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Diploid
| What it's not: |
a duck-billed dinosaur. |
| What it is: |
An organism that has two sets of chromosomes in each cell. Among the many things that we humans are, we are also diploid. We have one set of chromosomes from dad (specifically from his sperm cell) and the other from mom (effectively from her egg cell). Diploid also means that we have two alleles, whereas haploid organisms have only one. This provides more flexibility because if we get a mutation in one allele, there is often the other that can cover the workload. However, in haploid situations, once the only allele is wiped out, that function can be lost. |
DNA (Deoxyribonucleic Acid)
| What it's not: |
An acronym for Did Not Answer. |
| What it is: |
An abbreviation for deoxyribonucleic acid, the essential molecule of heredity. The twisted ladder of the base pairs (also more famously known as the double helix) of the DNA molecule contains the chemically coded instructions to construct and maintain a living organism. The specific sequence of DNA’s bases stores all the hereditary information. Interestingly or distastefully enough, bacterial DNA was first isolated in 1868 by Friedrich Miescher from the nuclei of pus cells, which were smeared, in large quantities on discarded bandages. For more detail (if you dare), see Steven Rose. The Chemistry of Life: Fourth Edition. (Toronto: Penguin Books Canada Limited, 1999.), Page 68. |
DNA Fingerprint
| What it's not: |
A permanent record of questions a student did not answer on tests. |
| What it is: |
A picture of a fragment of DNA that displays a pattern unique to its owner. As you probably know, in terms of our genetic make up we human beings are 99.9% the same. Still, there’s a world of difference between most of us and Einstein, or between most of us and Cher for that matter. After all, when you consider that there are around 3 billion base pairs in human DNA, 0.1% of that total is a mighty big number. Coupled with this, we know from genetics and from old-time popular music that “It’s the Little Things that Mean A lot”. DNA fingerprinting focuses on those ‘little things’ flagging telltale signs of our uniqueness.
The simple explanation is that a person’s DNA is cut up with enzymes, run on a gel, and the resulting bands are unique to him or her. To understand why these bands are unique, we have to flesh out the technique a bit more. First, genomic DNA is cut up with restriction enzymes. You would think that everyone would have the same sites in the same places. (We do, for the most part.) But restriction enzymes are fickle. If there is even a one base pair difference, they won’t cut. So, in someone with a change, her fragment will be longer (see b below). In someone who has a change to create a new site, his fragment will be shorter (see c). And if the restriction enzyme differences aren’t enough to determine uniqueness, there are repeat sequences that vary between people. Logically enough, these kinds of sequences are called variable number tandem repeats. For example, if one person has 4 sets of “CA” in a row (see d below), her fragment will be shorter than someone who has 11 sets (see e). And of course, restriction site changes and repeat size changes can occur in the same fragment.
a. Normal ____________________
b. Site not recognized _________________________
c. New site __________
d. Less repeats ____________CACACACA_________
e. More repeats ___CACACACACACACACACACACA___
These telltale band patterns are used in paternity tests and in forensic cases. By the way, the term DNA fingerprinting is reserved for the technique pioneered by Alec Jeffries. The newer techniques are referred to as DNA profiling. |
DNA Polymerase
| What it's not: |
A wood sealer sold in hardware stores. |
| What it is: |
An enzyme that can make new DNA strands from an old strand/template. There are several DNA polymerases in our cells; and although they have slightly different functions, they all can replicate DNA. |
Dominant
| What it's not: |
The queen of the anthill |
| What it is: |
The alleles of a gene are usually described as either dominant or recessive. The dominant allele is generally the “stronger” allele and is the trait expressed when the two different alleles are found together. For example, in the brown and blue alleles for eye colour, brown is the dominant one. So when someone has one brown and blue allele, he generally has brown eyes. For a more detailed, more accurate and more entertaining exploration of this concept that goes beyond the brown and blue, check out “Mix Those Genes”, an online game in the "DNA Basics" section of this site. |
Drug Target
| What it's not: |
A rundown house under observation by the RCMP. |
| What it is: |
We hear about drug targets all the time in genetic research into human disease. Basically, this research tries to determine where a process went wrong for a particular condition so that drugs can be designed to help the process right itself. Researchers can try to figure out the normal biological process and where things go wrong to create disease. If this normal biological process is unknown, researchers can use the fancy new technique of microarrays to compare gene expression between patients and unaffected individuals. Any differences are possible “targets” for therapy because they could indicate what’s “wrong” and causing disease.
For example, type I diabetics do not produce enough insulin, and insulin is provided to the patients so that they can lead a fairly normal life. Now, diabetes research is trying to figure out ways to avoid all the needles needed to provide the missing insulin. So researchers are trying to discover why patients don’t have enough insulin so that new targets for therapy can be developed. The treatment could be different depending on the original problem: if the cells that make insulin are destroyed, you want a therapy that protects these cells; but if you are missing the insulin gene, there needs to be a way to provide it. As you can see, the original drug target was pretty basic but as researchers learn more about diabetes, the treatments can become more and more specific to each patient. |
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