Question

1.How are DNA microarrays used to diagnose disease?

2.How does gene therapy work?

3.What things have held back more extensive use of gene therapy (why doesn’t everyone with a genetic disease get treated with gene therapy?

3. What is an STR and what is useful for?

Answer 1

Question 1

Answer: DNA Microarray is a chip that contains collection of small DNA sequence called probes which are spotted on a solid surface. Each spot contain a probe that represents a gene and DNA chips that contain all the human gene are available. DNA chips that contain probes for a specific diseases are used in disease diagnosis. It is used to quantify the expression of large number of genes across many samples to diagnose the disease and to determine the effect of certain treatment etc.,. In this method, RNA is first isolated from the healthy and diseased individuals. RNA is converted to cDNA that is labeled with fluorescent molecules. cDNA from healthy and diseased individual is Labeled with different fluorescent labels (Red and Green) for identification. After labelling, the sample will be hybridized to the DNA chip that contain disease specific probes and analyzed for fluorescent signal. As the genes in the individual have complementary sequence to probes, they hybridizes to probe and produce a signal. The intensity of signal produced on each spot is directly proportional to the amount of DNA in the sample that is binding to the probes in that spot. If a gene is highly expressed, the amount of that gene will be high in the sample and more amount of this gene will bind to complementary probe to produce more signal. If a gene has low expression, the amount of that gene will be less in the sample and less amount of this gene will bind to complementary probe and produce less signal. Disease are mostly occur due to change in the metabolism particular at gene level. In healthy individual all the genes are expressed in a controlled manner, whereas in disease condition, some gene called as disease related gene may express in high amount or in low amounts, leading to diseases. DNA Microarray diagnose the disease based on the expression of these disease related genes.