Hello,

With 30X depth NGS sequencing, what is the chance at one position that an allele is not sequenced at all with 30 reads ?

Should we do 2^30 = 1 073 741 824 ?

Thank you.

Calculate the chance that an allele is not sequenced?

0

Entering edit mode

3 months ago

vpsev3
▴
10

Hello,

With 30X depth NGS sequencing, what is the chance at one position that an allele is not sequenced at all with 30 reads ?

Should we do 2^30 = 1 073 741 824 ?

Thank you.

3

Entering edit mode

3 months ago

Fabio Marroni
★
2.8k

The probability is a number between 0 and 1, so by definition it cannot be 2^30. However, I think you were close.

First of all: I assume you want to know the probability that, in a heterozygous individual, sequencing 30 reads, you always sequence allele 1 and never allele 2.

Each read has a 0.5 probability of sequencing allele 1, and 0.5 of sequencing allele 2. The probability that with 2 reads you always sequence allele 1 is 0.5 * 0.5 (0.5^2), with 3 is 0.5^3, and so on... thus the probability that with 30 reads you always sequence allele 1 is 0.5^30, i.e. 9^-10.

I hope this helps

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Or is the probability just 1 in 30?