Are all sperm the same?
July 6, 2012 2:36 PM   Subscribe

One of my sperm contains 37.5MB of DNA information in it. Does every single one of my sperm have the very same identical 37.5MB of information?

It is said that they sequenced the human genome of Craig Venter, is that exact same information inside every single one of his sperm?

If I have sex with a woman (yeah right) and birth a son, then later have sex with the same woman and birth another son, the sons will look very different when they grow up. Where does the "mutation" begin to occur?
posted by shipbreaker to Technology (18 answers total) 4 users marked this as a favorite
No. Gametes are haploid cells.
posted by supercres at 2:37 PM on July 6, 2012 [3 favorites]

Sperm only contains half a person's DNA, and that half is determined by meiosis. It's different every time.
posted by Jehan at 2:38 PM on July 6, 2012 [2 favorites]

No. They are all different from the get-go.
posted by ROU_Xenophobe at 2:38 PM on July 6, 2012 [1 favorite]

It is not the same identical 37.5MB; each sperm is a slight variation, which indeed is how come non-twin siblings are not genetically identical (well, that and symmetric variation on the mother's side).

The mechanism is, your somatic cells each have two "copies" of each of your chromosomes, one inherited from each parent. Each sperm cell, on the other hand, only gets one "copy" of each chromosome (either the one from your mom or your dad). So there are something like 2^23 different possible sperm configurations, which means that any two sperm are all but certain to have different information.

Or something like that!
posted by grobstein at 2:41 PM on July 6, 2012

No, your sperm don't all contain the same information.

You have 23 pairs of chromosomes - one of each you got from your mom, and the other of each you got from your dad. When sperm are made, they get one from each pair, but not the same ones (except that boys always get your 23-y and girls always get your 23-x).

(It gets even more complicated than this, because chromosomes aren't perfectly preserved as we 'use' them and pass them along and such. Sometimes your pairs can swap genes, or experience mutations, or they're not copied perfectly, etc. etc.)
posted by muddgirl at 2:41 PM on July 6, 2012

Each one has a random half of your DNA. So the contents of one might be completely identical to another, but it's much more likely that they will be different. Likewise, one might be entirely different to another with no overlap of data at all, but it's more likely that they will share some.

Though the lines of delineation are by chromosome, not by bit.
posted by -harlequin- at 2:41 PM on July 6, 2012

The "mutation" is a byproduct of sexual reproduction. Each child receives half of his/her DNA from each parent. Each parent contributes half of his/her DNA to each child-- which half that is, as Jehan mentioned, is random (roughly speaking; genes that are located near each other tend to "move" together). And then there's the issue of crossover... Oh, and actual mutation..
posted by supercres at 2:42 PM on July 6, 2012

Also, recombination occurs. This is why your haploid sperm result in kids that can't be grouped into only two sets.
posted by Tandem Affinity at 2:42 PM on July 6, 2012

Meiosis means that your sperm has half of your DNA, all mixed up differently in each sperm.
posted by randomnity at 2:42 PM on July 6, 2012

It's not mutation, your sons would be different because each sperm cell has different bits of your genetic information in them. For example (MUCH simplified), if your hair is Xx, half your sperm will have the big X and half will have the little. Then, if your eyes are Bb, 1/4 of your sperm will have XB, 1/4 Xb, 1/4 xb, 1/4 xB. Then, if your height is HH, you'll have XBH, XbH, xBH, XBh, xbH, XBh, Xbh, xbh... you get the gist. Imagine all the possible combinations. Staggering.
posted by arcticwoman at 2:44 PM on July 6, 2012 [1 favorite]

Response by poster: I obviously need to take some good biology and genetics classes. Thank you all for answering my dumb question.
posted by shipbreaker at 2:48 PM on July 6, 2012 [2 favorites]

except that boys always get your 23-y and girls always get your 23-x

More like, the sperm that get your 23-y lead to boys, and the sperm that get your 23-x lead to girls. If you've ever heard that "the male determines the sex of the baby," this is what they meant.
posted by ubiquity at 3:11 PM on July 6, 2012 [3 favorites]

It's a bit outdated now, but The Selfish Gene is a good starting place. I can't remember if it assumes basic knowledge of biology or not; I think Dawkins goes over the basics.
posted by supercres at 3:13 PM on July 6, 2012

I think all of this has been said but I'll try to sum up:

It's a semi-random half of the DNA. You only get one member of each chromosome pair, and which pair you get is random for each chromosome according to the Law of Independent Assortment. For humans, who have 23 pairs of chromosomes, this gives 223 or 8,388,608 possible combinations. On top of that you have recombination or crossing-over, where chromosome pairs will line up next to each other and swap bits back and forth. This isn't totally random because the bits they swap are ends, and while the length of that end can vary it's still more likely that a gene out at the end of the chromosome (near the telomere) will get swapped than one in the middle (near the centromere). This allows for a truly gigantic number of possible variations in the information carried by your gametes (sperm). I have no idea what this number is or if it's even known.

On top of that, you've always got random mutation. This happens at a pretty low rate per gene per division, but there are enough divisions happening and enough genes involved that it does happen, of course. This actually isn't totally random either as different segments of DNA have different mutation rates. (For instance, a gene that if modified will cause the cell to die probably will get passed down more or less intact from cell generation to cell generation, whereas a bunch of random junk in an intron or intergenic region that codes for nothing is more likely to get passed down. It's far, far more complicated than that but you get the idea.)

So there are several factors in play that cause your sperm to carry slightly different information from each other. Cool, right? If you have followup questions I don't mind trying to answer them.
posted by Scientist at 3:32 PM on July 6, 2012

Many people here seem to confused. Due to recombination and crossover, the chromosomes in each sperm are also different from each other. The one copy of a "chromosome 3" in a particular sperm is a combination of different bits of your two chromosome 3's, and different than either of them.

In terms of song titles, that sperm's version of Abbey Road might have a song called: "Octopus' Mustard"... Some from side A and some from side B.
posted by gregglind at 4:15 PM on July 6, 2012 [4 favorites]

Response by poster: But "Mean Mister Mustard" was titled as "Golden Slumbers (Medley)" !!
posted by shipbreaker at 4:21 PM on July 6, 2012

I don't think people are confused - recombination and crossover are pretty advanced topics. I asked my biologist husband how often crossover happens between any pair of chromosomes and he said "I don't know" (given, he's not a reproductive biologist). From his physiology book, it looks like the answer is "pretty often."
posted by muddgirl at 9:20 PM on July 6, 2012

the male determines the sex of the baby

...which leads to techniques like sperm sorting that can be used for sex selection. (Not currently FDA approved, however.)
posted by Rhomboid at 10:07 PM on July 6, 2012

« Older Please help me stop flipping out about my...   |   Abuse, anger; how far should I go to support my... Newer »
This thread is closed to new comments.