What does it take to have a son and daughter? Three fortune tellers said that if I marry my current boyfriend, I will have a son. Only one fortune teller said it was difficult.

It is a mystery to have boys and girls, but this mystery is not determined by fate, but by both men and women. Generally speaking, in the absence of artificial selection, the birth sex ratio is 1: 1. Fetal sex is determined by sex chromosome, YX stands for male and XX stands for female. There are 23 pairs of chromosomes in human body, 22 pairs are autosomes, and 1 pair is sex chromosomes.

chromosome

Why do some people want boys to have girls and some people need girls to have girls?

23 pairs of chromosomes

It is a boy. What's going on here? Since ancient times, there have been various speculations about this, but there is no scientific basis.

It was not until the early 20th century that scientists discovered chromosomes in human cells that the mystery of sex was revealed. It turns out that the birth of a boy and a girl is determined by a pair of sex chromosomes in a fertilized egg.

There are 23 pairs of chromosomes carrying genetic material in human somatic cells, of which 22 pairs are autosomes, all the genes contained in the 23 pairs are genetic information, and 1 pair is a sex chromosome, which determines the sex of the fetus. The types of trait genes contained in autosomes are the same for men and women, and there is no gender difference. Sex chromosomes are different. The male 1 sex chromosome consists of X chromosome and Y chromosome (the male genome becomes 22+XY), while the female 1 sex chromosome is X chromosome (the female genome becomes 22+XX). Half of the 23 pairs of chromosomes come from the father and the other half from the mother.

Human germ cells reproduce through meiosis, that is, 1 cell is divided into two, two cells are divided into four, and so on. In the process of immature germ cells developing into mature germ cells, the chromosomes in the cells undergo two divisions, and the last one is meiosis, that is, mature sperm or egg cells contain only 23 chromosomes, which is half of the original, of which 22 are autosomes, and 1 is a sex chromosome. The male sex chromosome 1 is XY, so one kind of sperm with X sex chromosome is called X sperm, and the other kind with Y sex chromosome is called Y sperm. The female sex chromosome 1 is XX, so all the eggs after division and maturation contain 1 sex chromosome. Therefore, there are two kinds of male sperm, while there are only 1 kind of female eggs. So having boys and girls depends on the type of male sperm cells.

oosperm

seminal fluid

Sperm and egg combine to form fertilized eggs. In this way, 23 chromosomes in sperm and 23 chromosomes in egg match into 23 pairs of chromosomes. If X sperm and egg combine, a pair of sex chromosomes in the fertilized egg is XX, and the fetus develops into a woman; If the Y sperm is combined with the egg, a pair of sex chromosomes in the fertilized egg will be XY, and the fetus will develop into a male. It can be seen that the birth of boys and girls depends on whether the sex chromosome carried by the man's sperm is X or Y, and has nothing to do with the egg. The sex of a child is determined at the moment of fertilization, and the decisive factors are equally divided.