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Genomes And Gene Technologies Notes

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Genomes and gene technologies Context Genome sequencing gives information about the location of genes and provides evidence for the evolutionary links between organisms. Genetic engineering involves the manipulation of naturally occurring processes and enzymes. The capacity to manipulate genes has many potential benefits, but the implications of genetic techniques are subject to much public debate. Candidates should be able to:

Outline the steps involved in sequencing the genome of an organism;

• DNA is extracted from cells

• The PCR is used to make many copies of the DNA.

• The DNA is cut into small lengths (mechanically and then by restriction endonuclease enzymes), which are then copied further.

• Primers (short lengths of DNA) are added which join to the 3' terminal of the DNA template strand. The primers identify the gene and allow DNA polymerase to bind.

• Nucleotides (dNTP) and enzymes are added to copy the DNA many times (using the polymerase chain reaction).

• ddNTP (fluorescently tagged) nucleotides are added (Either A*, G*, C*
or T*). When these nucleotides are added, they cause the termination of a growing chain of DNA.

• Chains of many different lengths are produced, depending on where the fluorescently labelled modified nucleotide was added to the chain.

• Electrophoresis is then carried out to sort segments by size.

• A laser linked to a computer is used to identify the shortest sequences first and thus work out the sequences of bases.

• Computers can also work out long sequences of DNA from shorter overlapping sections.

Outline how gene sequencing allows for genome-wide comparisons between individuals and between species (HSW7b); Between species:

• Evolutionary relationships can be explored by considering the similarities in the genomes of two species

• The identification of genes common to most/all living things can give clues as to the relative importance of these genes to life

• Gene interaction can be researched: each the control of developmental genes by the homeobox sequence… the homebox genes for

bodyplans in humans are very similar to those in flies- indicating a common ancestor.

• Medical research can be carried out, by comparing the genome of pathogenic and non- pathogenic bacteria, to identify the genes responsible for causing disease. Between individuals

Early human migration can be mapped by comparing the genomes of humans from around the world

Medical advances can be made by possibly producing drugs specific to an individuals genome, to maximize its effect

The genetics of human diseases can be studied, so that we may predict whether someone has inherited a specific genetic disorder.

Define the term recombinant DNA. DNA made by genetic engineering. Joining together pieces of DNA from two or more different sources.

Explain that genetic engineering involves the extraction of genes from one organism, or the manufacture of genes, in order to place them in another organism (often of a different species) such that the receiving organism expresses the gene product (HSW6a); The required gene is isolated…
1) The mRNA can be extracted and reverse transcriptase [from viruses] to synthesise DNA. 2) Or, the gene can be synthesised in a polynucleotide sequencer. 3) Or… A DNA probe can be used to locate the gene on a length of DNA and restriction enzymes can be used to cut the required length.
…From one organism and the gene is transferred to a vector (e.g. a bacterial plasmid or using a virus). The vector is then used to transfer the gene to the recipient cell of another organism.

Describe how sections of DNA containing a desired gene can be extracted from a donor organism using restriction enzymes; Restriction enzymes are a group of enzymes used to cleave, or cut, DNA strands. They each have a characteristic base sequence at which it cleaves (restriction site). There are over 50 commonly used restriction enzymes. They were originally extracted by bacterial cells. In bacterial cells they carry out

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