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Is it true some couples can only have either all male or all female DC?

112 replies

maybemumm · 09/11/2023 18:51

My friend is pregnant and her DP has two daughters from another relationship. She said the baby would be a girl because her DP only makes girls, and it’s just confirmed to be a girl.

Is it true that some couples (men, in particular, as I know it’s men who influence it) can only biologically make either female or male offspring?

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thecatinthetwat · 10/11/2023 00:48

Study on divers found no significant difference in sex ratios of offspring (sample of 10000 babies).

MrsJellybee · 10/11/2023 06:34

My extended family is prone to girls with only one boy born each generation. The 'boy' seems to be following down a particular line also.

SandwichDog · 10/11/2023 09:11

DisforDarkChocolate · 09/11/2023 23:06

Well I have brothers and sisters, as do my children. So its obviously not true, unless you think nearly all women are unfaithful?

The question was whether, "some couples (men, in particular, as I know it’s men who influence it) can only biologically make either female or male offspring?"

The fact that your parents and you and your partner, and plenty of other people clearly can have both sexes does not answer the question.

Eggandcresssandwich · 10/11/2023 09:27

The answer is no! Some couples cannot ‘only’ biologically make either female or male offspring.
However some couples may have a predisposition towards making either female or male offspring.

BertieBotts · 10/11/2023 09:49

It's extremely unlikely.

The idea that a man could produce "only one type of sperm" is absolutely false, it's totally impossible and anyone thinking this needs to go back and redo year 9 biology.

The vast majority of men have XY chromosomes. When sperm is created the chromosomes are split in half. There will always be equal numbers of X sperm and Y sperm created. It's not possible for a man to create no Y sperm - he would need to be XX chromosome, in which case he'd be female. It's not possible for him to create no X sperm - he'd be YY chromosome, which doesn't exist, a zygote formed with this combination would be rejected as too much genetic material would be missing.

There are some genetic mutations which result in a man being XXY or XYY - these are rare, and their sperm will still be produced with both X and Y chromosomes (I believe in this case, the "extra" chromosome is passed on in the sperm and may be inherited, but these conditions are usually caused by a random mutation). XXY is also associated with fertility problems. XYY is less so as I understand, but it wouldn't produce twice the amount of sperm with Y chromosome. It would produce a normal amount of X chromosome and then either all the Y chromosomes are also YY or a proportion of the Y chromosomes are YY and some are Y. (If I understood this correctly!)

The specific chromosomes that are present in a sperm cell do not affect its ability to reach the egg, that isn't possible. However, it is possible for a man to carry a genetic defect on either the X or Y chromosome which causes fertilised eggs to be rejected by the body or causes miscarriage. So it is possible in rare cases for a man to produce only VIABLE sperm of one sex. But he will still produce sperm with the opposite chromosome in equal numbers, it's just that they won't result in viable embryos.

And, again, this is rare.

OTOH, the chances of producing all one sex just by chance are very high, and if you already have several the same sex then it's always a 49/51 chance - which is extremely high. Therefore people come to incorrect conclusions because they have a "hunch" (oh it must be he can only make boys/girls) and then it's proven right on essentially a coin flip, so they cement this idea when actually the highest likelihood is it's just chance.

Think about it - people rarely claim this before their first baby and then it's totally right. They usually claim it when they already have two (or more) of the same sex, and then they have a 50/50 chance to get another of the same sex.

Chances of having 2 children the same sex: 50% (2/4 possible combinations = 1 in 2)
Chances of 3 children the same sex: 25% (2/8 possible combinations = 1 in 4)
Chance of 4 children the same sex: 12.5 % (2/16 poss combo = 1 in 8)

Etc. The chances of having one of the chromosome disorders are roughly 1 in 500. It's only after having 10 children the same sex in a row that the chromosome disorder is more likely than random chance.

For typical numbers of children in a family (2 up to about 4 or even 5) the likelihood of it being random chance is much much more likely than genetic disorder.

SirVixofVixHall · 10/11/2023 09:53

Male sperm are not as tough as female sperm, so men will be much more likely to only have girls, if they do anything that has an impact on sperm. This can be cycling, working in a hot environment, even wearing tight clothes. Lots of things can affect sperm.
Some men according to my Doc, do produce more sperm more of one sex and are therefore much more likely to have girls than boys, or vice versa.

BertieBotts · 10/11/2023 09:56

Deadringer · 09/11/2023 19:19

Scientifically no, it should be 50/50, but anecdotally, lots of couples seem to have only boys or only girls despite having lots of dc and the odds being 50/50 every time.

These things aren't mutually exclusive, because a lot of people have multiple children. It's just that you notice it more when it happens. Also, there is a behavioural component. If you want both a boy and a girl, and you get them within the first 2/3 pregnancies, most people stop having children and so don't end up with a larger family. Whereas, if you've had two or three children of the same sex, there is (sometimes) a desire there to keep going "in case we get a girl/boy" - obviously most people say publically that they would be happy with either, and should not continue unless they are happy with either. But then if it does not happen, which is quite a high chance as they already have several the same sex, the family decide that they do not want more than 4/5 children and stop trying anyway. If they had continued, it's likely that eventually they would have had a child of the opposite sex.

You can do your own probability experiment by recording concurrent coin flips. You will find that it's quite frequent to get fairly long stretches of heads or tails, even though it seems like it should be evently split. Randomness just doesn't work that way, it works out even over a much longer period. We look at the small period and conclude that it must not be random, but we're wrong.

Dontcallmescarface · 10/11/2023 10:21

My sister has 4 DC by 2 different men. Her elder 2 (with her 1st husband), are different sexes and her younger 2 (2nd husband), are twins, but also different sexes, so going by that single piece of "evidence" I'm saying it's not true.

ETA 2nd husband had 3 boys with his 1st wife but both a boy and girl with my sister.

Stressfordays · 10/11/2023 10:23

My DGM on my Mums side had 7 dc. BBBBGGB

DGM on Dads side BG

My mum BBG

I Had BBG my db had G

I find it fascinating I had exactly the same as my Mum (same age gaps too) my dc Dad came from BBB and I believe a still born girl was in the mix.

greengreengrass25 · 10/11/2023 17:32

My dh's dgf was one of 5 boys but there were 2 girls at the end so his dm had to have lots of boys first

Dh df is one of 3 brothers who all have 2 sons each

However all this generation has had a mix of sexes

GETTINGLIKEMYMOTHER · 10/11/2023 17:45

I once read a piece by some fertility guru, who said that it was noticeable that in couples where any fertility problems were down to the man, if they did eventually go on to have a baby, it was considerably more likely to be a boy.

At around the same time (Rugby World Cup of 2003 IIRC) at least 2 or 3 of our winning team (we beat the Aussies 👍) had just fathered girls.

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