Genetic Technologies. New applications, new ethical issues. DNA Fingerprinting. DNA Fingerprinting. Used in a wide range of areas, from forensics to medicine to taxonomy, to analyze DNA.
The samples are then loaded into a gel (usually agarose or polyacrylamide)
Different fragments have different molecular sizes, so move at different rates through the gel. Because they are polar molecules, they move in response to the electrical field across the gel.
At this point, the gel could be stained, photographed, and discarded. For finer analysis, such as locating specific segments of interest the gel may be placed on a nylon fiber pad, and the DNA fragments driven into the pad using a downward-directed electrical current.
Labeled DNA probes designed to bind to segments of interest are loaded onto the pad. These may be tagged with radioactive phosphorous or fluorescent dye.
Probes stick to the segments of interest, such as known STRs or specific forms of a disease-causing allele.
The resulting DNA fingerprint can then be analyzed by the experts. The segment above, for example, shows DNA from the same region for 13 different people. It could be used to determine who was at a crime scene, or identify a child’s real parents.
1. The microarray is designed with probes that will bind to specific loci.
3. mRNA is used to synthesize cDNA, which is tagged with fluorescent dyes.
4. The cDNA is applied to the microarray and allowed to hybridize with the probes.
6. A machine scans the microarray with red and green laser light, making the probes fluoresce, and photographs the results.
5. The microarray is washed to remove cDNA that did not stick.
The results are analyzed to determine which genes are being expressed in specific cells, and which are turned off.
The differing brightness of the fluorescence also tells researchers how much mRNA is being generated by each of the genes that is active.
Researchers might, for example, compare gene expression in normal cells and cancerous cells to see which genes are active in cancer cells that are not in normal cells, and which genes are supressed in cancer cells.
Here, a gene is prepared for insertion into a DNA plasmid from a bacteria, which will be used to insert the gene into a plant cell.
The enzyme ligase seals the ends of the trans gene into the bacterial plasmid.
Plasmids are applied to a culture of bacteria that are known to infect plant cells.
This particular bacteria attacks by inserting plasmids into the plant host cell. Now it inserts the plasmid containing the trans gene.
If all goes well, some of the cells will incorporate the trans gene into their own DNA, where it will be expressed.
The transgenic cells are treated with plant hormones to grow new plants, and the plants are tested for the expression of the gene.
Dolly began life as a single cell from one breed of sheep, a white-faced Finn Dorset.
An egg of a Scottish Blackface ewe was harvested and its nucleus removed.
The two cells were stimulated with an electrical pulse to unite. This also stimulated mitosis. The egg cell carried on with multiple cell divisions as though it had been fertilized.
The embryo was implanted into the uterus of a Blackface ewe. Some months later, she gave birth to the white-faced lab, Dolly.