QN 1. As a new researcher in human genetics at the “Genomes R Us” institute you
ID: 50390 • Letter: Q
Question
QN 1. As a new researcher in human genetics at the “Genomes R Us” institute you want to extend the work of Samuel Barondes who in 1999 used 11 DNA sequence markers and genomic DNA samples from a large Costa Rican family to map a gene whose mutant alleles increase the risk of bipolar disorder to chromosome region 18q22-23. This region contains more than 100 genes. You want to undertake a project to map this gene more accurately. You have access to the genomic DNA samples from the large family in Costa Rica used in the original study, and also to modern techniques. To get funding for this study you need to make a presentation to the funding committee of your institute.
a. Briefly explain to the committee how you would map this gene today, including the techniques and materials you would use.
b. Explain how he results of your work would give a more accurate map location for this gene.
Explanation / Answer
a. Gene mapping techniques are used to identify the locus of a gene and gene distances. DNA (deoxyribonucleic acid) profiling uses the short repeated DNA sequences that do not code for amino acids and do not affect the phenotype. They are present as short repeated sequences in our genome and this repentance is characteristic of each person. Information regarding the frequency of these sequences in a population is applied.
The person is considered homozygous or heterozygous based on the number of copies of the same repeat at the same chromosomal locus on the two homologs. If both the homologs contain same number of repeating copies then the person is considered homozygous. If the number of repeating unit varies then the person is considered heterozygous.
Capillary electrophoresis is a technique used to isolate DNA fragments. Sample DNA is combined with fluorescently labelled short fragments of DNA that correspond to the parts of CODIS (combined DNA index system) STRs, this allows the complements to bind together. This is followed by PCR (polymerase chain reaction) that amplifies the genome (i.e. amplifying the all 13 CODIS markers simultaneously).
These DNA fragments are allowed pass through hair-thin tubes called “capillaries”. The fluorescent dye is now activated by applying a laser shone. Depend upon the number of amino acids preset in the fragment, the strength of fluorescence changes. For example, in case of homozygous fragments, a single tall peak is obtained, and for heterozygous fragments two short peaks are obtained, this data is presented in a electropherogram. After separation of fragments, western blotting is applied to locate the mutant gene.
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