds of evidence pointing to the same conclusion.

Study the two ape chromosomes that appear to have fused to form our #2 chromosome, based on the matching banding patterns. This alone provides a strong indication of the source of our #2 chromosome, but there are at least two fair tests that could be done that could confirm or weaken that hypothesis:
1. Is there evidence of the typical tandem repeats (found in telomeres) located in the region of expected fusion?

When you looked for this, what did you find? _________________________________________

2. Does the position of the centromere in our #2 chromosome coincide with its position in the corresponding ape chromosome?
When you look for this, what do you find? ___________________________________________

There is at least one more test that you could look for that could confirm, or weaken, the argument for chromosome fusion. What is it?
3.

 

When we look for this, what do we find? ___________________________________________________

In a National Institutes of Health (NIH) News Release published 6 April 2005, announcing a study to be published in the 7 April 2005 issue of Nature, the following information was presented:

A detailed analysis of chromosomes 2 and 4 has detected the largest "gene deserts" known in the human genome and uncovered more evidence that human chromosome 2 arose from the fusion of two ancestral ape chromosomes, researchers supported by the National Human Genome Research Institute (NHGRI), part of the National Institutes of Health (NIH), reported today.

In the latest analysis, researchers searched the [human #2] chromosome's DNA sequence for the relics of the center (centromere) of the ape chromosome that was inactivated upon fusion with the other ape chromosome. They subsequently identified a 36,000 base pair stretch of DNA sequence that likely marks the precise location of the inactivated centromere. That tract is characterized by a type of DNA duplication, known as alpha satellite repeats, that is a hallmark of centromeres.

The complete News Release can be seen at: http://www.genome.gov/13514624 (or it may be provided by your teacher). Read the News Release, and answer the following questions:

How would you describe the effect of these Fair Tests on our original conclusion? __________________
(strongly supportive, mildly supportive, not clear, slightly weakened, very weakened)

How many MILEs do we have favoring chromosome fusion as the source of our #2 chromosome? ______

What does all of this tell you about human ancestry, and how does it affect your confidence in this?