sequence analysis

Which read(s):

  • 1. contain either a SNP (a single nucleotide polymorphism) or a position where different members of a multi-gene family have a different base?
  • C
  • 2. doesn't have any DNA?
  • B
  • 3. is a PCR product?
  • A, B, and C.  All of three reads were obtained by sequencing PCR products, generated with the same set of primers.
The quality plots that I refer to are ... Read more
Since DNA diagnostics companies seem to be sprouting like mushrooms after the rain, it seemed like a good time to talk about how DNA testing companies decipher meaning from the tests they perform. Last week, I wrote about interpreting DNA sequence traces and the kind of work that a data analyst or bioinformatics technician does in a DNA diagnostics company. As you might imagine, looking at every single DNA sample by eye gets rather tiring. One of the things that informatics companies ( ... Read more
As many of you know, I'm a big fan of do-it-yourself biology. Digital biology, the field that I write about, is particularly well-suited to this kind of fun and exploration. Last week, I wrote some instructions for making a phylogenetic tree from mitochondrial genomes. This week, we'll continue our analysis. I wrote this activity, in part, because of this awful handout that my oldest daughter brought home last year. She presented me with an overly photocopied paper that showed ... Read more
DNA sequence traces are often used in cases where:
  1. We want to identify the source of the nucleic acid.
  2. We want to detect drug-resistant variants of human immune deficiency virus.
  3. We want to know which base is located at which position, especially where we might be able to diagnose a human disease or determine the best dose of a therapeutic drug.
In the future, these assays will likely rely more on automation. Currently, (at least outside of genome centers) many of these results are assessed by human technicians in clinical research labs, or DNA testing ... Read more
Students at Soldan International High School are participating in an amazing experiment and breaking ground that most science teachers fear to tread. Soldan students, along with hundreds of thousands of other people, are participating in the National Geographic's Genographic Project. Through this project, students send in cheek swabs, DNA is isolated from the cheek cells, and genetic markers are used to look at ancestry. Genetic markers in the mitochondrial DNA are used to trace ancestry through the maternal line and markers on the Y chromosome can be used to learn about one ... Read more
Last year I wrote about an experiment where I compared a human mitochondrial DNA sequence to primate sequences in the GenBank. Since I wanted to know about the differences between humans, gorillas, and chimps, I used the Entrez query 'Great Apes' to limit my search to a set of sequences in the PopSet database that contained gorillas, bonobos, chimps, and human DNA. A week ago, I tried to repeat this experiment and...

It didn't work.

All I saw were human ... Read more

Metagenomics is a field where people interrogate the living world by isolating and sequencing nucleic acids. Since all living things have DNA, and viruses have either DNA or RNA, we can identify who's around by looking at bits of their genome. Researchers are using this approach to find the culprit that's killing the honeybees. We're also trying to find out who else shares our bodies, and lives in our skin, in our stomachs, and other places where the sun doesn't shine. Craig Venter used ... Read more
The simple fact is this: some DNA sequences are more believable than others. The problem is, that many students and researchers never see any of the metrics that we use for evaluating whether a sequence is "good" and whether a sequence is "bad." All they see are the base calls and sequences: ATAGATAGACGAGTAG, without any supporting information to help them evaluate if the sequence is correct. If DNA sequencing and personalized genetic testing are to become commonplace, the practice of ignoring data quality is (in my opinion) simply unacceptable. So, for awhile anyway, I'm ... Read more
We have lots of DNA samples from bacteria that were isolated from dirt. Now it's time to our own metagenomics project and figure out what they are. Our class project is on a much smaller scale than the honeybee metagenomics project that I wrote about yesterday, but we're using many of the same principles. The general process is this:
  • 1. We sort the chromatogram data to identify good data and separate it from bad data. Informatics can help you determine if data is
  • ... Read more
The next time you bite into a crisp juicy apple and the tart juices spill out around your tongue, remember the honeybee. Our fall harvest depends heavily on honeybees carrying pollen from plant to plant. Luscious fruits and vegetables wouldn't grace our table, were it not for the honeybees and other pollinators. i-5b72428eaa872c6d705e8a3dfcbe8139-bee.pngLately though, the buzz about our furry little helpers hasn't been good. ... Read more

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