what factors determine the sex of an unborn child?

Question

I mean, is it carried in the genes of the man or woman? Is it something that happens at the time of conception? I've noticed often that some families have lots of boys or lots of girls.

Answer 1

I don’t know how much detail you want to go into but I am guessing that you want more than Y makes a male and X makes female.

There are three levels of sex determination and differentiation in mammals: chromosomal, gonadal and phenotypic. These three levels follow in sequence from fertilization, to embryogenesis, and to postnatal development. The default path is female development.

The first, or primary, sex determination step is chromosomal with rare exceptions. It is the presence of the X or Y chromosome delivered by a sperm that sets up the next stage. If an X chromosome is delivered by the sperm, then the primordial gonads develop into ovaries. The Y chromosome is tiny compared to the other chromosomes and it has few protein coding genes. It carries the gene for testis determining factor (SRY) along with genes needed later for sperm production. If the sperm delivers a Y-chromosome, testis form which then secrete hormones to initiate gonadal determination. Rare recombination events can cause an XX individual to develop as male (DAX1 or SOX9 duplication) or an XY genotype (SRY translocation) to develop as female.

Gonadal sex (testis vs. ovaries) is determined in the genital ridge by a series of signaling steps. The genital ridge develops into a bipotential gonad. Without the Y chromosome that brings the SRY gene, the bipotential gonad becomes an ovary. The ovaries produce granulosa and thecal cells that secrete estrogen. When SRY is expressed from the Y chromosome, it works with SOX9 to induce testis. The testis make Sertoli cells and Leydig cells that make AMH and testosterone.

Phenotypic sex (male vs. female body structure) all the way into puberty is determined by the hormones secreted by the developing testes or ovaries. Testis secrete anti-Müllerian ducts hormones (AMH) that causes Müllerian duct regression and testosterone that stimulates the formation of the male ductal system, scrotum, penis and inhibits the development of breast primordia. Ovaries produce estrogen that enables the development of the Müllerian ducts into the uterus, oviducts and vagina.

As for the observation that some families have more girls or boys...that is a combination of human nature and large numbers. If you have a sample size large enough (flip a coin a few million times) one will inevitably encounter long runs of heads or tails. People tend to notice these cases as unusual and ignore all the other families with less interesting sex distributions.

It is interesting to note that more boys are born than girls. But boys are more likely to die during infancy and childhood so that the ratio evens out by adult age.

Answer 2

The factor is the X factor that is carried by the man. A man carries both an X and a Y chromosome, making up the sex chromosomes. A woman carries two X chromosomes, therefore if the woman can only contribute an X and a man can contribute an X or a Y, there is the formula.

Studies have shown that sperm containing the X chromosome and the sperm containing the Y chromosome swim at different rates in different conditions, like slight differences in pH. Something within the physiology of the woman and the man together may lean in favor of one gender or another, but usually the sampling size is so small, like less than 10, that not much can be inferred statistically in any one family.

In actuality, the very complex interplay of all the factors within a woman (and the man) that determine which sperm gets to fertilize the egg is beyond what modern medicine understands completely. But they are working on it every day, so stay tuned..........

Answer 3

Go to a library and read up on the first 5 Q? This is a very large topic and there are theories and then there are some. How often does a girl ovulate and from what age does this start ? They have two ovaries and each ovulates alternately in about 28 1/4 days, it is tied to lunar cycle. They can start ovulating at any time but as a rule not before 13 years of age. When is a womans body ready to bear children without risk to herself and what is the ideal age to bear children, and at what age should a woman stop having children ? Any time after ovulation begins, or even befor but rear but after an OK from a gynaecologist, because the other parts of the birthing mechanism may be under developed. After 25 years it should be safe. In USA doctor do take more steps to assure safe normal delivery if a woman is older then 30 years of age or younger then 22 years of age or is very small for her age. They do certain test and even do more sonograms. The chances of trouble pregnancy increases with the age after 30 years or there after, most literature recommend not having a child if they are over 36 years and it is their first child, without complete investigation by a gynaecologist. Ther are cases of woman giving natural birth at age 72 years but these are extreemly rear cases.

Answer 4

Sex is determined by the chromosome contributed in the fathers sperm. A mother contributes the X chromosome in her egg and if the father's sperm also carries an X chromosome than the baby will be a girl. If, however, the father's sperm carries the Y chromosome than the baby will be a boy.
Because of this sex is determined at conception but is traits don't appear until later in the preganancy.

Answer 5

Well, when sperm and egg meet during fertilization, they contain an important sex chromosome. Eggs always contain X chromosomes (named for their shape). Sperm, on the other hand can have either an X or a Y (also, shape). An XX combination produces a girl; an XY combination produces a boy. Males should, probability wise, have a 50/50 chance of producing either. It may in fact, just be chance that the families you speak of have lots of boys or lots of girls. I for one, however, believe there may be other unknown factors involved. At the very base of it though, the coupling of those chromosomes is the ultimate determinant of sex.

Answer 6

X and Y chromosomes are responsible for the sex or the child. Women carry release XX chromosomes while men release XY.
At the time of conception, if an X fuses with an X then it will be a girl. If an X fuses with a Y then the child will be a boy.

Answer 7

The sex of an unborn child is determined at the moment of conception. all female eggs are female and it's the male sperm that determines the sex.

Answer 8

Hi Emmie, it's determined by the number of X and Y chromosones in the sperm, so it's the man who determines the sex of the baby. It's determined at the time of conception, depending on which sperm fertilises the egg.

Which makes Henry VIII completely wrong!!

Answer 9

Well it can be both the male has the male or female sperm, but it is how long it takes to get to the egg which determines the sex. because males swim faster, but die sooner and females swim slower but live longer. So its all about timing and how soon you are ovulating. For example if you are trying right on ovulation, you have more chances of a boy. But if it is a few days to a week before ovulation, there is more chances of a girl. But some woman have trouble getting pregnant at certain times which leads to more chances of having the same sex multiple times.

Answer 10

The man's DNA splits into to 2 sperms. The man has an X and a Y chromosome. One sperm gets an X and the other gets the Y. Women have XX, therefore when her DNA splits each egg has an X chromosome. Then when the sperm fertilizes the egg, either a XX (female) or XY (male) is created.