DNA testing on sperm

[Pugdaddy]

Since sperm only carry one set of chromosomes, put together randomly from the two sets of the donor's parents, how many sperm would you need to be sure that all the genetic material is present in each of the two sets of chromosomes of the donor?

Reason I am asking is that I breed Pugs. We have a susceptability test for Pug Dog Encephalitis. Works great for live dogs as it is just send a cheek swab in and you get your answer. There are frozen straws of dogs that have long passed on. I would like to know if these deceased Pugs are carrying the susceptable genes. Each straw contains about 5 million sperm.

[Mr Monkeybat]

If we look at an individual chromosome half each sperm has a 50% chance of carrying it like the flip of a coin. If you flip 2 coins there is a 25% chance of getting 2 heads in a row a 25% chance of getting 2 tails in a row and a 50% chance of getting both. After 3 coin flips the chance of getting only one side decrease to 25% and the chance of getting both increase to 75%. The probability of getting just one side of the coin continues to half with each successive coin fiip.

 

Number of coin flips/sperm, Chance of just getting one side of coin/chromosome:

1, 1 in 1

2, 1 in 2

3, 1 in 4

4; 1 in 8

5, 1 in 16

 

11, 1 in 1,024

21, 1 in 1,048,576

31, 1 in 1,073,741,824

 

Of course dogs have 78 chromosome pairs so so if you are not testing for a singe gene but want to catch every single chromosome the chance of one chromosome being missing increases, and this is where my knowledge on statistics get a little more fuzzy.There is also the factor that a large proportion of sperm are defective and may have missing chromosomes.

[CharonY]

DNA tests generally involve the amplification of diagnostic loci via PCR. These methods are very sensitive and considering the pool of DNA a single straw should have more than enough material to detect whether any of the chromosomes carry the allele in question.