# Do baby boys run in families? Uh, I mean... come inside, I'll explain

Marie Osmond is the only girl in a family of nine children. The Osmonds being devout Mormons they’ve procreated a bit and the results are somewhat interesting:

Brother Alan has 8 sons, no daughters.

Brother Donnie has 5 sons, no daughters.

Brother Jay has 3 sons, no daughters.

The other brothers have daughters, but with the exception of Jimmy (2 sons, 2 daughters) they all have more sons than daughters. (Virl, one of the two oldest non-musical brothers [they’re both deaf] has six sons and two daughters.)

I use the Osmonds because they’re famous, but my grandfather’s family was similar. He was one of 10 brothers; 6 sons were born before the first daughter and 9 sons before the second daughter. Of the 52 children born to the 10 brothers, 40 (or just under 80%) were male, though the children born to the five sisters (and to Marie Osmond) were a more equal ratio.

On the flip side I worked with a lady who had one brother and twelve sisters, but generally I’ve known more families with a disproportate number of sons to daughters. (My brother-in-law had no contact with his father from the time he was an infant until he was an adult, but when they reunited he found out that his father had 7 sons by 4 women, no daughters; actress Hayley Mills’s first husband was a dirty old man who had 9 sons and no daughters by a variety of wives and girlfriends.)

I’m completely aware that the gender of a child is determined 100% by the father, but is there a gene that makes men far more likely to have sons than to have daughters? Or vice versa? I was wondering if the Osmonds and my grandfather’s brothers and the others named are coincidence (if you flip a coin sometimes it will happen to come up heads 8 times in a row) or have their been studies about whether or not some families are predominantly male? (In the case of my grandfather, he had 2 sons and 2 daughters and some of his other brothers had equally mixed families, but he also had brothers who had large families that were all boys and brothers whose families had a 4:1 boy:girl ratio and the like.)

FWIU, genes don’t have anything to do with it. Having a boy or girl is 50/50. Having 3 boys is a 1:8 chance but having the 3rd one is a 1:2 chance. If anything it is the environmental factor that determines sex. To me that would put the ball in both parent’s court. I believe I read that male sperm swim faster under certain temperatures. If the mother’s biological environment is more receptive to the male sperm then it is her fault. The same with the father. IANAD and could be wrong on all points, but this is what i heard from several people including my wife’s OBGYN about the 50/50. I don’t remember where I heard about the environment factor but it made sense to me considering the other.

Well, absolutely in some families there is a predominance of one or the other. It is certainly not common, and would in fact be far more common to have for instance 10 boys in a row by chance (that’s 1:1024 10-children families). Most are not completely exclusive, although there are certainly rare genetic mechanisms that can account for it. Many inherited genetic diseases skew the gender ratio, for instance Incontinentia Pigmenti or Rett Syndrome which are both X-linked dominant and lethal in male fetuses.

For genetic syndromes to cause this, though, one has to imagine a scenario where the male germline is affected completely (or predominantly) while the rest of the father is unaffected – this can happen with genetic mosaicism or a new mutation early in the development of the germline. Both of these are pretty rare. More complicated genetic mechanisms could account for other mechanisms of this happening (trans lethality would be a nice example). I just don’t know of these happening in humans, although we do certainly exploit it in the genetic model that I trained on, the fruit fly. Female flies store sperm, so in order to ensure correct mating for crosses, you have to collect virgins (you can tell by the way they walk and their plaid dresses). We have certain crosses called “virginmakers” that produce only female flies, where harmless alleles in a mother and father combine to kill all male progeny during development.

There are many other reasons why gender ratio can be skewed. There are some studies which show different gender representations based on when during a woman’s cycle fertilization occurs. So we know there are factors such as motility that are different between X-containing and Y-containing sperm. It is not unreasonable to think that things like this and cervical mucus and such, as well as habits for instance when a couple is having sex during the month, could affect gender bias.

Doesn’t that depend on the assumption that the guy has one X and one Y chromosome? I’m hoping someone will be along to fix my knowledge of biology if it’s faulty, but as I understand it in sperm formation, the complete set of chromosomes is divided into two sperm cells. If a guy had XYY for his 23rd “pair” then it could easily divide so that one sperm carried XY and the other carried Y. (The alternatives would be dividing into X / YY or XYY / nothing.)

Y plus a woman’s X makes XY, a boy.
XY plus a woman’s X makes XXY, a boy.
YY plus a woman’s X makes XYY, a boy.
X plus a woman’s X makes XX, a girl.

It might be reasonable to assume that the two XY/YY alternatives wouldn’t be viable, except that we know of men who are XYY-- meaning they had to get both Y chromosomes from their fathers. It is reasonable to assume that they are less likely to be viable than a single-X or single-Y sperm cell. However, since any sperm cell carrying more than one 23rd chromosome in this instance is going to produce a boy, then adding in any viable sperm at all to the 50/50 X or Y mix is going to bias the chances toward a boy.

Having more than one of the two chromosome is an anomaly, and pretty rare. I’m not 100% sure, but I think its usually an individual sperm’s problem rather than for all the sperm produced by that man.

If no else knows, I’ll check back and research tomorrow.

Nitpick : Actually, it’s more like 51/49. Slightly more boys than girls are born, for some reason.

