Genetic Linkage

“Genetics is the study of biologically inherited traits” (Hartl & Jones, 2006, p.2). Every species has specific traits and characteristics that set them apart from another species. With the advances in science today, people can actually predict the probability of dominant or recessive genes being apparent in offspring. A genetic map is a diagram used to show the arrangement of genes and the distance between them. The reason this is important is because genetic distance derives from the probability of recombination between genes.

One popular mapping technique is called linkage. Linkage is a method that helps to point out whether certain sections of chromosomes have a high or low probability of having a risk gene, and what the frequencies of the possibilities are. In linkage studies, researchers look for a marker that is consistently present in people with the condition being studied. When a marker is found, the marker and the gene causing the condition are said to be linked (What is, 2007). The problem with these studies is that you don’t just test DNA from family members, but you need DNA from others as well.

To put things in perspective, take a look at Down Syndrome. Down Syndrome is a disorder that affects the nervous system, and does so because it has an extra Chromosome 21. Its markers include echogenic intracardiac focus, short femur and humerus measurement, hyperechogenic bowel, thickened nuchal skin fold, and fetal hydronephrosis (Markers for Down). When a blood test comes back as there being a potential for Down Syndrome, along with one of these markers, concerns are elevated because of the linkage between Down Syndrome and these particular markers.

References

Hartl, D.L. & Jones, E.W. (2006). Essential Genetics: A Genomics Perspective. (4th ed.). Sudbury, Massachusetts: Jones and Bartlett Publishing.