Junk DNA…Trashed Again


Repetitious "words" in DNA represent more than half of the human genome's three billion nucleotides.1 Because human reasoning essentially views the repetition of words in spoken languages as errors, these DNA sequences were first written off as meaningless junk. Secular scientists assumed that natural processes somehow produced the repeats over eons of evolution through accidental duplications and that these accidents were carried along in the genome as useless baggage. Now it appears nothing could be further from the truth since these repetitive words are linked with pervasive biochemical function.1

One class of repetitious human genome sequences recently highlighted in the news is called tandem repeats (TRs). These are simply stretches of DNA comprised of two or more contiguous copies of a "word" (called a motif) arranged in a head-to-tail pattern. For example, the TR "ttacttacttacttacgttac" is simply a repeat of the four-base motif "ttac" five times. Amazingly, these TRs are found all over the human genome: inside genes, outside genes, and even inside the protein-coding regions of genes. Among individual humans, many TRs vary in the length of the repeat. They have been used in forensics as highly effective DNA markers to solve criminal and paternity cases.

Despite knowing about these TR sequences and using them as reliable genetic markers, scientists have known very little about their actual function. Historically, anomalies like these repeating sequences, that seem to make little sense upon first glance, were often relegated to the trash bin of "junk DNA."

However, one group of researchers recently took a different approach and hypothesized that these sequences may have a purpose. They developed a set of experiments to test the effect of TRs on gene expression and the epigenetic modification of DNA. Epigenetic modification is the addition of molecular tags to the DNA molecule without changing the actual DNA sequence. The result is altered gene expression.

As a consequence of extensive testing using both existing and newly generated data sets, the researchers proclaim, "Our results suggest that there are potentially thousands of TR variants in the human genome that exert functional effects via alterations of local gene expression or epigenetics." They also state,

Our study assigns biological significance to TR variations in the human genome, and suggests that a significant fraction of TR variations exert functional effects via alterations of local gene expression or epigenetics. We conclude that targeted studies that focus on genotyping [genetic testing] TR variants are required to fully ascertain functional variation in the genome.1

These new data confirm a variety of previous studies that uncovered evidence of the functional role of TRs from their association with human diseases. As it turns out, several dozen heritable human diseases are directly associated with large repeat expansions in either coding or non-protein-coding regions of the genome.2 Clearly, these regions are under tight genetic control. When the repeats go outside their boundaries of allowable length variation, disease may be the result.

Once more we have a glaring example of demonstrated function in the genome for something once declared non-functional merely based on the fact that scientists didn't know its function—as if a lack of knowledge and understanding could somehow provide an adequate answer.

If a design-based approach were more widely taken during the course of genomic discovery, just think how much improvement would take place in our understanding of currently unknown features. Such an approach would also give glory to our great omnipotent Creator who is the Master Designer and Engineer of all life.

References

  1. Quilez, J. et al. 2016. Polymorphic tandem repeats within gene promoters act as modifiers of gene expression and DNA methylation in humans. Nucleic Acids Research. 44 (8): 3750-3762.
  2. Gemayel, R., M. D. Vinces, M. Legendre, and K. J. Verstrepen. 2010. Variable tandem repeats accelerate evolution of coding and regulatory sequences. Annual Review Genetics. 44: 445-477.

*Dr. Tomkins is Director of Life Sciences at the Institute for Creation Research and earned his Ph.D. in genetics from Clemson University.

Article posted on May 26, 2016.