Comment by robocat
3 days ago
It is just a filter for certain cellular traits. It doesn't filter for many other important traits. A good flagellum doesn't indicate good kidneys. A sperm's existence indicates the father made faithful copies of cells, however the new sperm DNA could be terrible at making faithful copies (ability not proven until after fertilisation).
It also depends on how much of the sperm cell comes from the fathers genes, and how much is generated from the new DNA. I didn't find a clear answer to this but the following indicates that the new sperm cell is at least somewhat generated by the sperm DNA:
Because nucleotide recombinations can occur during meiosis I, the genetic code of chromosomes of gametes can differ from that of somatic parent cells (ie., progeny cells might express cell-surface antigens that are recognized by the host [the father] as foreign and thus be eliminated by humoral or cellular immune mechanisms). Occluding junctions that interconnect adjacent Sertoli cells shield secondary spermatocytes, spermatids, and spermatozoa from autoimmune recognition.
I wonder if there are any organisms where the sperm envelope is made by the dad, and the DNA letter is contained inside?
And I'm completely ignoring the mitochondria (Dad's copy are not passed on so should be mostly irrelevant to sperm selection pressures). I'm pretty ignorant of this whole topic - high school biology only.
I suppose it’s a question of perspective.
The best sperm will likely result in the next generation of sperm also being good.
We look at the human as the organism, the sperm as the gamete - but perhaps our logic is anthropocentric - perhaps the sperm is the organism, and we are just the ridiculously elaborate reproductive mechanism.
The current best guess is that animals evolved from https://en.wikipedia.org/wiki/Choanoflagellate They look quite similar to sperm.
I remember something like they may have sexual reproduction and even form blastulas, but the Wiki article is not very clear, so I may be misremembering.
> we are just the ridiculously elaborate reproductive mechanism
That is the point behind Dawkins' The Selfish Gene.
The book well argues that genes are what reproduce, and that everything else is just complications to reproduce genes.
Humbling book - not light reading but I love it and I read it again and again because of the unobvious insights into systems.
We are (for genes, though, not sperm)
100% of sperm dna comes from father.
but each chromosome could be "grandfathers" or "grandmothers", and usually those chromosomes have one or two crossover events, so, the chromosome goes FFFFFFFFMM for example. (where F = grandfather and M = grandmother)
I assumed F = Frances and M = Michael, my paternal grandparent's names, so thanks for the clarification.
Does that mean gendering a baby is more determined by factors on the father's side?
Whats interesting to me is that along with the autosomes (chr1-22) the sperm contributes either an X or Y sex chromosome. The X chromosome is large and carries a lot of important genes. The Y chromosome on the other-hand is much smaller and carries very few functional genes (primarily just SRY).
So If you think about it girls get ~5% more genetic material from their father than boys.
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Yes. Sperm cells are haploid. If the sperm that fertilizes the egg has an X chromosome, the baby will be female. If it has a Y chromosome, the baby will be male.
There are rare exceptions for genetic disorders relating to sex development, but generally speaking the above is true.
I never explored this scientifically but I have this hunch that a man with more sisters than brothers will tend to have more daughters than sons
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