Choosy Eggs May Pick Sperm for Their Genes, Defying Mendel’s Law

https://www.quantamagazine.org/choosy-eggs-may-pick-sperm-for-their-genes-defying-mendels-law-20171115/

by sprucely • 9 years ago

157 55 9 years ago

cwkoss• 9 years ago

Reminds me of the CS problem: write a program which prints out its own source code.

But way more impressive. How can a cell with a single strand of DNA 'decide' which copy of a gene is a mutation? Or do eggs just bias for sperm with more genetic differences?

jblow• 9 years ago

crc32

vikiomega9• 9 years ago

These decisions interface via binding sites[1] which can be thought of as having "bias".

[1] https://en.wikipedia.org/wiki/Binding_site

sjg0072• 9 years ago

If I understand correctly, they see associations of alleles in the zygotes that suggest the gametes have not paired randomly.

Basically it could be that the egg and the sperm have different proteins expressed on their cellular surfaces which go together like a lock and key and may also function as attractors ( chemical sensing or something).. all of this would originate from genes in the gametes.

chiefalchemist6• 9 years ago

Does this (read: could this) help explain why some couples have problems conceiving? Perhaps, at least in some cases, the egg is saying, "no way buddy."

thiagocsf• 9 years ago

I haven’t looked it up but I’d say there’s anectodal evidence of couples that conceived with different partners after having trouble conceiving between them.

novalis78• 9 years ago

Just met an airbnb host with the exact same story. Tried for years then broke up - both had kids right away with their new partners

Alex3917• 9 years ago

Perhaps, at least in some cases, the egg is saying, "no way buddy."

Assuming this is true, it would be happening in less than 1% of cases (given the prevalence of male-factor infertility and the prevalence of its known causes). So if such an ability exists, it doesn't seem to be getting used very often. Which, given the evolutionary complexity that would be required to evolve such a system, seems surprising. So my guess is that either that's not a thing, or else it exists only as a failure state of some other mechanism rather than as something that has evolved to directly confer some sort of reproductive advantage.

gjjrfcbugxbhf5• 9 years ago

I thought that partner incompatibility was extremely common?

golemotron• 9 years ago

The biggest issue in conception is the age of the mother [1]. As couples don't attempt pregnancy until later (often their mid 30s) this effect is masked as partner incompatibility.

[1] https://en.wikipedia.org/wiki/Age_and_female_fertility

klmr2• 9 years ago

Unlikely. As a selective mechanism its effect would be very subtle, and there are other, well-known, much stronger mechanisms that prevent conception. Age of the mother was mentioned. More generally, it’s defects in the oocyte’s ability to perform chromosome segregation or to nest in the uterine lining.

rllin• 9 years ago

I feel like this is a misunderstanding how strict Mendelian genetics is.

Most evolutionary theorists think more like physicists and do realize every trait is selectable.

gewa• 9 years ago

This... Mendel's law is only applicable to a really small hand full of traits.

dekhn• 9 years ago

Try saying that around a geneticist :( most i know consider mendelian genetics to apply to everything and nearly all traits/phylogenies are considered monogenic.

mannykannot• 9 years ago

This is a problem I have with this sort of journalism. In the big picture, the prevalence of the effect is low, and so we do not have to throw away all of reproductive and evolutionary biology as a consequence, but that is exactly what creationists will claim.

biomcgary• 9 years ago

The current evidence is inconclusive, but many obvious alternatives have been ruled out.

pishpash• 9 years ago

Furthermore, if true, it shouldn't be overly surprising, since gametes are another stage in the life of an organism with great selection pressure. Why assume it behaves randomly?

virmundi• 9 years ago

No known sense organs to pick another environmental benefit. Classic biology assumes such a means to respond by selecting in this case.

gowld• 9 years ago

Did they rule out the possibility that the mutant gene they put in the male mice caused the sperm to be bad at sperming?

psloth• 9 years ago

"Perhaps, Nadeau reasoned, the problem lay in the sperm, not the egg. He therefore bred male mice with and without the mutation to healthy mutation-free females and found no differences in the males’ fertility"

graeme• 9 years ago

I thought the standard view was that eggs did some selecting. At least, that’s what I gathered by reading about IVF and birth defects.

I can’t find a specific reference offhand though.

avdempsey• 9 years ago

Cool to seen this on HN; my wife did the illustration for this article!

caio19822• 9 years ago

She did a great job!

m3kw92• 9 years ago

It would make evolutionary sense to have the ability to select better sperm.

gweinberg• 9 years ago

It could if the egg could somehow know which ones were better. But how could it know that?

andai3• 9 years ago

The same way women do!

m3kw92• 9 years ago

Probably some sort of gene expression

sjg0072• 9 years ago

I thought there was evidence that the female immune system also "selects" against some sperm as well.

mozumder• 9 years ago

This probably answers a question I have about genetics - that there just isn't enough variety if reproduction was random.

Genetic differences that have no bearing on survivability, like skin patterns or colors or whatever, should be widespread through every species, but they're not.

andai3• 9 years ago

That's really interesting to think about. Somewhat related, I asked a geneticist once why there was so much diversity in humans vs pigeons which all looked the same to me.

He said, "We're tuned to notice differences between people, not pigeons. Perhaps we all look the same to them!"

Perhaps there is precisely this sort of random variation in the differences we don't notice, because by being oblivious to them they are not sexually selected for or against?

rsynnott• 9 years ago

If anything, humans have abnormally _small_ genetic diversity; most species have more. We went through a population trap at some point in the past, and nearly went extinct; we probably lost most of our diversity then.

azeotropic• 9 years ago

Skin patterns and colors do have impacts on survivability! Some species use camouflage to avoid predation, others use bright coloration to attract mates.

There's also a flaw in your premise -- reproduction is not random, it's subject to selection at a number of levels. Most selective forces act to reduce genetic diversity, both at the selected gene, and at nearby genes.

amelius• 9 years ago

Not a biologist, but wouldn't an alternative hypothesis be that the DDX1 gene somehow affects the sperm cell's physical abilities, e.g. motility?

skate22• 9 years ago

So... we are the chosen ones?

rscar• 9 years ago

Don't be surprised if Todd Akin comes out of the woodwork to say he was right.

i.e. Mr. "It seems to be, first of all, from what I understand from doctors, it’s really rare. If it’s a legitimate rape, the female body has ways to try to shut the whole thing down."

phaitour• 9 years ago

this is interestingly in line with chinese traditional medicines perspective on reproduction. their theory is that it’s heavily based on the receptability of the egg and therefore it’s largely the mother who’s largely in control of things like gender selection. things like eating more acidic or basic foods affect the environment for the sperm to swim in and even the month of the mother’s life has an effect on what the egg would choose.

Choosy Eggs May Pick Sperm for Their Genes, Defying Mendel’s Law

Related Stories