Source
r/genetics•
RegularGuest

[ask genetics] sexual selection doesn't give your offspring half your genes in practice right? Does this help explain alturism?

Question

A good chunk of our genome is highly conserved. Areas that encode key protein production are basically the same in me as they are in you. Let's call the percentage of the genome that is highly conserved C%. Then if we mate the true variation that we pass on is (1 - C%) / 2 which is less than 50% and conversely the amount that we share with our offspring is 1 - (1 - C%) / 2 or 1/2 + C% which is greater than 0.5

Wikipedia has the following question regarding sexual selection:

Why sexual reproduction exists, if in many organisms it has a 50% cost (fitness disadvantage) in relation to asexual reproduction?[7]

Given what I wrote above this question is not quite correct, right?

On to alturism,

It the conserved bit of our genome means that if you pick 2 random strangers then they share C% of their genome. That means they are related by more than just the standard greatest ancestor calculation, and therefore it can make sense for you (from a selfish gene POV) to sacrifice your self for a bunch of strangers (providing C% * number of people > 1).

I think this is especially true if you as a species are highly stressed and close to extinction.

Posted Aug 8, 2018, 8:33 PM UTC

08
RomanticonPhD in genetics/biology•

Why are you subtracting the highly conserved portions of the genome?

You pass on roughly half your genetic material to your child. Yes, if you and your partner both have the same version (allele) of a gene, it's pretty obvious what the child will get. If you have gene version A, and your mate has gene version A, your child will definitely get gene version A...

...but it's still being passed on from one of the parents. If you could fluorescently color the paternal genes green and the maternal genes blue, you'd see that gene A came from one of the parents.

Even if you ignore conserved regions, it means that of the total variable regions in the genome, half of those came from your father and half from your mother. Still 50% from each parent.

"alturism" - do you mean altruism?

Yes, the idea of sacrificing yourself to preserve your genetic lineage is well documented and makes logical sense. It's worth giving up your life to save:

  • 2 brothers, at 50% similarity each;
  • 4 grandchildren, at 25% similarity each; or
  • 8 cousins, at 12.5% similarity each.
11
High_Point_Genetics•

Don’t forget about the 1-4% of coding genes that are parent-of-origin specific (imprinted).

2
RomanticonPhD in genetics/biology•

Sure, but those are only a couple hundred genes out of the 20,000 in a human.

2
smockerer•

Yes, one theory is that altruistic behaviors are evolutionarily favored because of shared ancestry even if the recipient is not a first degree relative. This is the kinship selection mentioned in Richard Dawkins's "Selfish Gene"

Your math at the beginning is not quite right. We do in fact pass on precisely 50% of our genetic material, (even though large portions of the genome are the same in both parents). I understand your point that the "50% cost" might be partially offset by shared ancestry in parents that encourages altruistic behaviors toward the offspring. However, I encourage you to think about it like this:

Of the unique portions of a parent's genome (i.e. portions that are not shared with the partner), 50% (on average) will be passed to the offspring.

Note that in this scenario, the "50%" is actually an average, and depends on ancestral population structure, relatedness to the partner, as well as the meiotic crossover pattern for each gamete. It can in theory be as little as 0% and as much as 100%

3
Koloradio•

Genes that don't vary in the population aren't visible to selection, only the variable genes matter

1
High_Point_Genetics•

Some variants only affect phenotype in the presence of other rare variants at different loci, so the genes that “matter” to selective forces are difficult to quantify.

1
Koloradio•

If there's no variation, then there would be no rare variants, yes?

1
zoofboof11•

I find that a lot of people seem to get caught up on the conserved regions of DNA when it comes to inheritance. The very large percentage of DNA that is conserved is made up mostly of introns which do not code for proteins or like the OP stated, proteins that are necessary for the normal functioning of the organism. The non-conserved regions of DNA are what you should be concerned with in terms of inheritance. With regards to your question about the offspring getting half of the parental genes, that is a bit more complicated. The offspring gets EXACTLY 50% of each parents chromosomes. Where this gets a little more complicated is that mitochondrial genes are only inherited from the mother so that would give each offspring slightly more genes from the mother than the father. Also with regards to the sex-genes (X and Y), the X-chromosome contains 850 known genes where the Y chromosome contains around 50 known genes. With regards to males, they would receive the 50 Y-chromosome genes from the father and the 850 X-chromosome genes from the mother. With regards to females, the will receive the fathers only copy of 850 genes on the X-chromosome and one of two copies of the X-Chromosome from the mother. The Y-chromosome is what determines gender mainly with regards to the SRY-gene which is a key contributor to male development and the lack of a Y-chromosome causes female development due to the lack of the genes which cause male development. The reason sexual reproduction exists and why every organism doesn't go through asexual reproduction is because sexual reproduction creates genetic variation which is key to evolution. Organisms which are more capable of evolution are generally better at adapting to their environment and thus their "fitness" (Darwinian Fitness) is higher than those that are less capable.

With regards to the "altruism" part of the question you might want to take that to a psychology/sociology page because that has nothing to do with genetics.

1