Applications of Genetics

Question 1

What was the Human Genome Project?

Answer 1

A project that ran from 1990 to 2003 to determine the order of bases in the human genome as well as the identify some genes, their sequencing and loci.

Question 2

What sequencing was used in the Human Genome Project and what were the disadvantages?

Answer 2

Sanger Sequencing which sequences relatively small sections of DNA at a time (usually <1,000 bps) so took a long time.

Question 3

What was the 100k Genome Project?

Answer 3

A project launched in 2012 and completed in 2018 to sequence 100 000 genomes from patients with cancer/rare disease and members of their families.

Question 4

What sequencing was used in the 100k Genome Project?

Answer 4

Next Generation Sequencers (NGS), which can sequence an entire genome in just a few hours.

Question 5

What are the ethical issues with the ownership of genetic information after sequencing?

Answer 5

Potential discrimination, social stigmatisation and misuse of the data (for example by insurance companies or employers)

Question 6

Why have we sequenced the mosquito genome?

Answer 6

Both mosquito and plasmodium genomes have been sequenced to develop better ways of controlling malaria, eg developing chemicals that could overcome insecticide resistance

Question 7

What is a stem cell?

Answer 7

A stem cell is an undifferentiated cell capable of dividing to give rise to cells which can develop into different types of specialised cells.

Question 8

What is gene therapy?

Answer 8

Treating a genetic disease by inserting a functional DNA sequence to replace a faulty allele

Question 9

What are the two types of gene therapy?

Answer 9

Somatic cell therapy and germ line gene therapy (in an embryo or gamete)

Question 10

How can DMD be treated with exon skipping?

Answer 10

The patient is given a drug which is an mRNA patch, that binds to the exon of mRNA which contains a stop codon. This creates a slightly shorter, but still functional dystrophin protein

Question 11

What are the advantages of somatic gene therapy?

Answer 11

Relief of symptoms with no need to take medication, could prevent the development of cancer, does not permanently change the genome so any negative effects would not be inherited

Question 12

What are the disadvantages of somatic gene therapy?

Answer 12

More than one treatment usually required, difficult to get the gene to integrate into the chromosome and function correctly, genetic disorder can still pass to offspring, long term effects unknown, could be an immune response if using a virus as a vector

Question 13

What are the advantages of germ line gene therapy?

Answer 13

Children could be born free from genetic diseases, the diseases could be completely eradicated

Question 14

What are the disadvantages of germ line gene therapy?

Answer 14

Could open the door to modifying the characteristics of a child, raises difficult moral, ethical and social issues, could create new disease (such as leukaemia)

Question 15

What is genetic engineering?

Answer 15

Taking a gene from a donor organism and inserting it into the DNA of a recipient organism

Question 16

What are transgenic organisms?

Answer 16

Organisms which contain DNA from another organism

Question 17

What is recombinant DNA?

Answer 17

DNA formed by joining sections of DNA from 2 different sources

Question 18

What are the steps in genetic engineering?

Answer 18

1. Obtain the required gene 2. Insert this DNA fragment into a vector (virus/plasmid) 3. The vector carries the gene into a suitable host cell 4. The recipient expresses the gene 5. Identification of the host cells that have taken up the gene by the use of gene markers 6. Growth of the transformed host cells

Question 19

What are the three methods for obtaining the gene as a DNA fragment in genetic engineering?

Answer 19

Use restriction endonucleases to cut the DNA at palindromic sequences. Use reverse transcriptase to synthesise cDNA from mRNA. Use an automated polynucleotide sequencer to construct the gene

Question 20

What are the advantages of using reverse transcriptase over restriction endonucleases?

Answer 20

You do not have to locate the gene on the chromosome, restriction enzymes will not cut the DNA into non functional fragments, mRNA has already been spliced so will not contain introns

Question 21

Once you have obtained the gene, which enzyme do you use to join it to the plasmid vector?

