Questions about the 50/50 ratio in hatching

[myfivegirls]

I've searched all over BYC, and can't seem to find an answer to a few questions about hatching.

Last year, I hatched out two batches of chicks under broody hens.
1st batch - set 6 eggs; 3 hatched - two roos & 1 pullet; eggs were from 2 Red Star hens & 1 Easter Egger hen

2nd batch - set 9 eggs - 7 hatched - 5 roos & 2 pullets; eggs were from the following with the resulting gender:
1 Wyandotte = roo
2 EE (not the same hen) = roos
2 Black Star - only have one hen = both roosters
2 Partridge Rock - only have one hen = both pullets!

So, obviously, I did not get a 50/50 ratio, and I've read many others have experienced this too. My "theory" is that I got more roos than pullets, because I only hatched out 1 or two eggs from each hen.

1. My first question is - What's the best way to get a 50/50 ratio when hatching?

2. If I want to hatch a total of 42 eggs - and get an average of 18-20 eggs a day, would it be better to ...
A. Hatch two or three days worth of eggs - obviously selecting the clean & normal shaped eggs;
B. Or hatch 6 days worth of eggs from only a few hens - try to select the identical eggs or those that are from the same hens. Therefore, you'd end up with 4-6 eggs from each hen, thereby increasing your chances of getting a better ratio;

3. Does the 50/50 ratio apply to each individual hen - as in one day's eggs will be a roo and the next day's a pullet? Or not?
A. For example, I have certain hens that I can tell their eggs apart from the others. If I were to hatch 6 days worth of eggs from that particular hen, would it be more likely to get a 50/50 ratio from those eggs?
B. What if I selected 2 eggs from 21 individual hens for the total 42 eggs to hatch? Would it be more likely for the ratio to become "unbalanced"?

If anyone has experiemented with this, I'd like to know!

Thanks.

 

[tdgill]

your theory makes sense to me

 

[Fred's Hens]

Back in statistics class in university, the professor used to say, "flip a coin 10 times". then, "flip a coin 100 times". In other words, 50/50 is what happens over a long period of time, on average. When our "sample" is just this particular rooster and these few hens, perhaps, it can be skewed. Hatch out 1000 chicks from 10 roosters and 100 hens? Probably be much closer to 50/50.

There is also some evidence, not much, but some, that incubation temperatures can skew the hatch rates too. Wish I could remember if hotter versus cooler produced what? I just cannot remember. LOL

 

[ChickensRDinos]

As far as I understand it, each egg individually has a 50/50 chance of being a certain gender.

This does not mean with a small sample size that you will get a 50/50 ratio. It is the same as flipping a coin. If you flip a coin only 4 times you might get 2 heads and 2 tails but you might get 4 heads. Each individual flip has a 50/50 shot just like each and every egg has its own 50/50 shot at beng a certain gender. What happened to the egg that was laid before it or after it does not effect that particular egg's 50/50 chance. (If 5 chicks have all hatched roosters and one egg is cracking, that unknown egg still has a 50/50 shot of being a rooster)

Statistically and mathematically speaking if you flip enough coins or hatch enough eggs each with their own 50/50 individual shot then the overall ratio will be close to 50/50. The more eggs the closer you will get to that ratio. (lots like 1000s)

So, if you were to look back at your hatch rate over a lifetime of breeding your overal ratio will likely be very close to 50/50 however this may not be evident with each individual hatch containing a small number of eggs.

Here is a good explanation on 50/50 statistics:

http://www.basic-mathematics.com/coin-toss-probability.html

 

[chickentooth]

In my expirience, the Hen makes the difference, some hens lay more female eggs and some lay more males. You just have to find the hen that lays more females. I like what your trying to do with your varibles and taking advantage of them but unless you know who is laying the mostly females and who is laying mostly males it will be hard to find the proper angle to work from.

50/50 shouldn't be that hard, with the most variables applied you should get close. So get as many as you can from as many different times and as many different hens that you can and that should be as close to random as possible which will yield closely to what is natural. 50/50

From there take notes on which hen layed what if you can and next time around pick eggs only from the hen who layed mostely females. That can get your numbers into the 60/40 range but beyond that its a crap shoot.

 

[ChickensRDinos]

deleted because the information I posted was incorrect. Please see below for a great explanation of ZZ:ZW chicken genetics.

 

[Fred's Hens]

Luck wise this might happen but biologically it is not possible as a rooster's sperm contains the genetic material that determines if an egg becomes a male or a female.

Each bird contributes one gene. XX = girl. XY = boy. A hen ALWAYS contributes that first X (as being genetically XX that is all she has to offer). The sperm will then either contribute an X or a Y (as genetically he is XY - this is where you get the 50/50 individual chance for each egg).

The hen biologically has no influence in the gender of her offspring.

Is that right? Are birds the same as mammals? I remember reading something about ZZ. Have to check that out.

 

[hallerlake]

Quote: They're not called X and Y. I can't remember what they're called either, but they function the same way as X and Y.

 

[1muttsfan]

Instead of XY, birds have a ZW chromosome system where the ovum determines the sex of the offspring - males are ZZ, while females are ZW (the W chromosome plays almost no part in physiology).

My statistics prof used to say that if you torture numbers long enough they will tell you anything you want to hear.

 

[chickentooth]

Luck wise this might happen but biologically it is not possible as a rooster's sperm contains the genetic material that determines if an egg becomes a male or a female.

Each bird contributes one gene. XX = girl. XY = boy. A hen ALWAYS contributes that first X (as being genetically XX that is all she has to offer). The sperm will then either contribute an X or a Y (as genetically he is XY - this is where you get the 50/50 individual chance for each egg).

The hen biologically has no influence in the gender of her offspring.

I don't agree with the above in mamals yes, in chickens no.
In chickens gender is determined not by X and Y chromosones. But rather by ZZ:ZW chromosone system. That of which is highly affected by the estrogen. The chicken embryo resembles lower vertebrates in that estrogens play a central role in gonadal sex differentiation. Not to say she can choose but she does infact influence her offspring. In case your wondering ZZ is the boy and ZW the girl.