Genetics: Boy/Girl?

Ok, in my non-majors bio class we just finished our total of two days talking about genetics, etc. According to what we learned, gender of the baby is determined by the man (this I already knew, of course), and each time you concieve there is a brand new 50/50 chance for a boy or a girl. So, the question is, why do certain genders seem more common is some families? For instance:
[ul][li]My maternal grandfather had one sister and two brothers.[/li][li]My mother had three brothers, no sisters, and all male (first) cousins (at least on her father’s side).[/li][li]I have four brothers, no sisters, and all male (first) cousins (all are on my mother’s side, my father was an only child).[/ul][/li]Is this simply coincidence, or is there some biological factor that is causing all of the men in my family to have sons?


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Maybe they have a low count of X spermies.


Small sample size and a tendency to personalize statistics.

I have heard of many different factors that influence gender:

Social standing of the mother - Dominant position in the social structure gives a 2% increase in prob of a male.

Orgasm - gives a 2% increase in prob of a male.

Stress increases chance of a girl
However, boys are more likely during war.

Multiple “sessions” increase chance of a boy.

Viscosity & acidity of the mucus are supposed to change the probabilities.

Position is supposed to change the probabilities.

None of these have a major impact on the probabilities; many of them could be overlapping, e.g. stress changes the uterine environment.

It’s not really as simple as your class made it out to be, eh?

Dr Fidelus, I was just using my family as an example, I’ve heard many more cases of this. Many people I know have families that seem to produce more of one gender than the other. Why are you getting snippy?

Me? Snippy? Perish forfend.

I was just pointing out that one family, and only three generations of that family, is a small enough sample size to show a great bias from the mean. Rather like getting a run of twelve heads in a row while flipping a coin. Random fluctuation, and an increase in sample size will flatten it out.

Ok, that makes more sense and sounds less snippish. :slight_smile:

“Social standing” meaning? If I’m more popular than my husband? If my family is wealthier?

Some clarity for my feeble mind, please… I find this a rather interesting subject. (I’m also looking for any number of straws to grasp at to ensure that my next child is a girl… :))

Veni, Vidi, Visa … I came, I saw, I bought.

I know a lady who has 12 kids(she’s 37)and most are girls!I suppose it’s all in the genetics,but 50/50 is pretty random.

I have heard (but cannot point to) fairly recent studies that showed that the pH of the woman’s reproductive system has something to do with whether X or Y sperms tend to survive better. Alas, that’s all I can say off the top of my head.

That said, I come from a family of 3 boys; my wife comes from a family of 3 girls. If this played a major role, you’d expect us to have girls. We don’t – we have 2 boys. < shrug >

Girls are a rare commodity in our family.

In my generation there are 26 kids, 22 of them boys.Of the four girls, two are adopted. In the generation we’ve spawned, there are 24 kids, and only four girls.( with one more on the way.)

There is one theory by some Doctor ( Shipler?) who’s name escapes me that if you want a boy, wait until the day you ovulate to have sex. The logic is( If I understand this) that boy spermies are slow movers and don’t ask for directions ( well, duh) and don’t last as long in the canal. If you want a girl, then start a couple of days before you ovulate because girl spermies hang out and go shopping or whatever waiting for the big egg to come along.

My husband says its all in the hips and how a guy moves them. If its the usual minute man rush job, you’ll have a boy. ( Ahem, not that he ever does something like that…cough) if you want a girl, you wiggle side to side.

Everyone wants to save the world, but no one wants to help Mom with the dishes.-P.J. O’Rourke

I remember reading that fighter pilots have a lot of girls, because the female biased sperm tend to survive hi-g stresses better. And yes, I said female biased, I believe it is possible to have an XX male, because there are a number of genes that determine gender, and not all of them are on the X and Y chromosomes. I might be wrong about this, but I have talked with a few genetisists about it, considering it an interesting thing to talk about.

>>Being Chaotic Evil means never having to say your sorry…unless the other guy is bigger than you.<<

—The dragon observes

In the article I read this in, the effect showed up in both humans & monkeys. Since social status is a bit more apparent in monkeys: in monkey social units, the females have a “pecking” order, where there will be one female who is dominant over all of the others, then one below her, etc. with the dominant females more likely to have boys & the females lower on the pecking order more likely to have females. Note that status equates to a better share of resources(more & better food, males more likely to get to mate) The researchers postulated that since males got their status from their mother, whereas females got their status from their mate, this allowed both dominant & non-dominant females to maximize their offsprings status.

In human terms, this probably equates to the more subtle indicators of money, power and the status you have in your circle of friends.
If you want to have a girl, you could put yourself under a lot of stress, or make sure you don’t orgasm during sex. Personally, I’d go for the stress. :wink:

If the dominant females have boys, but their social standing comes from their mates, doesn’t this essentially mean that the dominant males are having boys?


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I’m pretty sure more boys are conceived than girls. Statistically, boys start dying off by the time of conception and continue to do so as the demographic ages and at the other end of the spectrum (70+) there are more women than men.

of course these statistics don’t explain y’all’s families. Must be some freak-of-nature thing.

Life is short. Make fun of it.

As for the women outliving men statistic, I think this is because a woman wants the remote to herself and the toilet paper hanging her way for the last few years of her life on earth.

Toilet paper greed causing an increased lifespan? Surely U jest! :wink:

But seriously, folks – I’ve also heard that menstrual cycles tend to synchronize with those of the dominant woman in a group of women living together. Maybe the gender preference for the offspring of dominant women is triggered in her mate by all those dominance pheromones he’s inhaling…

The truth, as always, is more complicated than that.

From the “More Than You Wanted To Know” Files:
The menstrual cycles of any group of women living together or otherwise closely associated will synchronise if not otherwise stabilised (by the pill, frinstance).

Wife and I used this book for a boy. It apparently worked. But of course…small sampling of population…miniscule in fact!