Answer 21

DNA ligase, which joins the sugar phosphate backbone of DNA in a condensation reaction

Question 22

What are sticky ends?

Answer 22

Short sequences of unpaired DNA bases created when using restriction enzymes

Question 23

How do you make a DNA copy of a gene from the mRNA?

Answer 23

Obtain the mRNA from cells that are actively producing the protein, convert it into cDNA (single stranded DNA) using the enzyme reverse transcriptase. Use DNA polymerase to convert it into double stranded cDNA

Question 24

How do you identify which bacteria have been successfully transformed in genetic engineering?

Answer 24

Use genetic markers such as antibiotic resistance genes. Insert the donor gene into the middle of one of these genetic markers. Then use replica plating to identify the bacteria that have successfully taken up the recombinant plasmid

Question 25

What are the advantages of using genetically engineered bacteria to synthesise proteins?

Answer 25

There is no limit to the amount of protein that can be synthesised. The complicated structure of many proteins cannot be synthesised except by living cells. No need to extract proteins from mammalian organs (issues of disease).

Question 26

What are the disadvantages of using genetically engineered bacteria to synthesise proteins?

Answer 26

Complicated and expensive, requires experienced staff and equipment, difficult to identify and isolate desired human genes, some proteins require >1 genes for their synthesis, not all eukaryotic genes can be expressed in prokaryotic cells

Question 27

What are the risks of using genetically engineered bacteria to synthesise proteins?

Answer 27

Antibiotic resistance genes used as markers in plasmids could be transferred pathogenic bacteria. Genes could be linked to oncogenes that might increase cancer risks

Question 28

What could be the advantages of GM crops?

Answer 28

Higher yield, superior keeping qualities and flavour, resistance to pathogens and insects, reduction of pesticide use, reduction of fertiliser use by adding N fixing genes

Question 29

What are the concerns with GM crops?

Answer 29

Dispersal of pollen to wild weed species, unknown effects of eating the new proteins, a reduction in biodiversity, organic farm produce may be compromised.

Question 30

What are STRs?

Answer 30

Short tandem repeats. Sequences of between 3-5 nucleotides that are repeated multiple times (normally between 6 and 15). Individuals inherit a different length repeat from each parent

Question 31

Why does DNA separate into bands in gel electrophoresis?

Answer 31

DNA has a negative charge. It is placed in wells near the negative electrode, so will move towards the positive electrode. The smaller the fragment the faster it moves through the gel, so smaller fragments move further in the same period of time

Question 32

How can you see the bands on an electrophoresis gel?

Answer 32

Use Southern Blotting. This uses radioactive DNA probes to attach to the complementary STRs. The gel is then blotted with nylon, and autoradiography is done to show the radioactive bands on the nylon

Question 33

What can genetic fingerprinting be used for?

Answer 33

Catching criminals and paternity testing

Question 34

How do you amplify a DNA fragment? (Produce more of it)

Answer 34

The polymerase chain reaction (PCR)

Question 35

What are the three steps in PCR and what temperatures do they use?

Answer 35

1. Break the H bonds between strands by heating to 95 degrees. 2. Anneal the primers by cooling to 55 degrees. 3. Extension. Heat to 70 degrees so DNA polymerase can synthesise a complementary strand

Question 36

What are the limitations of PCR?

Answer 36

Any contamination will also be amplified, Taq polymerase has a high error rate, it only works on short fragments, it can only be used for about 20 cycles

Question 37

Why can PCR only be used for around 20 cycles?

Answer 37

Reagent concentrations become limiting, the enzyme denatures after repeated heating, single-stranded molecules start to base pair with each other rather than with the primers.

Question 38

Why are primers needed in PCR?

Answer 38

DNA polymerase can only bind to double stranded DNA fragments

Question 39

Which polymerase is used in PCR and why?

Answer 39

Taq DNA polymerase from Thermus aquaticus. This is an extremophile which lives in hydrothermal vents, meaning the polymerase can withstand 95 degrees