hen determines gender of chicks

I didn't want to hijack CynthiaM's post on candling update.  A question arose from something Uno said about putting out the focus to get a lot of hens, very effective in getting the opposite!  She has more roosters than hens hatch.  I wondered if maybe it was a genetic propensity amongst a strain within a breed(s) to have the upper hand on gender and if so, would one want to cull and seek other stock if you were wishing to raise more pullets than cockerels.  Something flickered through the back rooms in my mind about which parent governs the sex of the offspring.  I wondered if there was such a scientific fact.  A quick look and I found this, thought it was interesting although I don't profess to understand the genetic language entirely  -  still in genetics preschool and thinking I need to get a book called "Genetics For Dummies" (if it exists):

we need to understand that in avian species sex is not determined by the male, but by the female. The hen has the chromosome which lacks information and by which presence determines sex. Where male humans are XY and female humans XX, roosters are ZZ and hens Z0 (sometimes written ZW). So the male is needed to fertilize the egg, but it is the hen that determines the sex. Also, some hens tend to produce a larger percentage of offspring of one sex, just as in mammals some males tend to produce either more daughters or more sons. Add this all together and you can see that if you have a hen that tends to produce largely daughters and lays round eggs, or produces largely sons and happens to lay pointed eggs, she will "prove" that egg shape determines sex.
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Incidentally, think this article is from a magazine called Backyard Poultry Magazine.  Looks good.  Need to post on Uno's post about what material and publications we all like to read.  
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Yes, the female determines the sex of the chick, in all birds.
Don't be fooled by the "round egg -pointy egg" argument - if there were a consistent trend, the poultry industry would have taken advantage of it ages ago. There is no consistent trend linking egg shape to sex of offspring.

my mother still believes :-). Now I can give her the back story for the "why" on how people came to believe that shape = gender thing. I understand how it came to be but realize it is variable, you would have to know your chickens very well to be able to identify trends and each one might lay the opposite shape some days and some days not, one hen might have a tendancy to lay pointed ones that are roosters and another the opposite. I had a talk with her recently about it and she said she found the trait to be true (pointy ones more likely to be roosters) - I went "pfft!" but I guess she was very observant of her particular flock and the rule worked within her flock. Hope that made sense. I don't do scientific stuff too well but working on it. pedantic language.

What I found interesting, that I realize now is probably not news to everyone here but was to me (last to the party on most occasions   ) is about how it is the hen who may be more likely to lay a higher percentage of eggs fertilised either female or male and if you wanted more roosters than pullets or vice versa then you could work to effect a flock who performed more to your preference.

Your first link disputes egg shape and size determining sex.

Many people think that egg shape can somehow determine the sex of the chick that will hatch. According to this school of thought, pointed or elongated eggs will hatch cockerels and round eggs pullets. I have experimented with this over the years (and there have been scientific studies as well) and the results reveal this method to be nearly useless. Pullets have been hatched from pointed eggs, males from round. If this method had worked, then the poultry industry would have been using this instead of paying for professionals to vent sex day-old chicks.

I believe the hen does not mentally choose the sex of her offspring. Each egg has a 50-50 chance depending on the genetics it randomly receives.

Ah...and here we go off the rails.

You may indeed have a hen who creates more female eggs than male eggs.

However...you still have to get those eggs to hatch at 100% rate in order to effectively determine this. ANd it has to happen more than once. That hen will have to hatch more hens than roos over and over and over to make a secure guess that she lays more hens than roos.

If a hen has 10 eggs, 4 roos, 6 hens, but 6 of those eggs die before hatching, you have NO WAY OF KNOWING the sex of the dead embryo. Therefore, from the chicks that do hatch, you have NO RELIABLE WAY of telling if she has more female eggs or male eggs. You do not know the sex ratio you started with, therefore the sex ratio you end with tells you nothing about whether or not she lays more hens than roos.

I ALWAYS end up with more roosters than hens. Last year had one batch of 9 eggs hatch, every one of them was a rooster! This made me wonder if I didn't have a lethal gene or something killing off all the female embryos. I inquired and the answer was, maybe.

I have never had a 50/50 blend of the sexes. I hatch very small numbers and without fail hatch more roosters. Are roos a stronger embryo? Are female eggs more prone to incubator temp fluctuations or humidity problems? I have no way of knowing if the dead eggs are female or male and without that crucial piece of information, can have no way of knowing if any hen lays more females than males. I also have no way of knowing if I have a bad gene in there killing off all the girls.

While we may know the hen determines sex, I think that to determine whether a hen lays girl eggs or boy eggs, everything has to go perfectly, over many, many hatches, before a 'trend' can be identified.

Ha ha on you, Uno. I always get more hens. Perhaps it is my dedication to a moist hatch! You need to rethink your dry ways.

However, I am probably wrong on that. I have a 95%-100% hatch rate of fertile eggs.

Or, I have discovered that low/no humidity results in mostly males hatching. Who knew! I'm practically a genius!