The nuclei of human cells contain 23 pairs of chromosomes for a total of 46. There are 22 pairs of autosomes and one and 2 sex chromosomes.
Chromosomes are long, stringy aggregates of genes that carry heredity information and are located within the nucleus of our cells, whether you are a male or female depends on the presence or absence of certain chromosomes, also they determine physical characteristics , everything from skin, hair, eye color and also hereditary disease conditions.
Sex chromosomes are particular chromosomes that are involved in determining the sex of an organism. The sex chromosomes are the X chromosome and the Y chromosome.
Eggs and sperm, as reproductive cells, each contain only one of the two sex chromosomes, what sex a baby will be is decided when the egg and sperm unite.
Eggs carry only an X and sperm carry either an X or a Y, if an egg is fertilized by a sperm carrying an X chromosome an XX or female embryo will result, while fertilization of the egg by a Y-bearing sperm will produce an XY or male embryo.
Summarizing: The sex of an individual is determined by which paternal sex chromosome (X or Y) is inherited at fertilization.
X+X means the cell will develop into a girl.
X+Y means that it will develop into a boy.
X+Y means that it will develop into a boy.
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