DNA is a long fiber, like a hair, only thinner and longer. It is made from two strands that stick together with a slight twist. Proteins attach to the DNA help the strands coil up into a chromosome when the cell gets ready to divide.
The DNA is organized into stretches of genes, stretches where proteins attach to coil the DNA into chromosomes, stretches that “turn a gene on” and “turn a gene off”, and large stretches whose purpose is not yet known to scientists.
The genes carry the instructions for making all the thousands of proteins that are found in a cell. The proteins in a cell determine what that cell will look like and what jobs that cell will do. The genes also determine how the many different cells of a body will be arranged. In these ways, DNA controls how many fingers you have, where your legs are placed on your body, and the colour of your eyes.
Difference between DNA and a Chromosome?
A chromosome is made up of DNA and the proteins attached to it. There are 23 pairs of chromosomes in a human cell. One of each pair was inherited from your mother and the other from your father. DNA is a particular bio-molecule. All of the DNA in a cell is found in individual pieces, called chromosomes. This would be like muffins. Muffins are made up of muffin-matter and paper cups. All of the muffin-matter in your kitchen is found in individual pieces, called muffins.
So, why do you want to learn about DNA?
If you have gotten this far, you already have some curiosity about DNA. That curiosity may have come from hearing about it in the news or in the movies. A revolution has occurred in the last few decades that explains how DNA makes us look like our parents and how a faulty gene can cause disease. This revolution opens the door to curing illness, both hereditary and contracted. The door has also been opened to an ethical debate over the full use of our new knowledge. In the end, curiosity is the reason to learn about DNA. Fittingly, curiosity is the driving force behind science itself.
There have been two main types of forensic DNA testing. They are often called, RFLP and PCR based testing, although these terms are not very descriptive. Generally, RFLP testing requires larger amounts of DNA and the DNA must be undegraded. Crime-scene evidence that is old or that is present in small amounts is often unsuitable for RFLP testing. Warm moist conditions may accelerate DNA degradation rendering it unsuitable for RFLP in a relatively short period of time.
PCR-based testing often requires less DNA than RFLP testing and the DNA may be partially degraded, more so than is the case with RFLP. However, PCR still has sample size and degradation limitations that sometimes may be under-appreciated. PCR-based tests are also extremely sensitive to contaminating DNA at the crime scene and within the test laboratory. During PCR, contaminants may be amplified up to a billion times their original concentration. Contamination can influence PCR results, particularly in the absence of proper handling techniques and proper controls for contamination.
PCR is less direct and somewhat more prone to error than RFLP. However, PCR has tended to replace RFLP in forensic testing primarily because PCR based tests are faster and more sensitive.
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