Genes & Polypeptides: Skills
Use of databases to identify the locus of a human gene and its polypeptide product
- Following the sequencing of the whole human genome, we now know the exact locus (position) of every gene across the 23 pairs of chromosomes
- Online databases have been built that are able to locate any known gene or allele
- Anyone can access these loci
- One example is the European Molecular Biology Laboratory database (EMBL)
- Examples of genes that can be located are
- The CFTR protein, critical to cystic fibrosis, on chromosome 7
- HBB, a faulty allele of which is the cause of sickle-cell anaemia, on chromosome 11
- If we know the locus of a particular gene, medicine can establish the location of a faulty allele, which is often recessive
- A faulty allele can be cut out of the chromosome by genetic engineering using recombinant DNA technology
- Replacing a faulty allele could lead to genetic therapy
- Location databases of cancer-related genes are often vital information to researchers, doctors and patients involved in cancer genetics
Databases can be used to find and compare information about DNA, mRNA and protein sequences diagram
The use of databases to compare base sequences (and protein sequences) between species
Worked example
- Let's take the example of the gene that has a mutated version that causes cystic fibrosis, called CFTR
- The location of this gene, which can be searched for in the database, is 7q31.2
- The 7 represents the fact it is found on chromosome 7
- The q represents the fact it is found of the long arm of the chromosome, which is called q
- The short arm is p
- 31.2 represents how far away the gene is from the location of the centromere of the chromosome
- The smaller the number, the closer it is to the centromere
- We can compare this information to another gene, which encodes a protein that helps with blood clotting, coagulation factor X. If this gene is mutated it can lead to haemophilia
- The location of the coagulation factor X gene is 13q34
- This is found on chromosome 13
- A conclusion that can be made about these two genes is that they are found on different chromosomes and so their inheritance is not linked
- Remember that when genes are located close together they are likely to be inherited together due to autosome linkage
- For example, a gene located at 3p24.1 is not going to be linked to a gene at 6q13.2 because they are found on different chromosomes
- However, a gene located at 3p24.1 is likely to be linked to a gene found at 3q27.8, and even more likely to be linked to a gene found at 3p18.9, because they are not only on the same chromosome, but on the same arm of the chromosome and located close together (a similar distance from the centromere)
Examiner Tip
You may be asked to compare this data in an exam and comment on the likelihood of linkage.
