Genome Sequencing

Question 1

Outline the steps involved in sequencing the genome of an organism

Answer 1

• genomes are first mapped to identify which chromosome or section of chromosome they have come from
• samples of the genome are then sheared into smaller sections (shot gun approach) using restriction enzymes
• these DNA fragments are then inserted into BACs (bacterial artificial chromosomes), each fragment is inserted into a different BAC
• the BACs are then transferred to E.coli and as the cells grow in culture many copies of the sections are produced (clone libraries)
• the DNA is then extracted from cells containing specific BACs and cut into smaller fragments using restriction enzymes
• each copy is cut with a different restriction enzyme so this gives different fragment types
• the fragments are then separated using gel electrophoresis
• each fragment is then sequenced using an automated process (Sanger sequencing)
• computer programmes then compare overlapping regions from the cuts made by different restriction enzymes in order to reassemble the whole BAC segment sequence

Question 2

Define the term genome

Answer 2

The entire genetic code in the cells of a single species

Question 3

Explain how gene sequencing allows for genome wide comparisons between individuals and species

Answer 3

• can be used to ascertain how important the gene is
• work out evolutionary relationships - the more similar the sequence the more closely related the species
• compare the genome of a pathogenic organism with that of a similar non- pathogenic organism - enables us to find out what genes are important in causing a disease
• identify genes which cause inherited diseases
• investigate the effects of specific mutations by manufacturing a mutation and inserting it into a microorganism