To find the position of specific gene, we should first draw a map to locate it, This map can be painted using chemicals to stain chromosomes and then we can see how distinctive patterns appears, this method is called Cytogenetic Location. There is also other way to make this map, a Molecular Location method, it is a sequence of DNA building blocks to precise locate a gene on a chromosome.
A particular band on a stained chromosome normally indicates the position of a gene´s cytogenetic location, for example:
A range of bands can also indicate a gene location when the exact location is less know.
17q12 – q21
An gene´s “address” is written whit letters and numbers and have many parts that help describe it.
· The first part is a letter or a number that indicates the Chromosome number where the gene can be found. from 1 to 22 (the autosomes) or X or Y for sex Chromosomes.
· The second part is the arm where the gene is located, each chromosome has two arms, one longer arm that is called q and the short one is called p, so
if the gene is located in chromosome 1 long arm, we write 1q and if it is located in the short arm of the sex chromosome we write Xp.
· The place where the two arms of the chromosome are narrowed is called the centromere and the position of the gene increase from this point if the stained band (dark or light) is far from it. Example 14q21 is closer to the centromere that 14q22.
When a gene is located almost in the centromere or if it is very close to the end of the chromosome, there are abbreviations like “cen” when is near centromere and “ter” when is at the end.
There are many forms and methods to interpret the sequence of the human genome to find a gene’s molecular address. A sequence of base pairs of each chromosome determinate by the genome project, (an international research effort completed in 2003) is used to locate genes, hence this method is more precise it also gives small variations on the results.
admin January 14th, 2014
Posted In: Handbook