Molecular Genetics (Keith Edwards 19-22)

Question 1

How can CRISPR-Cas9 be used for targeted gene editing?

Answer 1

• It functions as the prokaryotic ‘immune system’ when viral DNA infects it, RNA is produced which is complementary to the viral DNA, this acts as a guide for Cas9 nuclease to cleave the viral DNA, making it ineffective.
• This can be utilised by scientists; we can change the small guide RNA (sgRNA) to match its target.
• The enzyme locks onto a PAM sequence (upstream of the target DNA).
• Cas9 causes double-strand breaks of the target DNA (thanks to the sgDNA).
• A new DNA template strand (e.g. healthy gene) can then be incorporated into the target DNA, replacing the original sequence.
• leaves no trace of genome editing…

Question 2

How can the Hagberg falling number test (HFN) be used to determine which wheat is good for baking?

Answer 2

• the falling number is the time is taken (secs) for a stirrer to fall through a hot slurry of ground wheat.
• the greater the amount of alpha-amylase, the thinner the starch, and the quicker the time.
• Ideal baker’s wheat should have a high HFN as it contains more starch (less alpha-amylase)

Question 3

What is preharvest sprouting (PHS)?

Answer 3

• When grain germinates on ears of wheat - occurs when late summer is hot and wet and wheat is tricked into germinating.
• underpinned by VP1 gene. The VP1 transcription factor represses genes encoding for hydrolytic enzymes associated with germination such as alpha-amylase.
• no mutation in the VP1 gene but a wetter summer = more alternative splicing (not sure why)

Question 4

What is significant about cytosine in pluripotent cells and unipotent cells?

Answer 4

• In pluripotent cells, cytosine is in its native state, whereas in unipotent cells, more cytosine is methylated.

Question 5

What are euchromatin and heterochromatin?

Answer 5

• euchromatin is more acetylated, whereas heterochromatin is much more tightly packed due to methylation.

Question 6

What does the experiment with Agouti mice suggest about diet and gene expression?

Answer 6

• mother was fed with high proportions of methyl donor-rich food. Her offspring were slender, brown and had longevity.
• homozygous agouti yellow = lethal
• methyl groups appeared to attach to the chromosomes of unborn mice, switching off the gene for agouti hair colour.
• Imagine if we could cure genetic diseases by altering diets!

Question 7

Tell me about the Hongerwinter of 1944 and its significance.

Answer 7

• German army blocked food to the Dutch in the winter of 1944.
• Children born at this time had stunted growth, depression, anaemia etc.
• When women living in this time had children 30 years later, some children had the same problems, despite being conceived and born in normal times.
• Does environment have a hereditary genetic effect?