I was the oldest child of 5. After me was a run of four girls in a row. The first child got XY, but went girl anyway. Made me wonder if something was up with that–but Mr. Occam told me he’d bet on random luck of the draw.

My high school anatomy teacher said that certain egg temperatures are more receptive to certain sperm, that if the egg is too hot it will kill off either X or Y sperm (forget which). So if a woman has eggs that are always too hot (or cold) it could attract or reject certain types of sperm. I don’t have any cite other than that barely remembered knowledge, but it seems to make sense.

Hijack tangent: Do “supermales” (XYY) have a different ratio of X and Y sperm than regular males? I know in an XY it is close to 50/50.

One reason I have heard is that the Y sperm swim faster then the X ones, perhaps less mass due to the shorter Y chromosoemm. So it gets to the egg first

Another theory I have heard, sort of counter to the above is that the X is a slower swimmer but has more endurence. so if the egg comes in later, most Y’s have already dies off.

Either way, or some other, if there really is a difference it would seem like the woman would be the deciding factor, as she provided the enviorment the the sperm must exist in.

They make four kinds of sperm: X, Y, XY, and YY. They should occur in equal proportions and produce children that are XX, XY, XXY, and XYY, respectively. I don’t recall off the top of my head if the XY or YY sperm are less viable at all.

Hang on…I tell a lie. I think XY and Y should be more common than the others, since out of three ways an XYY cell could split during meiosis, two of them will give you XY/Y and one will give you X/YY.

Nope, that would mean that you are depending on a nondisjunction event at every meiosis. Nondisjunction is relatively rare; most sperm produced are X or Y containing.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=search&term=xyy+sperm+distribution+phenotype

I’ve heard this too, and have a daughter to “prove” it. (OK, not really prove it, but we did try to time our intercourse to this effect, and it worked for us.)

What it means in reality is that having intercourse 4-5 days before ovulation and then not again until after ovulation (after ovulation it’s recreational, not procreational) is more likely to get you a girl. The fast, weaker males die off before ovulation occurs or swim off past the fallopian tube into the abdomen, and the slower heartier females survive to be there when the egg descends. Having sex again close to ovulation gives those later added fast swimming boys a shot at it. If you want to better your boy chances, you hold off until intercourse the day before you ovulate, so there’s no old, slow, hearty females already up there.

So it may be, and this is total WAG, that couples with lots of boys have sex more often then couples with lots of girls. The addition of more sperm closer to ovulation gives the males an advantage, though not as great as abstinence until ovulation. But if their pattern is frequent sex around her ovulation time, boys are more likely.

So it may be the behavior pattern of the parents influencing the gender of their children. I won’t hazzard a guess as to whether sexual behavior patterns are similar in families, but it’s possible libido itself is genetic, or that some men have inherited more powerful sexual response to female fertility signs and respond accordingly.

Not particularly relevant, but maybe interesting. Our first born was a girl, the first female in five generations of my direct line. Our next two were boys, so we stopped.

This is fairly common in animal breeding.

In horses, some stallions are well known for sireing more colts or more fillies. Most stallions are roughly even in the sex of offspring, but some are 15%-20% leaning toward one gender. And that tendency is often very desirable for a breeder.

(Forfamous examples in Morgan stallions, see: General Gates 61% female, UVM Flash 54% female, or Upwey Ben Don 56% male)

And this is when crossed with lots of different mares, so it seems likely that this is something genetic in that particular stallion.

I don’t see why the same possibility wouldn’t apply to humans.

I read a fascinating book some time ago, Adam’s Curse by Bryan Sykes. It expalined or purported to explain why, genetically, the Y chromosome has created a world where men overwhelmingly own the wealth and power, commit the crimes, and fight the wars. But more relevant to this discussion he explains there is a genetic “war” between the Y chromosome and the mitochondrial DNA (passed) only by the mother. The Y chromosome strives to produce boys and the mitochondrial DNA stives to produce girls.

“Strives” of course puts purpose behind these actions. Rather Y chromosomes that somehow beat X chromosomes to fertilize eggs will produce more offspring and be selected for since the next generation obviously needs males. (The Y chromosome “reasons” let the other guy waste his time making girls babies.) Converesly anything the mitochondrial DNA does to make female offspring more likely will also be selected for as only through the females is it passed along. I no longer recall any of the details. Nor do I know how well accepted his theory is.

Well, I don’t know about the wealth and power, but men tend to get the risky jobs because we’re more expendable. If half your men are killed in a bloody war, but all the women survive, the population will grow back just as quickly as if nobody were killed at all (assuming that the society accepts polygamy, at least). If, on the other hand, you lose half your women, you’ve got problems. So men tend to fight the wars, hunt the dangerous animals, etc. Because of this, there’s benefit to men being more aggressive, by and large, than women, and because men are more agressive, they tend to commit more crimes. This is regardless of the Y chromosone: Among birds, the opposite chromosone pattern occurs (males have a matching pair, while females have a mismatched pair), and male birds are more agressive than female birds.

Why would the matching or nonmatching of chromosomes have anything to do with aggression?

The OP made me wonder; what are the sexes of Marie Osmond’s children?

Chronos , that explains things!

Is there anything that would make a male produce more one than the other? Diet, drugs, or perhaps some sort of medical condition or predisposition?