Objectives: Outline the steps involved in sequencing the genome of an organism. Outline how gene sequencing allows for genome wide comparisons between individuals and species.

Uses of DNA Technology DNA Profiling (Genetic Fingerprinting) – used in forensic crime scene analysis and maternity/paternity testing Genomic Sequencing and Comparative Genome Mapping – used in research into the functions of genes and regulatory DNA sequences Genetic Engineering – used in the production of pharmaceutical chemicals, genetically modified organisms and xenotransplantation Gene Therapy – used to treat conditions such as cystic fibrosis.

Genomics DNA has regions of bases known as genes that code for the production of polypeptides/proteins. However, 98.5% of DNA is non-coding. In the past these sections of DNA were known as ‘junk’ DNA, but they are now thought to have important regulatory functions. Genomics is the study of genomes. The genome is the whole set of genetic information, in the form of DNA base sequences, that occurs in the cells of a particular organism.

Sequencing the Genome of an Organism It is useful to know which chromosomes genes are on, and whereabouts they are located on that chromosome. There are computer programs that can be used to analyse the sequence of genes on a chromosome. However, they cannot sequence one whole chromosome at a time, and so we need to cut the chromosome into smaller bits for the computer program to analyse it. You need to make a map of the original chromosomes before you cut them into bits, so that you can piece together the analysis of all the cut sections in the correct order for each chromosome. You can imagine the genome map as a picture of a completed jigsaw. After the chromosomes have been cut the small sequenced sections you can imagine as the jigsaw bits. The chromosome map is made by using radioactive markers or stains that bind to various base sequences along the chromosomes.

BAC Sequencing of the Genome 1.Genome Mapping – using markers. 2.Genome is cut into sections either by mechanical shearing, or by using restriction enzymes. 3.Each section in placed into a bacterial artificial chromosome (BAC) and transferred to E. coli 4.The E. coli grows in culture making lots of copies of itself (and hence lots of copies of the gene sections. These cells are called clone libraries. 5.The DNA is extracted from the E. Coli and restriction enzymes cut it into small fragments. Different enzymes are used on different samples to give restriction fragments of different lengths – they will show overlaps with each other. 6.The fragments are separated using gel electrophoresis, then each segment is sequenced using a computer program. The computer uses the overlapping portions to build up a picture of the whole genome.

Sequencing a BAC section using overlapping fragment analysis