Question

2. How many human genome equivalents are in 20 ng of cfDNA?

3. Investors have poured over 1 billion dollars into a company called “Grail” that promises ultra-sensitive early detection of cancer from one drop of blood. We routinely extract 20 ng/of cfDNA from 4 mLs of plasma. Assume one drop of blood has 40 ul of plasma. How many human genomes worth of cfDNA are in this one drop? Are claims they can detect one cancer genome among 10,000 normal cfDNA genomes well-founded?

4. Our qPCR standard is at 0.1 ng/uL. For the first qPCR standard dilution, we take 10uL of the qPCR standard and add it to 90uL TT buffer. How is this equivalent to 5000 GEs? (Note: the qPCR standard is a dilution of our LPA)

Answer 1

2. How many human genome equivalents are in 20 ng of cfDNA?

Ans: Since 3.59 x 10-3 ng of DNA  = 1 Genome equivalent (GE)

Therefore 20 ng of cfDNA = 1/3.59 x10-3ng DNA x 20 ng of cfDNA

20 ng of cfDNA = 5571 Genome equivalents (GEs)

3. Investors have poured over 1 billion dollars into a company called “Grail” that promises ultra-sensitive early detection of cancer from one drop of blood. We routinely extract 20 ng/of cfDNA from 4 mLs of plasma. Assume one drop of blood has 40 ul of plasma. How many human genomes worth of cfDNA are in this one drop? Are claims they can detect one cancer genome among 10,000 normal cfDNA genomes well-founded?

Ans: 4ml (4000) ul of plasma = 20 ngof cfDNA

40 ul of plasma = 4000ul /40ul x 20 ng of cfDNA

40 ul of plasma = 0.2 ngof cfDNA

Since the weight of human genome = 3.59 x 10-12 grams (weight of human genome = 3.59 x 10-3 ng)

Therefore number of human genomes in 0.2 ng of cfDNA = 0.2ng/3.59 x 10-3 ng

number of human genomes in 0.2 ng of cfDNA = 55.7

4. Our qPCR standard is at 0.1 ng/uL. For the first qPCR standard dilution, we take 10uL of the qPCR standard and add it to 90uL TT buffer. How is this equivalent to 5000 GEs? (Note: the qPCR standard is a dilution of our LPA)

Ans: Since 3.59 x 10-3 ng of DNA  = 1 Genome equivalent (GE)

Therefore 20 ng of cfDNA = 1/3.59 x10-3ng DNA x 20 ng of cfDNA

20 ng of cfDNA = 5571 Genome equivalents (GEs)